1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 /*
  22  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  23  * Copyright (c) 2012, Joyent, Inc. All rights reserved.
  24  * Copyright (c) 2011, 2014 by Delphix. All rights reserved.
  25  * Copyright (c) 2014 by Saso Kiselkov. All rights reserved.
  26  * Copyright 2014 Nexenta Systems, Inc.  All rights reserved.
  27  */
  28 
  29 /*
  30  * DVA-based Adjustable Replacement Cache
  31  *
  32  * While much of the theory of operation used here is
  33  * based on the self-tuning, low overhead replacement cache
  34  * presented by Megiddo and Modha at FAST 2003, there are some
  35  * significant differences:
  36  *
  37  * 1. The Megiddo and Modha model assumes any page is evictable.
  38  * Pages in its cache cannot be "locked" into memory.  This makes
  39  * the eviction algorithm simple: evict the last page in the list.
  40  * This also make the performance characteristics easy to reason
  41  * about.  Our cache is not so simple.  At any given moment, some
  42  * subset of the blocks in the cache are un-evictable because we
  43  * have handed out a reference to them.  Blocks are only evictable
  44  * when there are no external references active.  This makes
  45  * eviction far more problematic:  we choose to evict the evictable
  46  * blocks that are the "lowest" in the list.
  47  *
  48  * There are times when it is not possible to evict the requested
  49  * space.  In these circumstances we are unable to adjust the cache
  50  * size.  To prevent the cache growing unbounded at these times we
  51  * implement a "cache throttle" that slows the flow of new data
  52  * into the cache until we can make space available.
  53  *
  54  * 2. The Megiddo and Modha model assumes a fixed cache size.
  55  * Pages are evicted when the cache is full and there is a cache
  56  * miss.  Our model has a variable sized cache.  It grows with
  57  * high use, but also tries to react to memory pressure from the
  58  * operating system: decreasing its size when system memory is
  59  * tight.
  60  *
  61  * 3. The Megiddo and Modha model assumes a fixed page size. All
  62  * elements of the cache are therefore exactly the same size.  So
  63  * when adjusting the cache size following a cache miss, its simply
  64  * a matter of choosing a single page to evict.  In our model, we
  65  * have variable sized cache blocks (rangeing from 512 bytes to
  66  * 128K bytes).  We therefore choose a set of blocks to evict to make
  67  * space for a cache miss that approximates as closely as possible
  68  * the space used by the new block.
  69  *
  70  * See also:  "ARC: A Self-Tuning, Low Overhead Replacement Cache"
  71  * by N. Megiddo & D. Modha, FAST 2003
  72  */
  73 
  74 /*
  75  * The locking model:
  76  *
  77  * A new reference to a cache buffer can be obtained in two
  78  * ways: 1) via a hash table lookup using the DVA as a key,
  79  * or 2) via one of the ARC lists.  The arc_read() interface
  80  * uses method 1, while the internal arc algorithms for
  81  * adjusting the cache use method 2.  We therefore provide two
  82  * types of locks: 1) the hash table lock array, and 2) the
  83  * arc list locks.
  84  *
  85  * Buffers do not have their own mutexes, rather they rely on the
  86  * hash table mutexes for the bulk of their protection (i.e. most
  87  * fields in the arc_buf_hdr_t are protected by these mutexes).
  88  *
  89  * buf_hash_find() returns the appropriate mutex (held) when it
  90  * locates the requested buffer in the hash table.  It returns
  91  * NULL for the mutex if the buffer was not in the table.
  92  *
  93  * buf_hash_remove() expects the appropriate hash mutex to be
  94  * already held before it is invoked.
  95  *
  96  * Each arc state also has a mutex which is used to protect the
  97  * buffer list associated with the state.  When attempting to
  98  * obtain a hash table lock while holding an arc list lock you
  99  * must use: mutex_tryenter() to avoid deadlock.  Also note that
 100  * the active state mutex must be held before the ghost state mutex.
 101  *
 102  * Arc buffers may have an associated eviction callback function.
 103  * This function will be invoked prior to removing the buffer (e.g.
 104  * in arc_do_user_evicts()).  Note however that the data associated
 105  * with the buffer may be evicted prior to the callback.  The callback
 106  * must be made with *no locks held* (to prevent deadlock).  Additionally,
 107  * the users of callbacks must ensure that their private data is
 108  * protected from simultaneous callbacks from arc_clear_callback()
 109  * and arc_do_user_evicts().
 110  *
 111  * Note that the majority of the performance stats are manipulated
 112  * with atomic operations.
 113  *
 114  * The L2ARC uses the l2arc_buflist_mtx global mutex for the following:
 115  *
 116  *      - L2ARC buflist creation
 117  *      - L2ARC buflist eviction
 118  *      - L2ARC write completion, which walks L2ARC buflists
 119  *      - ARC header destruction, as it removes from L2ARC buflists
 120  *      - ARC header release, as it removes from L2ARC buflists
 121  */
 122 
 123 #include <sys/spa.h>
 124 #include <sys/zio.h>
 125 #include <sys/zio_compress.h>
 126 #include <sys/zfs_context.h>
 127 #include <sys/arc.h>
 128 #include <sys/refcount.h>
 129 #include <sys/vdev.h>
 130 #include <sys/vdev_impl.h>
 131 #include <sys/dsl_pool.h>
 132 #ifdef _KERNEL
 133 #include <sys/vmsystm.h>
 134 #include <vm/anon.h>
 135 #include <sys/fs/swapnode.h>
 136 #include <sys/dnlc.h>
 137 #endif
 138 #include <sys/callb.h>
 139 #include <sys/kstat.h>
 140 #include <zfs_fletcher.h>
 141 
 142 #ifndef _KERNEL
 143 /* set with ZFS_DEBUG=watch, to enable watchpoints on frozen buffers */
 144 boolean_t arc_watch = B_FALSE;
 145 int arc_procfd;
 146 #endif
 147 
 148 static kmutex_t         arc_reclaim_thr_lock;
 149 static kcondvar_t       arc_reclaim_thr_cv;     /* used to signal reclaim thr */
 150 static uint8_t          arc_thread_exit;
 151 
 152 #define ARC_REDUCE_DNLC_PERCENT 3
 153 uint_t arc_reduce_dnlc_percent = ARC_REDUCE_DNLC_PERCENT;
 154 
 155 typedef enum arc_reclaim_strategy {
 156         ARC_RECLAIM_AGGR,               /* Aggressive reclaim strategy */
 157         ARC_RECLAIM_CONS                /* Conservative reclaim strategy */
 158 } arc_reclaim_strategy_t;
 159 
 160 /*
 161  * The number of iterations through arc_evict_*() before we
 162  * drop & reacquire the lock.
 163  */
 164 int arc_evict_iterations = 100;
 165 
 166 /* number of seconds before growing cache again */
 167 static int              arc_grow_retry = 60;
 168 
 169 /* shift of arc_c for calculating both min and max arc_p */
 170 static int              arc_p_min_shift = 4;
 171 
 172 /* log2(fraction of arc to reclaim) */
 173 static int              arc_shrink_shift = 5;
 174 
 175 /*
 176  * minimum lifespan of a prefetch block in clock ticks
 177  * (initialized in arc_init())
 178  */
 179 static int              arc_min_prefetch_lifespan;
 180 
 181 /*
 182  * If this percent of memory is free, don't throttle.
 183  */
 184 int arc_lotsfree_percent = 10;
 185 
 186 static int arc_dead;
 187 
 188 /*
 189  * The arc has filled available memory and has now warmed up.
 190  */
 191 static boolean_t arc_warm;
 192 
 193 /*
 194  * These tunables are for performance analysis.
 195  */
 196 uint64_t zfs_arc_max;
 197 uint64_t zfs_arc_min;
 198 uint64_t zfs_arc_meta_limit = 0;
 199 int zfs_arc_grow_retry = 0;
 200 int zfs_arc_shrink_shift = 0;
 201 int zfs_arc_p_min_shift = 0;
 202 int zfs_disable_dup_eviction = 0;
 203 int zfs_arc_average_blocksize = 8 * 1024; /* 8KB */
 204 
 205 /*
 206  * Note that buffers can be in one of 6 states:
 207  *      ARC_anon        - anonymous (discussed below)
 208  *      ARC_mru         - recently used, currently cached
 209  *      ARC_mru_ghost   - recentely used, no longer in cache
 210  *      ARC_mfu         - frequently used, currently cached
 211  *      ARC_mfu_ghost   - frequently used, no longer in cache
 212  *      ARC_l2c_only    - exists in L2ARC but not other states
 213  * When there are no active references to the buffer, they are
 214  * are linked onto a list in one of these arc states.  These are
 215  * the only buffers that can be evicted or deleted.  Within each
 216  * state there are multiple lists, one for meta-data and one for
 217  * non-meta-data.  Meta-data (indirect blocks, blocks of dnodes,
 218  * etc.) is tracked separately so that it can be managed more
 219  * explicitly: favored over data, limited explicitly.
 220  *
 221  * Anonymous buffers are buffers that are not associated with
 222  * a DVA.  These are buffers that hold dirty block copies
 223  * before they are written to stable storage.  By definition,
 224  * they are "ref'd" and are considered part of arc_mru
 225  * that cannot be freed.  Generally, they will aquire a DVA
 226  * as they are written and migrate onto the arc_mru list.
 227  *
 228  * The ARC_l2c_only state is for buffers that are in the second
 229  * level ARC but no longer in any of the ARC_m* lists.  The second
 230  * level ARC itself may also contain buffers that are in any of
 231  * the ARC_m* states - meaning that a buffer can exist in two
 232  * places.  The reason for the ARC_l2c_only state is to keep the
 233  * buffer header in the hash table, so that reads that hit the
 234  * second level ARC benefit from these fast lookups.
 235  */
 236 
 237 typedef struct arc_state {
 238         list_t  arcs_list[ARC_BUFC_NUMTYPES];   /* list of evictable buffers */
 239         uint64_t arcs_lsize[ARC_BUFC_NUMTYPES]; /* amount of evictable data */
 240         uint64_t arcs_size;     /* total amount of data in this state */
 241         kmutex_t arcs_mtx;
 242 } arc_state_t;
 243 
 244 /* The 6 states: */
 245 static arc_state_t ARC_anon;
 246 static arc_state_t ARC_mru;
 247 static arc_state_t ARC_mru_ghost;
 248 static arc_state_t ARC_mfu;
 249 static arc_state_t ARC_mfu_ghost;
 250 static arc_state_t ARC_l2c_only;
 251 
 252 typedef struct arc_stats {
 253         kstat_named_t arcstat_hits;
 254         kstat_named_t arcstat_misses;
 255         kstat_named_t arcstat_demand_data_hits;
 256         kstat_named_t arcstat_demand_data_misses;
 257         kstat_named_t arcstat_demand_metadata_hits;
 258         kstat_named_t arcstat_demand_metadata_misses;
 259         kstat_named_t arcstat_prefetch_data_hits;
 260         kstat_named_t arcstat_prefetch_data_misses;
 261         kstat_named_t arcstat_prefetch_metadata_hits;
 262         kstat_named_t arcstat_prefetch_metadata_misses;
 263         kstat_named_t arcstat_mru_hits;
 264         kstat_named_t arcstat_mru_ghost_hits;
 265         kstat_named_t arcstat_mfu_hits;
 266         kstat_named_t arcstat_mfu_ghost_hits;
 267         kstat_named_t arcstat_deleted;
 268         kstat_named_t arcstat_recycle_miss;
 269         /*
 270          * Number of buffers that could not be evicted because the hash lock
 271          * was held by another thread.  The lock may not necessarily be held
 272          * by something using the same buffer, since hash locks are shared
 273          * by multiple buffers.
 274          */
 275         kstat_named_t arcstat_mutex_miss;
 276         /*
 277          * Number of buffers skipped because they have I/O in progress, are
 278          * indrect prefetch buffers that have not lived long enough, or are
 279          * not from the spa we're trying to evict from.
 280          */
 281         kstat_named_t arcstat_evict_skip;
 282         kstat_named_t arcstat_evict_l2_cached;
 283         kstat_named_t arcstat_evict_l2_eligible;
 284         kstat_named_t arcstat_evict_l2_ineligible;
 285         kstat_named_t arcstat_hash_elements;
 286         kstat_named_t arcstat_hash_elements_max;
 287         kstat_named_t arcstat_hash_collisions;
 288         kstat_named_t arcstat_hash_chains;
 289         kstat_named_t arcstat_hash_chain_max;
 290         kstat_named_t arcstat_p;
 291         kstat_named_t arcstat_c;
 292         kstat_named_t arcstat_c_min;
 293         kstat_named_t arcstat_c_max;
 294         kstat_named_t arcstat_size;
 295         kstat_named_t arcstat_hdr_size;
 296         kstat_named_t arcstat_data_size;
 297         kstat_named_t arcstat_other_size;
 298         kstat_named_t arcstat_l2_hits;
 299         kstat_named_t arcstat_l2_misses;
 300         kstat_named_t arcstat_l2_feeds;
 301         kstat_named_t arcstat_l2_rw_clash;
 302         kstat_named_t arcstat_l2_read_bytes;
 303         kstat_named_t arcstat_l2_write_bytes;
 304         kstat_named_t arcstat_l2_writes_sent;
 305         kstat_named_t arcstat_l2_writes_done;
 306         kstat_named_t arcstat_l2_writes_error;
 307         kstat_named_t arcstat_l2_writes_hdr_miss;
 308         kstat_named_t arcstat_l2_evict_lock_retry;
 309         kstat_named_t arcstat_l2_evict_reading;
 310         kstat_named_t arcstat_l2_free_on_write;
 311         kstat_named_t arcstat_l2_abort_lowmem;
 312         kstat_named_t arcstat_l2_cksum_bad;
 313         kstat_named_t arcstat_l2_io_error;
 314         kstat_named_t arcstat_l2_size;
 315         kstat_named_t arcstat_l2_asize;
 316         kstat_named_t arcstat_l2_hdr_size;
 317         kstat_named_t arcstat_l2_compress_successes;
 318         kstat_named_t arcstat_l2_compress_zeros;
 319         kstat_named_t arcstat_l2_compress_failures;
 320         kstat_named_t arcstat_memory_throttle_count;
 321         kstat_named_t arcstat_duplicate_buffers;
 322         kstat_named_t arcstat_duplicate_buffers_size;
 323         kstat_named_t arcstat_duplicate_reads;
 324         kstat_named_t arcstat_meta_used;
 325         kstat_named_t arcstat_meta_limit;
 326         kstat_named_t arcstat_meta_max;
 327 } arc_stats_t;
 328 
 329 static arc_stats_t arc_stats = {
 330         { "hits",                       KSTAT_DATA_UINT64 },
 331         { "misses",                     KSTAT_DATA_UINT64 },
 332         { "demand_data_hits",           KSTAT_DATA_UINT64 },
 333         { "demand_data_misses",         KSTAT_DATA_UINT64 },
 334         { "demand_metadata_hits",       KSTAT_DATA_UINT64 },
 335         { "demand_metadata_misses",     KSTAT_DATA_UINT64 },
 336         { "prefetch_data_hits",         KSTAT_DATA_UINT64 },
 337         { "prefetch_data_misses",       KSTAT_DATA_UINT64 },
 338         { "prefetch_metadata_hits",     KSTAT_DATA_UINT64 },
 339         { "prefetch_metadata_misses",   KSTAT_DATA_UINT64 },
 340         { "mru_hits",                   KSTAT_DATA_UINT64 },
 341         { "mru_ghost_hits",             KSTAT_DATA_UINT64 },
 342         { "mfu_hits",                   KSTAT_DATA_UINT64 },
 343         { "mfu_ghost_hits",             KSTAT_DATA_UINT64 },
 344         { "deleted",                    KSTAT_DATA_UINT64 },
 345         { "recycle_miss",               KSTAT_DATA_UINT64 },
 346         { "mutex_miss",                 KSTAT_DATA_UINT64 },
 347         { "evict_skip",                 KSTAT_DATA_UINT64 },
 348         { "evict_l2_cached",            KSTAT_DATA_UINT64 },
 349         { "evict_l2_eligible",          KSTAT_DATA_UINT64 },
 350         { "evict_l2_ineligible",        KSTAT_DATA_UINT64 },
 351         { "hash_elements",              KSTAT_DATA_UINT64 },
 352         { "hash_elements_max",          KSTAT_DATA_UINT64 },
 353         { "hash_collisions",            KSTAT_DATA_UINT64 },
 354         { "hash_chains",                KSTAT_DATA_UINT64 },
 355         { "hash_chain_max",             KSTAT_DATA_UINT64 },
 356         { "p",                          KSTAT_DATA_UINT64 },
 357         { "c",                          KSTAT_DATA_UINT64 },
 358         { "c_min",                      KSTAT_DATA_UINT64 },
 359         { "c_max",                      KSTAT_DATA_UINT64 },
 360         { "size",                       KSTAT_DATA_UINT64 },
 361         { "hdr_size",                   KSTAT_DATA_UINT64 },
 362         { "data_size",                  KSTAT_DATA_UINT64 },
 363         { "other_size",                 KSTAT_DATA_UINT64 },
 364         { "l2_hits",                    KSTAT_DATA_UINT64 },
 365         { "l2_misses",                  KSTAT_DATA_UINT64 },
 366         { "l2_feeds",                   KSTAT_DATA_UINT64 },
 367         { "l2_rw_clash",                KSTAT_DATA_UINT64 },
 368         { "l2_read_bytes",              KSTAT_DATA_UINT64 },
 369         { "l2_write_bytes",             KSTAT_DATA_UINT64 },
 370         { "l2_writes_sent",             KSTAT_DATA_UINT64 },
 371         { "l2_writes_done",             KSTAT_DATA_UINT64 },
 372         { "l2_writes_error",            KSTAT_DATA_UINT64 },
 373         { "l2_writes_hdr_miss",         KSTAT_DATA_UINT64 },
 374         { "l2_evict_lock_retry",        KSTAT_DATA_UINT64 },
 375         { "l2_evict_reading",           KSTAT_DATA_UINT64 },
 376         { "l2_free_on_write",           KSTAT_DATA_UINT64 },
 377         { "l2_abort_lowmem",            KSTAT_DATA_UINT64 },
 378         { "l2_cksum_bad",               KSTAT_DATA_UINT64 },
 379         { "l2_io_error",                KSTAT_DATA_UINT64 },
 380         { "l2_size",                    KSTAT_DATA_UINT64 },
 381         { "l2_asize",                   KSTAT_DATA_UINT64 },
 382         { "l2_hdr_size",                KSTAT_DATA_UINT64 },
 383         { "l2_compress_successes",      KSTAT_DATA_UINT64 },
 384         { "l2_compress_zeros",          KSTAT_DATA_UINT64 },
 385         { "l2_compress_failures",       KSTAT_DATA_UINT64 },
 386         { "memory_throttle_count",      KSTAT_DATA_UINT64 },
 387         { "duplicate_buffers",          KSTAT_DATA_UINT64 },
 388         { "duplicate_buffers_size",     KSTAT_DATA_UINT64 },
 389         { "duplicate_reads",            KSTAT_DATA_UINT64 },
 390         { "arc_meta_used",              KSTAT_DATA_UINT64 },
 391         { "arc_meta_limit",             KSTAT_DATA_UINT64 },
 392         { "arc_meta_max",               KSTAT_DATA_UINT64 }
 393 };
 394 
 395 #define ARCSTAT(stat)   (arc_stats.stat.value.ui64)
 396 
 397 #define ARCSTAT_INCR(stat, val) \
 398         atomic_add_64(&arc_stats.stat.value.ui64, (val))
 399 
 400 #define ARCSTAT_BUMP(stat)      ARCSTAT_INCR(stat, 1)
 401 #define ARCSTAT_BUMPDOWN(stat)  ARCSTAT_INCR(stat, -1)
 402 
 403 #define ARCSTAT_MAX(stat, val) {                                        \
 404         uint64_t m;                                                     \
 405         while ((val) > (m = arc_stats.stat.value.ui64) &&            \
 406             (m != atomic_cas_64(&arc_stats.stat.value.ui64, m, (val))))     \
 407                 continue;                                               \
 408 }
 409 
 410 #define ARCSTAT_MAXSTAT(stat) \
 411         ARCSTAT_MAX(stat##_max, arc_stats.stat.value.ui64)
 412 
 413 /*
 414  * We define a macro to allow ARC hits/misses to be easily broken down by
 415  * two separate conditions, giving a total of four different subtypes for
 416  * each of hits and misses (so eight statistics total).
 417  */
 418 #define ARCSTAT_CONDSTAT(cond1, stat1, notstat1, cond2, stat2, notstat2, stat) \
 419         if (cond1) {                                                    \
 420                 if (cond2) {                                            \
 421                         ARCSTAT_BUMP(arcstat_##stat1##_##stat2##_##stat); \
 422                 } else {                                                \
 423                         ARCSTAT_BUMP(arcstat_##stat1##_##notstat2##_##stat); \
 424                 }                                                       \
 425         } else {                                                        \
 426                 if (cond2) {                                            \
 427                         ARCSTAT_BUMP(arcstat_##notstat1##_##stat2##_##stat); \
 428                 } else {                                                \
 429                         ARCSTAT_BUMP(arcstat_##notstat1##_##notstat2##_##stat);\
 430                 }                                                       \
 431         }
 432 
 433 kstat_t                 *arc_ksp;
 434 static arc_state_t      *arc_anon;
 435 static arc_state_t      *arc_mru;
 436 static arc_state_t      *arc_mru_ghost;
 437 static arc_state_t      *arc_mfu;
 438 static arc_state_t      *arc_mfu_ghost;
 439 static arc_state_t      *arc_l2c_only;
 440 
 441 /*
 442  * There are several ARC variables that are critical to export as kstats --
 443  * but we don't want to have to grovel around in the kstat whenever we wish to
 444  * manipulate them.  For these variables, we therefore define them to be in
 445  * terms of the statistic variable.  This assures that we are not introducing
 446  * the possibility of inconsistency by having shadow copies of the variables,
 447  * while still allowing the code to be readable.
 448  */
 449 #define arc_size        ARCSTAT(arcstat_size)   /* actual total arc size */
 450 #define arc_p           ARCSTAT(arcstat_p)      /* target size of MRU */
 451 #define arc_c           ARCSTAT(arcstat_c)      /* target size of cache */
 452 #define arc_c_min       ARCSTAT(arcstat_c_min)  /* min target cache size */
 453 #define arc_c_max       ARCSTAT(arcstat_c_max)  /* max target cache size */
 454 #define arc_meta_limit  ARCSTAT(arcstat_meta_limit) /* max size for metadata */
 455 #define arc_meta_used   ARCSTAT(arcstat_meta_used) /* size of metadata */
 456 #define arc_meta_max    ARCSTAT(arcstat_meta_max) /* max size of metadata */
 457 
 458 #define L2ARC_IS_VALID_COMPRESS(_c_) \
 459         ((_c_) == ZIO_COMPRESS_LZ4 || (_c_) == ZIO_COMPRESS_EMPTY)
 460 
 461 static int              arc_no_grow;    /* Don't try to grow cache size */
 462 static uint64_t         arc_tempreserve;
 463 static uint64_t         arc_loaned_bytes;
 464 
 465 typedef struct l2arc_buf_hdr l2arc_buf_hdr_t;
 466 
 467 typedef struct arc_callback arc_callback_t;
 468 
 469 struct arc_callback {
 470         void                    *acb_private;
 471         arc_done_func_t         *acb_done;
 472         arc_buf_t               *acb_buf;
 473         zio_t                   *acb_zio_dummy;
 474         arc_callback_t          *acb_next;
 475 };
 476 
 477 typedef struct arc_write_callback arc_write_callback_t;
 478 
 479 struct arc_write_callback {
 480         void            *awcb_private;
 481         arc_done_func_t *awcb_ready;
 482         arc_done_func_t *awcb_physdone;
 483         arc_done_func_t *awcb_done;
 484         arc_buf_t       *awcb_buf;
 485 };
 486 
 487 struct arc_buf_hdr {
 488         /* protected by hash lock */
 489         dva_t                   b_dva;
 490         uint64_t                b_birth;
 491         uint64_t                b_cksum0;
 492 
 493         kmutex_t                b_freeze_lock;
 494         zio_cksum_t             *b_freeze_cksum;
 495         void                    *b_thawed;
 496 
 497         arc_buf_hdr_t           *b_hash_next;
 498         arc_buf_t               *b_buf;
 499         uint32_t                b_flags;
 500         uint32_t                b_datacnt;
 501 
 502         arc_callback_t          *b_acb;
 503         kcondvar_t              b_cv;
 504 
 505         /* immutable */
 506         arc_buf_contents_t      b_type;
 507         uint64_t                b_size;
 508         uint64_t                b_spa;
 509 
 510         /* protected by arc state mutex */
 511         arc_state_t             *b_state;
 512         list_node_t             b_arc_node;
 513 
 514         /* updated atomically */
 515         clock_t                 b_arc_access;
 516 
 517         /* self protecting */
 518         refcount_t              b_refcnt;
 519 
 520         l2arc_buf_hdr_t         *b_l2hdr;
 521         list_node_t             b_l2node;
 522 };
 523 
 524 static arc_buf_t *arc_eviction_list;
 525 static kmutex_t arc_eviction_mtx;
 526 static arc_buf_hdr_t arc_eviction_hdr;
 527 static void arc_get_data_buf(arc_buf_t *buf);
 528 static void arc_access(arc_buf_hdr_t *buf, kmutex_t *hash_lock);
 529 static int arc_evict_needed(arc_buf_contents_t type);
 530 static void arc_evict_ghost(arc_state_t *state, uint64_t spa, int64_t bytes);
 531 static void arc_buf_watch(arc_buf_t *buf);
 532 
 533 static boolean_t l2arc_write_eligible(uint64_t spa_guid, arc_buf_hdr_t *ab);
 534 
 535 #define GHOST_STATE(state)      \
 536         ((state) == arc_mru_ghost || (state) == arc_mfu_ghost ||        \
 537         (state) == arc_l2c_only)
 538 
 539 /*
 540  * Private ARC flags.  These flags are private ARC only flags that will show up
 541  * in b_flags in the arc_hdr_buf_t.  Some flags are publicly declared, and can
 542  * be passed in as arc_flags in things like arc_read.  However, these flags
 543  * should never be passed and should only be set by ARC code.  When adding new
 544  * public flags, make sure not to smash the private ones.
 545  */
 546 
 547 #define ARC_IN_HASH_TABLE       (1 << 9)  /* this buffer is hashed */
 548 #define ARC_IO_IN_PROGRESS      (1 << 10) /* I/O in progress for buf */
 549 #define ARC_IO_ERROR            (1 << 11) /* I/O failed for buf */
 550 #define ARC_FREED_IN_READ       (1 << 12) /* buf freed while in read */
 551 #define ARC_BUF_AVAILABLE       (1 << 13) /* block not in active use */
 552 #define ARC_INDIRECT            (1 << 14) /* this is an indirect block */
 553 #define ARC_FREE_IN_PROGRESS    (1 << 15) /* hdr about to be freed */
 554 #define ARC_L2_WRITING          (1 << 16) /* L2ARC write in progress */
 555 #define ARC_L2_EVICTED          (1 << 17) /* evicted during I/O */
 556 #define ARC_L2_WRITE_HEAD       (1 << 18) /* head of write list */
 557 
 558 #define HDR_IN_HASH_TABLE(hdr)  ((hdr)->b_flags & ARC_IN_HASH_TABLE)
 559 #define HDR_IO_IN_PROGRESS(hdr) ((hdr)->b_flags & ARC_IO_IN_PROGRESS)
 560 #define HDR_IO_ERROR(hdr)       ((hdr)->b_flags & ARC_IO_ERROR)
 561 #define HDR_PREFETCH(hdr)       ((hdr)->b_flags & ARC_PREFETCH)
 562 #define HDR_FREED_IN_READ(hdr)  ((hdr)->b_flags & ARC_FREED_IN_READ)
 563 #define HDR_BUF_AVAILABLE(hdr)  ((hdr)->b_flags & ARC_BUF_AVAILABLE)
 564 #define HDR_FREE_IN_PROGRESS(hdr)       ((hdr)->b_flags & ARC_FREE_IN_PROGRESS)
 565 #define HDR_L2CACHE(hdr)        ((hdr)->b_flags & ARC_L2CACHE)
 566 #define HDR_L2_READING(hdr)     ((hdr)->b_flags & ARC_IO_IN_PROGRESS &&  \
 567                                     (hdr)->b_l2hdr != NULL)
 568 #define HDR_L2_WRITING(hdr)     ((hdr)->b_flags & ARC_L2_WRITING)
 569 #define HDR_L2_EVICTED(hdr)     ((hdr)->b_flags & ARC_L2_EVICTED)
 570 #define HDR_L2_WRITE_HEAD(hdr)  ((hdr)->b_flags & ARC_L2_WRITE_HEAD)
 571 
 572 /*
 573  * Other sizes
 574  */
 575 
 576 #define HDR_SIZE ((int64_t)sizeof (arc_buf_hdr_t))
 577 #define L2HDR_SIZE ((int64_t)sizeof (l2arc_buf_hdr_t))
 578 
 579 /*
 580  * Hash table routines
 581  */
 582 
 583 #define HT_LOCK_PAD     64
 584 
 585 struct ht_lock {
 586         kmutex_t        ht_lock;
 587 #ifdef _KERNEL
 588         unsigned char   pad[(HT_LOCK_PAD - sizeof (kmutex_t))];
 589 #endif
 590 };
 591 
 592 #define BUF_LOCKS 256
 593 typedef struct buf_hash_table {
 594         uint64_t ht_mask;
 595         arc_buf_hdr_t **ht_table;
 596         struct ht_lock ht_locks[BUF_LOCKS];
 597 } buf_hash_table_t;
 598 
 599 static buf_hash_table_t buf_hash_table;
 600 
 601 #define BUF_HASH_INDEX(spa, dva, birth) \
 602         (buf_hash(spa, dva, birth) & buf_hash_table.ht_mask)
 603 #define BUF_HASH_LOCK_NTRY(idx) (buf_hash_table.ht_locks[idx & (BUF_LOCKS-1)])
 604 #define BUF_HASH_LOCK(idx)      (&(BUF_HASH_LOCK_NTRY(idx).ht_lock))
 605 #define HDR_LOCK(hdr) \
 606         (BUF_HASH_LOCK(BUF_HASH_INDEX(hdr->b_spa, &hdr->b_dva, hdr->b_birth)))
 607 
 608 uint64_t zfs_crc64_table[256];
 609 
 610 /*
 611  * Level 2 ARC
 612  */
 613 
 614 #define L2ARC_WRITE_SIZE        (8 * 1024 * 1024)       /* initial write max */
 615 #define L2ARC_HEADROOM          2                       /* num of writes */
 616 /*
 617  * If we discover during ARC scan any buffers to be compressed, we boost
 618  * our headroom for the next scanning cycle by this percentage multiple.
 619  */
 620 #define L2ARC_HEADROOM_BOOST    200
 621 #define L2ARC_FEED_SECS         1               /* caching interval secs */
 622 #define L2ARC_FEED_MIN_MS       200             /* min caching interval ms */
 623 
 624 #define l2arc_writes_sent       ARCSTAT(arcstat_l2_writes_sent)
 625 #define l2arc_writes_done       ARCSTAT(arcstat_l2_writes_done)
 626 
 627 /* L2ARC Performance Tunables */
 628 uint64_t l2arc_write_max = L2ARC_WRITE_SIZE;    /* default max write size */
 629 uint64_t l2arc_write_boost = L2ARC_WRITE_SIZE;  /* extra write during warmup */
 630 uint64_t l2arc_headroom = L2ARC_HEADROOM;       /* number of dev writes */
 631 uint64_t l2arc_headroom_boost = L2ARC_HEADROOM_BOOST;
 632 uint64_t l2arc_feed_secs = L2ARC_FEED_SECS;     /* interval seconds */
 633 uint64_t l2arc_feed_min_ms = L2ARC_FEED_MIN_MS; /* min interval milliseconds */
 634 boolean_t l2arc_noprefetch = B_TRUE;            /* don't cache prefetch bufs */
 635 boolean_t l2arc_feed_again = B_TRUE;            /* turbo warmup */
 636 boolean_t l2arc_norw = B_TRUE;                  /* no reads during writes */
 637 
 638 /*
 639  * L2ARC Internals
 640  */
 641 typedef struct l2arc_dev {
 642         vdev_t                  *l2ad_vdev;     /* vdev */
 643         spa_t                   *l2ad_spa;      /* spa */
 644         uint64_t                l2ad_hand;      /* next write location */
 645         uint64_t                l2ad_start;     /* first addr on device */
 646         uint64_t                l2ad_end;       /* last addr on device */
 647         uint64_t                l2ad_evict;     /* last addr eviction reached */
 648         boolean_t               l2ad_first;     /* first sweep through */
 649         boolean_t               l2ad_writing;   /* currently writing */
 650         list_t                  *l2ad_buflist;  /* buffer list */
 651         list_node_t             l2ad_node;      /* device list node */
 652 } l2arc_dev_t;
 653 
 654 static list_t L2ARC_dev_list;                   /* device list */
 655 static list_t *l2arc_dev_list;                  /* device list pointer */
 656 static kmutex_t l2arc_dev_mtx;                  /* device list mutex */
 657 static l2arc_dev_t *l2arc_dev_last;             /* last device used */
 658 static kmutex_t l2arc_buflist_mtx;              /* mutex for all buflists */
 659 static list_t L2ARC_free_on_write;              /* free after write buf list */
 660 static list_t *l2arc_free_on_write;             /* free after write list ptr */
 661 static kmutex_t l2arc_free_on_write_mtx;        /* mutex for list */
 662 static uint64_t l2arc_ndev;                     /* number of devices */
 663 
 664 typedef struct l2arc_read_callback {
 665         arc_buf_t               *l2rcb_buf;             /* read buffer */
 666         spa_t                   *l2rcb_spa;             /* spa */
 667         blkptr_t                l2rcb_bp;               /* original blkptr */
 668         zbookmark_phys_t        l2rcb_zb;               /* original bookmark */
 669         int                     l2rcb_flags;            /* original flags */
 670         enum zio_compress       l2rcb_compress;         /* applied compress */
 671 } l2arc_read_callback_t;
 672 
 673 typedef struct l2arc_write_callback {
 674         l2arc_dev_t     *l2wcb_dev;             /* device info */
 675         arc_buf_hdr_t   *l2wcb_head;            /* head of write buflist */
 676 } l2arc_write_callback_t;
 677 
 678 struct l2arc_buf_hdr {
 679         /* protected by arc_buf_hdr  mutex */
 680         l2arc_dev_t             *b_dev;         /* L2ARC device */
 681         uint64_t                b_daddr;        /* disk address, offset byte */
 682         /* compression applied to buffer data */
 683         enum zio_compress       b_compress;
 684         /* real alloc'd buffer size depending on b_compress applied */
 685         int                     b_asize;
 686         /* temporary buffer holder for in-flight compressed data */
 687         void                    *b_tmp_cdata;
 688 };
 689 
 690 typedef struct l2arc_data_free {
 691         /* protected by l2arc_free_on_write_mtx */
 692         void            *l2df_data;
 693         size_t          l2df_size;
 694         void            (*l2df_func)(void *, size_t);
 695         list_node_t     l2df_list_node;
 696 } l2arc_data_free_t;
 697 
 698 static kmutex_t l2arc_feed_thr_lock;
 699 static kcondvar_t l2arc_feed_thr_cv;
 700 static uint8_t l2arc_thread_exit;
 701 
 702 static void l2arc_read_done(zio_t *zio);
 703 static void l2arc_hdr_stat_add(void);
 704 static void l2arc_hdr_stat_remove(void);
 705 
 706 static boolean_t l2arc_compress_buf(l2arc_buf_hdr_t *l2hdr);
 707 static void l2arc_decompress_zio(zio_t *zio, arc_buf_hdr_t *hdr,
 708     enum zio_compress c);
 709 static void l2arc_release_cdata_buf(arc_buf_hdr_t *ab);
 710 
 711 static uint64_t
 712 buf_hash(uint64_t spa, const dva_t *dva, uint64_t birth)
 713 {
 714         uint8_t *vdva = (uint8_t *)dva;
 715         uint64_t crc = -1ULL;
 716         int i;
 717 
 718         ASSERT(zfs_crc64_table[128] == ZFS_CRC64_POLY);
 719 
 720         for (i = 0; i < sizeof (dva_t); i++)
 721                 crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ vdva[i]) & 0xFF];
 722 
 723         crc ^= (spa>>8) ^ birth;
 724 
 725         return (crc);
 726 }
 727 
 728 #define BUF_EMPTY(buf)                                          \
 729         ((buf)->b_dva.dva_word[0] == 0 &&                    \
 730         (buf)->b_dva.dva_word[1] == 0 &&                     \
 731         (buf)->b_cksum0 == 0)
 732 
 733 #define BUF_EQUAL(spa, dva, birth, buf)                         \
 734         ((buf)->b_dva.dva_word[0] == (dva)->dva_word[0]) &&       \
 735         ((buf)->b_dva.dva_word[1] == (dva)->dva_word[1]) &&       \
 736         ((buf)->b_birth == birth) && ((buf)->b_spa == spa)
 737 
 738 static void
 739 buf_discard_identity(arc_buf_hdr_t *hdr)
 740 {
 741         hdr->b_dva.dva_word[0] = 0;
 742         hdr->b_dva.dva_word[1] = 0;
 743         hdr->b_birth = 0;
 744         hdr->b_cksum0 = 0;
 745 }
 746 
 747 static arc_buf_hdr_t *
 748 buf_hash_find(uint64_t spa, const blkptr_t *bp, kmutex_t **lockp)
 749 {
 750         const dva_t *dva = BP_IDENTITY(bp);
 751         uint64_t birth = BP_PHYSICAL_BIRTH(bp);
 752         uint64_t idx = BUF_HASH_INDEX(spa, dva, birth);
 753         kmutex_t *hash_lock = BUF_HASH_LOCK(idx);
 754         arc_buf_hdr_t *buf;
 755 
 756         mutex_enter(hash_lock);
 757         for (buf = buf_hash_table.ht_table[idx]; buf != NULL;
 758             buf = buf->b_hash_next) {
 759                 if (BUF_EQUAL(spa, dva, birth, buf)) {
 760                         *lockp = hash_lock;
 761                         return (buf);
 762                 }
 763         }
 764         mutex_exit(hash_lock);
 765         *lockp = NULL;
 766         return (NULL);
 767 }
 768 
 769 /*
 770  * Insert an entry into the hash table.  If there is already an element
 771  * equal to elem in the hash table, then the already existing element
 772  * will be returned and the new element will not be inserted.
 773  * Otherwise returns NULL.
 774  */
 775 static arc_buf_hdr_t *
 776 buf_hash_insert(arc_buf_hdr_t *buf, kmutex_t **lockp)
 777 {
 778         uint64_t idx = BUF_HASH_INDEX(buf->b_spa, &buf->b_dva, buf->b_birth);
 779         kmutex_t *hash_lock = BUF_HASH_LOCK(idx);
 780         arc_buf_hdr_t *fbuf;
 781         uint32_t i;
 782 
 783         ASSERT(!DVA_IS_EMPTY(&buf->b_dva));
 784         ASSERT(buf->b_birth != 0);
 785         ASSERT(!HDR_IN_HASH_TABLE(buf));
 786         *lockp = hash_lock;
 787         mutex_enter(hash_lock);
 788         for (fbuf = buf_hash_table.ht_table[idx], i = 0; fbuf != NULL;
 789             fbuf = fbuf->b_hash_next, i++) {
 790                 if (BUF_EQUAL(buf->b_spa, &buf->b_dva, buf->b_birth, fbuf))
 791                         return (fbuf);
 792         }
 793 
 794         buf->b_hash_next = buf_hash_table.ht_table[idx];
 795         buf_hash_table.ht_table[idx] = buf;
 796         buf->b_flags |= ARC_IN_HASH_TABLE;
 797 
 798         /* collect some hash table performance data */
 799         if (i > 0) {
 800                 ARCSTAT_BUMP(arcstat_hash_collisions);
 801                 if (i == 1)
 802                         ARCSTAT_BUMP(arcstat_hash_chains);
 803 
 804                 ARCSTAT_MAX(arcstat_hash_chain_max, i);
 805         }
 806 
 807         ARCSTAT_BUMP(arcstat_hash_elements);
 808         ARCSTAT_MAXSTAT(arcstat_hash_elements);
 809 
 810         return (NULL);
 811 }
 812 
 813 static void
 814 buf_hash_remove(arc_buf_hdr_t *buf)
 815 {
 816         arc_buf_hdr_t *fbuf, **bufp;
 817         uint64_t idx = BUF_HASH_INDEX(buf->b_spa, &buf->b_dva, buf->b_birth);
 818 
 819         ASSERT(MUTEX_HELD(BUF_HASH_LOCK(idx)));
 820         ASSERT(HDR_IN_HASH_TABLE(buf));
 821 
 822         bufp = &buf_hash_table.ht_table[idx];
 823         while ((fbuf = *bufp) != buf) {
 824                 ASSERT(fbuf != NULL);
 825                 bufp = &fbuf->b_hash_next;
 826         }
 827         *bufp = buf->b_hash_next;
 828         buf->b_hash_next = NULL;
 829         buf->b_flags &= ~ARC_IN_HASH_TABLE;
 830 
 831         /* collect some hash table performance data */
 832         ARCSTAT_BUMPDOWN(arcstat_hash_elements);
 833 
 834         if (buf_hash_table.ht_table[idx] &&
 835             buf_hash_table.ht_table[idx]->b_hash_next == NULL)
 836                 ARCSTAT_BUMPDOWN(arcstat_hash_chains);
 837 }
 838 
 839 /*
 840  * Global data structures and functions for the buf kmem cache.
 841  */
 842 static kmem_cache_t *hdr_cache;
 843 static kmem_cache_t *buf_cache;
 844 
 845 static void
 846 buf_fini(void)
 847 {
 848         int i;
 849 
 850         kmem_free(buf_hash_table.ht_table,
 851             (buf_hash_table.ht_mask + 1) * sizeof (void *));
 852         for (i = 0; i < BUF_LOCKS; i++)
 853                 mutex_destroy(&buf_hash_table.ht_locks[i].ht_lock);
 854         kmem_cache_destroy(hdr_cache);
 855         kmem_cache_destroy(buf_cache);
 856 }
 857 
 858 /*
 859  * Constructor callback - called when the cache is empty
 860  * and a new buf is requested.
 861  */
 862 /* ARGSUSED */
 863 static int
 864 hdr_cons(void *vbuf, void *unused, int kmflag)
 865 {
 866         arc_buf_hdr_t *buf = vbuf;
 867 
 868         bzero(buf, sizeof (arc_buf_hdr_t));
 869         refcount_create(&buf->b_refcnt);
 870         cv_init(&buf->b_cv, NULL, CV_DEFAULT, NULL);
 871         mutex_init(&buf->b_freeze_lock, NULL, MUTEX_DEFAULT, NULL);
 872         arc_space_consume(sizeof (arc_buf_hdr_t), ARC_SPACE_HDRS);
 873 
 874         return (0);
 875 }
 876 
 877 /* ARGSUSED */
 878 static int
 879 buf_cons(void *vbuf, void *unused, int kmflag)
 880 {
 881         arc_buf_t *buf = vbuf;
 882 
 883         bzero(buf, sizeof (arc_buf_t));
 884         mutex_init(&buf->b_evict_lock, NULL, MUTEX_DEFAULT, NULL);
 885         arc_space_consume(sizeof (arc_buf_t), ARC_SPACE_HDRS);
 886 
 887         return (0);
 888 }
 889 
 890 /*
 891  * Destructor callback - called when a cached buf is
 892  * no longer required.
 893  */
 894 /* ARGSUSED */
 895 static void
 896 hdr_dest(void *vbuf, void *unused)
 897 {
 898         arc_buf_hdr_t *buf = vbuf;
 899 
 900         ASSERT(BUF_EMPTY(buf));
 901         refcount_destroy(&buf->b_refcnt);
 902         cv_destroy(&buf->b_cv);
 903         mutex_destroy(&buf->b_freeze_lock);
 904         arc_space_return(sizeof (arc_buf_hdr_t), ARC_SPACE_HDRS);
 905 }
 906 
 907 /* ARGSUSED */
 908 static void
 909 buf_dest(void *vbuf, void *unused)
 910 {
 911         arc_buf_t *buf = vbuf;
 912 
 913         mutex_destroy(&buf->b_evict_lock);
 914         arc_space_return(sizeof (arc_buf_t), ARC_SPACE_HDRS);
 915 }
 916 
 917 /*
 918  * Reclaim callback -- invoked when memory is low.
 919  */
 920 /* ARGSUSED */
 921 static void
 922 hdr_recl(void *unused)
 923 {
 924         dprintf("hdr_recl called\n");
 925         /*
 926          * umem calls the reclaim func when we destroy the buf cache,
 927          * which is after we do arc_fini().
 928          */
 929         if (!arc_dead)
 930                 cv_signal(&arc_reclaim_thr_cv);
 931 }
 932 
 933 static void
 934 buf_init(void)
 935 {
 936         uint64_t *ct;
 937         uint64_t hsize = 1ULL << 12;
 938         int i, j;
 939 
 940         /*
 941          * The hash table is big enough to fill all of physical memory
 942          * with an average block size of zfs_arc_average_blocksize (default 8K).
 943          * By default, the table will take up
 944          * totalmem * sizeof(void*) / 8K (1MB per GB with 8-byte pointers).
 945          */
 946         while (hsize * zfs_arc_average_blocksize < physmem * PAGESIZE)
 947                 hsize <<= 1;
 948 retry:
 949         buf_hash_table.ht_mask = hsize - 1;
 950         buf_hash_table.ht_table =
 951             kmem_zalloc(hsize * sizeof (void*), KM_NOSLEEP);
 952         if (buf_hash_table.ht_table == NULL) {
 953                 ASSERT(hsize > (1ULL << 8));
 954                 hsize >>= 1;
 955                 goto retry;
 956         }
 957 
 958         hdr_cache = kmem_cache_create("arc_buf_hdr_t", sizeof (arc_buf_hdr_t),
 959             0, hdr_cons, hdr_dest, hdr_recl, NULL, NULL, 0);
 960         buf_cache = kmem_cache_create("arc_buf_t", sizeof (arc_buf_t),
 961             0, buf_cons, buf_dest, NULL, NULL, NULL, 0);
 962 
 963         for (i = 0; i < 256; i++)
 964                 for (ct = zfs_crc64_table + i, *ct = i, j = 8; j > 0; j--)
 965                         *ct = (*ct >> 1) ^ (-(*ct & 1) & ZFS_CRC64_POLY);
 966 
 967         for (i = 0; i < BUF_LOCKS; i++) {
 968                 mutex_init(&buf_hash_table.ht_locks[i].ht_lock,
 969                     NULL, MUTEX_DEFAULT, NULL);
 970         }
 971 }
 972 
 973 #define ARC_MINTIME     (hz>>4) /* 62 ms */
 974 
 975 static void
 976 arc_cksum_verify(arc_buf_t *buf)
 977 {
 978         zio_cksum_t zc;
 979 
 980         if (!(zfs_flags & ZFS_DEBUG_MODIFY))
 981                 return;
 982 
 983         mutex_enter(&buf->b_hdr->b_freeze_lock);
 984         if (buf->b_hdr->b_freeze_cksum == NULL ||
 985             (buf->b_hdr->b_flags & ARC_IO_ERROR)) {
 986                 mutex_exit(&buf->b_hdr->b_freeze_lock);
 987                 return;
 988         }
 989         fletcher_2_native(buf->b_data, buf->b_hdr->b_size, &zc);
 990         if (!ZIO_CHECKSUM_EQUAL(*buf->b_hdr->b_freeze_cksum, zc))
 991                 panic("buffer modified while frozen!");
 992         mutex_exit(&buf->b_hdr->b_freeze_lock);
 993 }
 994 
 995 static int
 996 arc_cksum_equal(arc_buf_t *buf)
 997 {
 998         zio_cksum_t zc;
 999         int equal;
1000 
1001         mutex_enter(&buf->b_hdr->b_freeze_lock);
1002         fletcher_2_native(buf->b_data, buf->b_hdr->b_size, &zc);
1003         equal = ZIO_CHECKSUM_EQUAL(*buf->b_hdr->b_freeze_cksum, zc);
1004         mutex_exit(&buf->b_hdr->b_freeze_lock);
1005 
1006         return (equal);
1007 }
1008 
1009 static void
1010 arc_cksum_compute(arc_buf_t *buf, boolean_t force)
1011 {
1012         if (!force && !(zfs_flags & ZFS_DEBUG_MODIFY))
1013                 return;
1014 
1015         mutex_enter(&buf->b_hdr->b_freeze_lock);
1016         if (buf->b_hdr->b_freeze_cksum != NULL) {
1017                 mutex_exit(&buf->b_hdr->b_freeze_lock);
1018                 return;
1019         }
1020         buf->b_hdr->b_freeze_cksum = kmem_alloc(sizeof (zio_cksum_t), KM_SLEEP);
1021         fletcher_2_native(buf->b_data, buf->b_hdr->b_size,
1022             buf->b_hdr->b_freeze_cksum);
1023         mutex_exit(&buf->b_hdr->b_freeze_lock);
1024         arc_buf_watch(buf);
1025 }
1026 
1027 #ifndef _KERNEL
1028 typedef struct procctl {
1029         long cmd;
1030         prwatch_t prwatch;
1031 } procctl_t;
1032 #endif
1033 
1034 /* ARGSUSED */
1035 static void
1036 arc_buf_unwatch(arc_buf_t *buf)
1037 {
1038 #ifndef _KERNEL
1039         if (arc_watch) {
1040                 int result;
1041                 procctl_t ctl;
1042                 ctl.cmd = PCWATCH;
1043                 ctl.prwatch.pr_vaddr = (uintptr_t)buf->b_data;
1044                 ctl.prwatch.pr_size = 0;
1045                 ctl.prwatch.pr_wflags = 0;
1046                 result = write(arc_procfd, &ctl, sizeof (ctl));
1047                 ASSERT3U(result, ==, sizeof (ctl));
1048         }
1049 #endif
1050 }
1051 
1052 /* ARGSUSED */
1053 static void
1054 arc_buf_watch(arc_buf_t *buf)
1055 {
1056 #ifndef _KERNEL
1057         if (arc_watch) {
1058                 int result;
1059                 procctl_t ctl;
1060                 ctl.cmd = PCWATCH;
1061                 ctl.prwatch.pr_vaddr = (uintptr_t)buf->b_data;
1062                 ctl.prwatch.pr_size = buf->b_hdr->b_size;
1063                 ctl.prwatch.pr_wflags = WA_WRITE;
1064                 result = write(arc_procfd, &ctl, sizeof (ctl));
1065                 ASSERT3U(result, ==, sizeof (ctl));
1066         }
1067 #endif
1068 }
1069 
1070 void
1071 arc_buf_thaw(arc_buf_t *buf)
1072 {
1073         if (zfs_flags & ZFS_DEBUG_MODIFY) {
1074                 if (buf->b_hdr->b_state != arc_anon)
1075                         panic("modifying non-anon buffer!");
1076                 if (buf->b_hdr->b_flags & ARC_IO_IN_PROGRESS)
1077                         panic("modifying buffer while i/o in progress!");
1078                 arc_cksum_verify(buf);
1079         }
1080 
1081         mutex_enter(&buf->b_hdr->b_freeze_lock);
1082         if (buf->b_hdr->b_freeze_cksum != NULL) {
1083                 kmem_free(buf->b_hdr->b_freeze_cksum, sizeof (zio_cksum_t));
1084                 buf->b_hdr->b_freeze_cksum = NULL;
1085         }
1086 
1087         if (zfs_flags & ZFS_DEBUG_MODIFY) {
1088                 if (buf->b_hdr->b_thawed)
1089                         kmem_free(buf->b_hdr->b_thawed, 1);
1090                 buf->b_hdr->b_thawed = kmem_alloc(1, KM_SLEEP);
1091         }
1092 
1093         mutex_exit(&buf->b_hdr->b_freeze_lock);
1094 
1095         arc_buf_unwatch(buf);
1096 }
1097 
1098 void
1099 arc_buf_freeze(arc_buf_t *buf)
1100 {
1101         kmutex_t *hash_lock;
1102 
1103         if (!(zfs_flags & ZFS_DEBUG_MODIFY))
1104                 return;
1105 
1106         hash_lock = HDR_LOCK(buf->b_hdr);
1107         mutex_enter(hash_lock);
1108 
1109         ASSERT(buf->b_hdr->b_freeze_cksum != NULL ||
1110             buf->b_hdr->b_state == arc_anon);
1111         arc_cksum_compute(buf, B_FALSE);
1112         mutex_exit(hash_lock);
1113 
1114 }
1115 
1116 static void
1117 add_reference(arc_buf_hdr_t *ab, kmutex_t *hash_lock, void *tag)
1118 {
1119         ASSERT(MUTEX_HELD(hash_lock));
1120 
1121         if ((refcount_add(&ab->b_refcnt, tag) == 1) &&
1122             (ab->b_state != arc_anon)) {
1123                 uint64_t delta = ab->b_size * ab->b_datacnt;
1124                 list_t *list = &ab->b_state->arcs_list[ab->b_type];
1125                 uint64_t *size = &ab->b_state->arcs_lsize[ab->b_type];
1126 
1127                 ASSERT(!MUTEX_HELD(&ab->b_state->arcs_mtx));
1128                 mutex_enter(&ab->b_state->arcs_mtx);
1129                 ASSERT(list_link_active(&ab->b_arc_node));
1130                 list_remove(list, ab);
1131                 if (GHOST_STATE(ab->b_state)) {
1132                         ASSERT0(ab->b_datacnt);
1133                         ASSERT3P(ab->b_buf, ==, NULL);
1134                         delta = ab->b_size;
1135                 }
1136                 ASSERT(delta > 0);
1137                 ASSERT3U(*size, >=, delta);
1138                 atomic_add_64(size, -delta);
1139                 mutex_exit(&ab->b_state->arcs_mtx);
1140                 /* remove the prefetch flag if we get a reference */
1141                 if (ab->b_flags & ARC_PREFETCH)
1142                         ab->b_flags &= ~ARC_PREFETCH;
1143         }
1144 }
1145 
1146 static int
1147 remove_reference(arc_buf_hdr_t *ab, kmutex_t *hash_lock, void *tag)
1148 {
1149         int cnt;
1150         arc_state_t *state = ab->b_state;
1151 
1152         ASSERT(state == arc_anon || MUTEX_HELD(hash_lock));
1153         ASSERT(!GHOST_STATE(state));
1154 
1155         if (((cnt = refcount_remove(&ab->b_refcnt, tag)) == 0) &&
1156             (state != arc_anon)) {
1157                 uint64_t *size = &state->arcs_lsize[ab->b_type];
1158 
1159                 ASSERT(!MUTEX_HELD(&state->arcs_mtx));
1160                 mutex_enter(&state->arcs_mtx);
1161                 ASSERT(!list_link_active(&ab->b_arc_node));
1162                 list_insert_head(&state->arcs_list[ab->b_type], ab);
1163                 ASSERT(ab->b_datacnt > 0);
1164                 atomic_add_64(size, ab->b_size * ab->b_datacnt);
1165                 mutex_exit(&state->arcs_mtx);
1166         }
1167         return (cnt);
1168 }
1169 
1170 /*
1171  * Move the supplied buffer to the indicated state.  The mutex
1172  * for the buffer must be held by the caller.
1173  */
1174 static void
1175 arc_change_state(arc_state_t *new_state, arc_buf_hdr_t *ab, kmutex_t *hash_lock)
1176 {
1177         arc_state_t *old_state = ab->b_state;
1178         int64_t refcnt = refcount_count(&ab->b_refcnt);
1179         uint64_t from_delta, to_delta;
1180 
1181         ASSERT(MUTEX_HELD(hash_lock));
1182         ASSERT3P(new_state, !=, old_state);
1183         ASSERT(refcnt == 0 || ab->b_datacnt > 0);
1184         ASSERT(ab->b_datacnt == 0 || !GHOST_STATE(new_state));
1185         ASSERT(ab->b_datacnt <= 1 || old_state != arc_anon);
1186 
1187         from_delta = to_delta = ab->b_datacnt * ab->b_size;
1188 
1189         /*
1190          * If this buffer is evictable, transfer it from the
1191          * old state list to the new state list.
1192          */
1193         if (refcnt == 0) {
1194                 if (old_state != arc_anon) {
1195                         int use_mutex = !MUTEX_HELD(&old_state->arcs_mtx);
1196                         uint64_t *size = &old_state->arcs_lsize[ab->b_type];
1197 
1198                         if (use_mutex)
1199                                 mutex_enter(&old_state->arcs_mtx);
1200 
1201                         ASSERT(list_link_active(&ab->b_arc_node));
1202                         list_remove(&old_state->arcs_list[ab->b_type], ab);
1203 
1204                         /*
1205                          * If prefetching out of the ghost cache,
1206                          * we will have a non-zero datacnt.
1207                          */
1208                         if (GHOST_STATE(old_state) && ab->b_datacnt == 0) {
1209                                 /* ghost elements have a ghost size */
1210                                 ASSERT(ab->b_buf == NULL);
1211                                 from_delta = ab->b_size;
1212                         }
1213                         ASSERT3U(*size, >=, from_delta);
1214                         atomic_add_64(size, -from_delta);
1215 
1216                         if (use_mutex)
1217                                 mutex_exit(&old_state->arcs_mtx);
1218                 }
1219                 if (new_state != arc_anon) {
1220                         int use_mutex = !MUTEX_HELD(&new_state->arcs_mtx);
1221                         uint64_t *size = &new_state->arcs_lsize[ab->b_type];
1222 
1223                         if (use_mutex)
1224                                 mutex_enter(&new_state->arcs_mtx);
1225 
1226                         list_insert_head(&new_state->arcs_list[ab->b_type], ab);
1227 
1228                         /* ghost elements have a ghost size */
1229                         if (GHOST_STATE(new_state)) {
1230                                 ASSERT(ab->b_datacnt == 0);
1231                                 ASSERT(ab->b_buf == NULL);
1232                                 to_delta = ab->b_size;
1233                         }
1234                         atomic_add_64(size, to_delta);
1235 
1236                         if (use_mutex)
1237                                 mutex_exit(&new_state->arcs_mtx);
1238                 }
1239         }
1240 
1241         ASSERT(!BUF_EMPTY(ab));
1242         if (new_state == arc_anon && HDR_IN_HASH_TABLE(ab))
1243                 buf_hash_remove(ab);
1244 
1245         /* adjust state sizes */
1246         if (to_delta)
1247                 atomic_add_64(&new_state->arcs_size, to_delta);
1248         if (from_delta) {
1249                 ASSERT3U(old_state->arcs_size, >=, from_delta);
1250                 atomic_add_64(&old_state->arcs_size, -from_delta);
1251         }
1252         ab->b_state = new_state;
1253 
1254         /* adjust l2arc hdr stats */
1255         if (new_state == arc_l2c_only)
1256                 l2arc_hdr_stat_add();
1257         else if (old_state == arc_l2c_only)
1258                 l2arc_hdr_stat_remove();
1259 }
1260 
1261 void
1262 arc_space_consume(uint64_t space, arc_space_type_t type)
1263 {
1264         ASSERT(type >= 0 && type < ARC_SPACE_NUMTYPES);
1265 
1266         switch (type) {
1267         case ARC_SPACE_DATA:
1268                 ARCSTAT_INCR(arcstat_data_size, space);
1269                 break;
1270         case ARC_SPACE_OTHER:
1271                 ARCSTAT_INCR(arcstat_other_size, space);
1272                 break;
1273         case ARC_SPACE_HDRS:
1274                 ARCSTAT_INCR(arcstat_hdr_size, space);
1275                 break;
1276         case ARC_SPACE_L2HDRS:
1277                 ARCSTAT_INCR(arcstat_l2_hdr_size, space);
1278                 break;
1279         }
1280 
1281         ARCSTAT_INCR(arcstat_meta_used, space);
1282         atomic_add_64(&arc_size, space);
1283 }
1284 
1285 void
1286 arc_space_return(uint64_t space, arc_space_type_t type)
1287 {
1288         ASSERT(type >= 0 && type < ARC_SPACE_NUMTYPES);
1289 
1290         switch (type) {
1291         case ARC_SPACE_DATA:
1292                 ARCSTAT_INCR(arcstat_data_size, -space);
1293                 break;
1294         case ARC_SPACE_OTHER:
1295                 ARCSTAT_INCR(arcstat_other_size, -space);
1296                 break;
1297         case ARC_SPACE_HDRS:
1298                 ARCSTAT_INCR(arcstat_hdr_size, -space);
1299                 break;
1300         case ARC_SPACE_L2HDRS:
1301                 ARCSTAT_INCR(arcstat_l2_hdr_size, -space);
1302                 break;
1303         }
1304 
1305         ASSERT(arc_meta_used >= space);
1306         if (arc_meta_max < arc_meta_used)
1307                 arc_meta_max = arc_meta_used;
1308         ARCSTAT_INCR(arcstat_meta_used, -space);
1309         ASSERT(arc_size >= space);
1310         atomic_add_64(&arc_size, -space);
1311 }
1312 
1313 void *
1314 arc_data_buf_alloc(uint64_t size)
1315 {
1316         if (arc_evict_needed(ARC_BUFC_DATA))
1317                 cv_signal(&arc_reclaim_thr_cv);
1318         atomic_add_64(&arc_size, size);
1319         return (zio_data_buf_alloc(size));
1320 }
1321 
1322 void
1323 arc_data_buf_free(void *buf, uint64_t size)
1324 {
1325         zio_data_buf_free(buf, size);
1326         ASSERT(arc_size >= size);
1327         atomic_add_64(&arc_size, -size);
1328 }
1329 
1330 arc_buf_t *
1331 arc_buf_alloc(spa_t *spa, int size, void *tag, arc_buf_contents_t type)
1332 {
1333         arc_buf_hdr_t *hdr;
1334         arc_buf_t *buf;
1335 
1336         ASSERT3U(size, >, 0);
1337         hdr = kmem_cache_alloc(hdr_cache, KM_PUSHPAGE);
1338         ASSERT(BUF_EMPTY(hdr));
1339         hdr->b_size = size;
1340         hdr->b_type = type;
1341         hdr->b_spa = spa_load_guid(spa);
1342         hdr->b_state = arc_anon;
1343         hdr->b_arc_access = 0;
1344         buf = kmem_cache_alloc(buf_cache, KM_PUSHPAGE);
1345         buf->b_hdr = hdr;
1346         buf->b_data = NULL;
1347         buf->b_efunc = NULL;
1348         buf->b_private = NULL;
1349         buf->b_next = NULL;
1350         hdr->b_buf = buf;
1351         arc_get_data_buf(buf);
1352         hdr->b_datacnt = 1;
1353         hdr->b_flags = 0;
1354         ASSERT(refcount_is_zero(&hdr->b_refcnt));
1355         (void) refcount_add(&hdr->b_refcnt, tag);
1356 
1357         return (buf);
1358 }
1359 
1360 static char *arc_onloan_tag = "onloan";
1361 
1362 /*
1363  * Loan out an anonymous arc buffer. Loaned buffers are not counted as in
1364  * flight data by arc_tempreserve_space() until they are "returned". Loaned
1365  * buffers must be returned to the arc before they can be used by the DMU or
1366  * freed.
1367  */
1368 arc_buf_t *
1369 arc_loan_buf(spa_t *spa, int size)
1370 {
1371         arc_buf_t *buf;
1372 
1373         buf = arc_buf_alloc(spa, size, arc_onloan_tag, ARC_BUFC_DATA);
1374 
1375         atomic_add_64(&arc_loaned_bytes, size);
1376         return (buf);
1377 }
1378 
1379 /*
1380  * Return a loaned arc buffer to the arc.
1381  */
1382 void
1383 arc_return_buf(arc_buf_t *buf, void *tag)
1384 {
1385         arc_buf_hdr_t *hdr = buf->b_hdr;
1386 
1387         ASSERT(buf->b_data != NULL);
1388         (void) refcount_add(&hdr->b_refcnt, tag);
1389         (void) refcount_remove(&hdr->b_refcnt, arc_onloan_tag);
1390 
1391         atomic_add_64(&arc_loaned_bytes, -hdr->b_size);
1392 }
1393 
1394 /* Detach an arc_buf from a dbuf (tag) */
1395 void
1396 arc_loan_inuse_buf(arc_buf_t *buf, void *tag)
1397 {
1398         arc_buf_hdr_t *hdr;
1399 
1400         ASSERT(buf->b_data != NULL);
1401         hdr = buf->b_hdr;
1402         (void) refcount_add(&hdr->b_refcnt, arc_onloan_tag);
1403         (void) refcount_remove(&hdr->b_refcnt, tag);
1404         buf->b_efunc = NULL;
1405         buf->b_private = NULL;
1406 
1407         atomic_add_64(&arc_loaned_bytes, hdr->b_size);
1408 }
1409 
1410 static arc_buf_t *
1411 arc_buf_clone(arc_buf_t *from)
1412 {
1413         arc_buf_t *buf;
1414         arc_buf_hdr_t *hdr = from->b_hdr;
1415         uint64_t size = hdr->b_size;
1416 
1417         ASSERT(hdr->b_state != arc_anon);
1418 
1419         buf = kmem_cache_alloc(buf_cache, KM_PUSHPAGE);
1420         buf->b_hdr = hdr;
1421         buf->b_data = NULL;
1422         buf->b_efunc = NULL;
1423         buf->b_private = NULL;
1424         buf->b_next = hdr->b_buf;
1425         hdr->b_buf = buf;
1426         arc_get_data_buf(buf);
1427         bcopy(from->b_data, buf->b_data, size);
1428 
1429         /*
1430          * This buffer already exists in the arc so create a duplicate
1431          * copy for the caller.  If the buffer is associated with user data
1432          * then track the size and number of duplicates.  These stats will be
1433          * updated as duplicate buffers are created and destroyed.
1434          */
1435         if (hdr->b_type == ARC_BUFC_DATA) {
1436                 ARCSTAT_BUMP(arcstat_duplicate_buffers);
1437                 ARCSTAT_INCR(arcstat_duplicate_buffers_size, size);
1438         }
1439         hdr->b_datacnt += 1;
1440         return (buf);
1441 }
1442 
1443 void
1444 arc_buf_add_ref(arc_buf_t *buf, void* tag)
1445 {
1446         arc_buf_hdr_t *hdr;
1447         kmutex_t *hash_lock;
1448 
1449         /*
1450          * Check to see if this buffer is evicted.  Callers
1451          * must verify b_data != NULL to know if the add_ref
1452          * was successful.
1453          */
1454         mutex_enter(&buf->b_evict_lock);
1455         if (buf->b_data == NULL) {
1456                 mutex_exit(&buf->b_evict_lock);
1457                 return;
1458         }
1459         hash_lock = HDR_LOCK(buf->b_hdr);
1460         mutex_enter(hash_lock);
1461         hdr = buf->b_hdr;
1462         ASSERT3P(hash_lock, ==, HDR_LOCK(hdr));
1463         mutex_exit(&buf->b_evict_lock);
1464 
1465         ASSERT(hdr->b_state == arc_mru || hdr->b_state == arc_mfu);
1466         add_reference(hdr, hash_lock, tag);
1467         DTRACE_PROBE1(arc__hit, arc_buf_hdr_t *, hdr);
1468         arc_access(hdr, hash_lock);
1469         mutex_exit(hash_lock);
1470         ARCSTAT_BUMP(arcstat_hits);
1471         ARCSTAT_CONDSTAT(!(hdr->b_flags & ARC_PREFETCH),
1472             demand, prefetch, hdr->b_type != ARC_BUFC_METADATA,
1473             data, metadata, hits);
1474 }
1475 
1476 /*
1477  * Free the arc data buffer.  If it is an l2arc write in progress,
1478  * the buffer is placed on l2arc_free_on_write to be freed later.
1479  */
1480 static void
1481 arc_buf_data_free(arc_buf_t *buf, void (*free_func)(void *, size_t))
1482 {
1483         arc_buf_hdr_t *hdr = buf->b_hdr;
1484 
1485         if (HDR_L2_WRITING(hdr)) {
1486                 l2arc_data_free_t *df;
1487                 df = kmem_alloc(sizeof (l2arc_data_free_t), KM_SLEEP);
1488                 df->l2df_data = buf->b_data;
1489                 df->l2df_size = hdr->b_size;
1490                 df->l2df_func = free_func;
1491                 mutex_enter(&l2arc_free_on_write_mtx);
1492                 list_insert_head(l2arc_free_on_write, df);
1493                 mutex_exit(&l2arc_free_on_write_mtx);
1494                 ARCSTAT_BUMP(arcstat_l2_free_on_write);
1495         } else {
1496                 free_func(buf->b_data, hdr->b_size);
1497         }
1498 }
1499 
1500 /*
1501  * Free up buf->b_data and if 'remove' is set, then pull the
1502  * arc_buf_t off of the the arc_buf_hdr_t's list and free it.
1503  */
1504 static void
1505 arc_buf_destroy(arc_buf_t *buf, boolean_t recycle, boolean_t remove)
1506 {
1507         arc_buf_t **bufp;
1508 
1509         /* free up data associated with the buf */
1510         if (buf->b_data) {
1511                 arc_state_t *state = buf->b_hdr->b_state;
1512                 uint64_t size = buf->b_hdr->b_size;
1513                 arc_buf_contents_t type = buf->b_hdr->b_type;
1514 
1515                 arc_cksum_verify(buf);
1516                 arc_buf_unwatch(buf);
1517 
1518                 if (!recycle) {
1519                         if (type == ARC_BUFC_METADATA) {
1520                                 arc_buf_data_free(buf, zio_buf_free);
1521                                 arc_space_return(size, ARC_SPACE_DATA);
1522                         } else {
1523                                 ASSERT(type == ARC_BUFC_DATA);
1524                                 arc_buf_data_free(buf, zio_data_buf_free);
1525                                 ARCSTAT_INCR(arcstat_data_size, -size);
1526                                 atomic_add_64(&arc_size, -size);
1527                         }
1528                 }
1529                 if (list_link_active(&buf->b_hdr->b_arc_node)) {
1530                         uint64_t *cnt = &state->arcs_lsize[type];
1531 
1532                         ASSERT(refcount_is_zero(&buf->b_hdr->b_refcnt));
1533                         ASSERT(state != arc_anon);
1534 
1535                         ASSERT3U(*cnt, >=, size);
1536                         atomic_add_64(cnt, -size);
1537                 }
1538                 ASSERT3U(state->arcs_size, >=, size);
1539                 atomic_add_64(&state->arcs_size, -size);
1540                 buf->b_data = NULL;
1541 
1542                 /*
1543                  * If we're destroying a duplicate buffer make sure
1544                  * that the appropriate statistics are updated.
1545                  */
1546                 if (buf->b_hdr->b_datacnt > 1 &&
1547                     buf->b_hdr->b_type == ARC_BUFC_DATA) {
1548                         ARCSTAT_BUMPDOWN(arcstat_duplicate_buffers);
1549                         ARCSTAT_INCR(arcstat_duplicate_buffers_size, -size);
1550                 }
1551                 ASSERT(buf->b_hdr->b_datacnt > 0);
1552                 buf->b_hdr->b_datacnt -= 1;
1553         }
1554 
1555         /* only remove the buf if requested */
1556         if (!remove)
1557                 return;
1558 
1559         /* remove the buf from the hdr list */
1560         for (bufp = &buf->b_hdr->b_buf; *bufp != buf; bufp = &(*bufp)->b_next)
1561                 continue;
1562         *bufp = buf->b_next;
1563         buf->b_next = NULL;
1564 
1565         ASSERT(buf->b_efunc == NULL);
1566 
1567         /* clean up the buf */
1568         buf->b_hdr = NULL;
1569         kmem_cache_free(buf_cache, buf);
1570 }
1571 
1572 static void
1573 arc_hdr_destroy(arc_buf_hdr_t *hdr)
1574 {
1575         ASSERT(refcount_is_zero(&hdr->b_refcnt));
1576         ASSERT3P(hdr->b_state, ==, arc_anon);
1577         ASSERT(!HDR_IO_IN_PROGRESS(hdr));
1578         l2arc_buf_hdr_t *l2hdr = hdr->b_l2hdr;
1579 
1580         if (l2hdr != NULL) {
1581                 boolean_t buflist_held = MUTEX_HELD(&l2arc_buflist_mtx);
1582                 /*
1583                  * To prevent arc_free() and l2arc_evict() from
1584                  * attempting to free the same buffer at the same time,
1585                  * a FREE_IN_PROGRESS flag is given to arc_free() to
1586                  * give it priority.  l2arc_evict() can't destroy this
1587                  * header while we are waiting on l2arc_buflist_mtx.
1588                  *
1589                  * The hdr may be removed from l2ad_buflist before we
1590                  * grab l2arc_buflist_mtx, so b_l2hdr is rechecked.
1591                  */
1592                 if (!buflist_held) {
1593                         mutex_enter(&l2arc_buflist_mtx);
1594                         l2hdr = hdr->b_l2hdr;
1595                 }
1596 
1597                 if (l2hdr != NULL) {
1598                         list_remove(l2hdr->b_dev->l2ad_buflist, hdr);
1599                         ARCSTAT_INCR(arcstat_l2_size, -hdr->b_size);
1600                         ARCSTAT_INCR(arcstat_l2_asize, -l2hdr->b_asize);
1601                         vdev_space_update(l2hdr->b_dev->l2ad_vdev,
1602                             -l2hdr->b_asize, 0, 0);
1603                         kmem_free(l2hdr, sizeof (l2arc_buf_hdr_t));
1604                         if (hdr->b_state == arc_l2c_only)
1605                                 l2arc_hdr_stat_remove();
1606                         hdr->b_l2hdr = NULL;
1607                 }
1608 
1609                 if (!buflist_held)
1610                         mutex_exit(&l2arc_buflist_mtx);
1611         }
1612 
1613         if (!BUF_EMPTY(hdr)) {
1614                 ASSERT(!HDR_IN_HASH_TABLE(hdr));
1615                 buf_discard_identity(hdr);
1616         }
1617         while (hdr->b_buf) {
1618                 arc_buf_t *buf = hdr->b_buf;
1619 
1620                 if (buf->b_efunc) {
1621                         mutex_enter(&arc_eviction_mtx);
1622                         mutex_enter(&buf->b_evict_lock);
1623                         ASSERT(buf->b_hdr != NULL);
1624                         arc_buf_destroy(hdr->b_buf, FALSE, FALSE);
1625                         hdr->b_buf = buf->b_next;
1626                         buf->b_hdr = &arc_eviction_hdr;
1627                         buf->b_next = arc_eviction_list;
1628                         arc_eviction_list = buf;
1629                         mutex_exit(&buf->b_evict_lock);
1630                         mutex_exit(&arc_eviction_mtx);
1631                 } else {
1632                         arc_buf_destroy(hdr->b_buf, FALSE, TRUE);
1633                 }
1634         }
1635         if (hdr->b_freeze_cksum != NULL) {
1636                 kmem_free(hdr->b_freeze_cksum, sizeof (zio_cksum_t));
1637                 hdr->b_freeze_cksum = NULL;
1638         }
1639         if (hdr->b_thawed) {
1640                 kmem_free(hdr->b_thawed, 1);
1641                 hdr->b_thawed = NULL;
1642         }
1643 
1644         ASSERT(!list_link_active(&hdr->b_arc_node));
1645         ASSERT3P(hdr->b_hash_next, ==, NULL);
1646         ASSERT3P(hdr->b_acb, ==, NULL);
1647         kmem_cache_free(hdr_cache, hdr);
1648 }
1649 
1650 void
1651 arc_buf_free(arc_buf_t *buf, void *tag)
1652 {
1653         arc_buf_hdr_t *hdr = buf->b_hdr;
1654         int hashed = hdr->b_state != arc_anon;
1655 
1656         ASSERT(buf->b_efunc == NULL);
1657         ASSERT(buf->b_data != NULL);
1658 
1659         if (hashed) {
1660                 kmutex_t *hash_lock = HDR_LOCK(hdr);
1661 
1662                 mutex_enter(hash_lock);
1663                 hdr = buf->b_hdr;
1664                 ASSERT3P(hash_lock, ==, HDR_LOCK(hdr));
1665 
1666                 (void) remove_reference(hdr, hash_lock, tag);
1667                 if (hdr->b_datacnt > 1) {
1668                         arc_buf_destroy(buf, FALSE, TRUE);
1669                 } else {
1670                         ASSERT(buf == hdr->b_buf);
1671                         ASSERT(buf->b_efunc == NULL);
1672                         hdr->b_flags |= ARC_BUF_AVAILABLE;
1673                 }
1674                 mutex_exit(hash_lock);
1675         } else if (HDR_IO_IN_PROGRESS(hdr)) {
1676                 int destroy_hdr;
1677                 /*
1678                  * We are in the middle of an async write.  Don't destroy
1679                  * this buffer unless the write completes before we finish
1680                  * decrementing the reference count.
1681                  */
1682                 mutex_enter(&arc_eviction_mtx);
1683                 (void) remove_reference(hdr, NULL, tag);
1684                 ASSERT(refcount_is_zero(&hdr->b_refcnt));
1685                 destroy_hdr = !HDR_IO_IN_PROGRESS(hdr);
1686                 mutex_exit(&arc_eviction_mtx);
1687                 if (destroy_hdr)
1688                         arc_hdr_destroy(hdr);
1689         } else {
1690                 if (remove_reference(hdr, NULL, tag) > 0)
1691                         arc_buf_destroy(buf, FALSE, TRUE);
1692                 else
1693                         arc_hdr_destroy(hdr);
1694         }
1695 }
1696 
1697 boolean_t
1698 arc_buf_remove_ref(arc_buf_t *buf, void* tag)
1699 {
1700         arc_buf_hdr_t *hdr = buf->b_hdr;
1701         kmutex_t *hash_lock = HDR_LOCK(hdr);
1702         boolean_t no_callback = (buf->b_efunc == NULL);
1703 
1704         if (hdr->b_state == arc_anon) {
1705                 ASSERT(hdr->b_datacnt == 1);
1706                 arc_buf_free(buf, tag);
1707                 return (no_callback);
1708         }
1709 
1710         mutex_enter(hash_lock);
1711         hdr = buf->b_hdr;
1712         ASSERT3P(hash_lock, ==, HDR_LOCK(hdr));
1713         ASSERT(hdr->b_state != arc_anon);
1714         ASSERT(buf->b_data != NULL);
1715 
1716         (void) remove_reference(hdr, hash_lock, tag);
1717         if (hdr->b_datacnt > 1) {
1718                 if (no_callback)
1719                         arc_buf_destroy(buf, FALSE, TRUE);
1720         } else if (no_callback) {
1721                 ASSERT(hdr->b_buf == buf && buf->b_next == NULL);
1722                 ASSERT(buf->b_efunc == NULL);
1723                 hdr->b_flags |= ARC_BUF_AVAILABLE;
1724         }
1725         ASSERT(no_callback || hdr->b_datacnt > 1 ||
1726             refcount_is_zero(&hdr->b_refcnt));
1727         mutex_exit(hash_lock);
1728         return (no_callback);
1729 }
1730 
1731 int
1732 arc_buf_size(arc_buf_t *buf)
1733 {
1734         return (buf->b_hdr->b_size);
1735 }
1736 
1737 /*
1738  * Called from the DMU to determine if the current buffer should be
1739  * evicted. In order to ensure proper locking, the eviction must be initiated
1740  * from the DMU. Return true if the buffer is associated with user data and
1741  * duplicate buffers still exist.
1742  */
1743 boolean_t
1744 arc_buf_eviction_needed(arc_buf_t *buf)
1745 {
1746         arc_buf_hdr_t *hdr;
1747         boolean_t evict_needed = B_FALSE;
1748 
1749         if (zfs_disable_dup_eviction)
1750                 return (B_FALSE);
1751 
1752         mutex_enter(&buf->b_evict_lock);
1753         hdr = buf->b_hdr;
1754         if (hdr == NULL) {
1755                 /*
1756                  * We are in arc_do_user_evicts(); let that function
1757                  * perform the eviction.
1758                  */
1759                 ASSERT(buf->b_data == NULL);
1760                 mutex_exit(&buf->b_evict_lock);
1761                 return (B_FALSE);
1762         } else if (buf->b_data == NULL) {
1763                 /*
1764                  * We have already been added to the arc eviction list;
1765                  * recommend eviction.
1766                  */
1767                 ASSERT3P(hdr, ==, &arc_eviction_hdr);
1768                 mutex_exit(&buf->b_evict_lock);
1769                 return (B_TRUE);
1770         }
1771 
1772         if (hdr->b_datacnt > 1 && hdr->b_type == ARC_BUFC_DATA)
1773                 evict_needed = B_TRUE;
1774 
1775         mutex_exit(&buf->b_evict_lock);
1776         return (evict_needed);
1777 }
1778 
1779 /*
1780  * Evict buffers from list until we've removed the specified number of
1781  * bytes.  Move the removed buffers to the appropriate evict state.
1782  * If the recycle flag is set, then attempt to "recycle" a buffer:
1783  * - look for a buffer to evict that is `bytes' long.
1784  * - return the data block from this buffer rather than freeing it.
1785  * This flag is used by callers that are trying to make space for a
1786  * new buffer in a full arc cache.
1787  *
1788  * This function makes a "best effort".  It skips over any buffers
1789  * it can't get a hash_lock on, and so may not catch all candidates.
1790  * It may also return without evicting as much space as requested.
1791  */
1792 static void *
1793 arc_evict(arc_state_t *state, uint64_t spa, int64_t bytes, boolean_t recycle,
1794     arc_buf_contents_t type)
1795 {
1796         arc_state_t *evicted_state;
1797         uint64_t bytes_evicted = 0, skipped = 0, missed = 0;
1798         arc_buf_hdr_t *ab, *ab_prev = NULL;
1799         list_t *list = &state->arcs_list[type];
1800         kmutex_t *hash_lock;
1801         boolean_t have_lock;
1802         void *stolen = NULL;
1803         arc_buf_hdr_t marker = { 0 };
1804         int count = 0;
1805 
1806         ASSERT(state == arc_mru || state == arc_mfu);
1807 
1808         evicted_state = (state == arc_mru) ? arc_mru_ghost : arc_mfu_ghost;
1809 
1810         mutex_enter(&state->arcs_mtx);
1811         mutex_enter(&evicted_state->arcs_mtx);
1812 
1813         for (ab = list_tail(list); ab; ab = ab_prev) {
1814                 ab_prev = list_prev(list, ab);
1815                 /* prefetch buffers have a minimum lifespan */
1816                 if (HDR_IO_IN_PROGRESS(ab) ||
1817                     (spa && ab->b_spa != spa) ||
1818                     (ab->b_flags & (ARC_PREFETCH|ARC_INDIRECT) &&
1819                     ddi_get_lbolt() - ab->b_arc_access <
1820                     arc_min_prefetch_lifespan)) {
1821                         skipped++;
1822                         continue;
1823                 }
1824                 /* "lookahead" for better eviction candidate */
1825                 if (recycle && ab->b_size != bytes &&
1826                     ab_prev && ab_prev->b_size == bytes)
1827                         continue;
1828 
1829                 /* ignore markers */
1830                 if (ab->b_spa == 0)
1831                         continue;
1832 
1833                 /*
1834                  * It may take a long time to evict all the bufs requested.
1835                  * To avoid blocking all arc activity, periodically drop
1836                  * the arcs_mtx and give other threads a chance to run
1837                  * before reacquiring the lock.
1838                  *
1839                  * If we are looking for a buffer to recycle, we are in
1840                  * the hot code path, so don't sleep.
1841                  */
1842                 if (!recycle && count++ > arc_evict_iterations) {
1843                         list_insert_after(list, ab, &marker);
1844                         mutex_exit(&evicted_state->arcs_mtx);
1845                         mutex_exit(&state->arcs_mtx);
1846                         kpreempt(KPREEMPT_SYNC);
1847                         mutex_enter(&state->arcs_mtx);
1848                         mutex_enter(&evicted_state->arcs_mtx);
1849                         ab_prev = list_prev(list, &marker);
1850                         list_remove(list, &marker);
1851                         count = 0;
1852                         continue;
1853                 }
1854 
1855                 hash_lock = HDR_LOCK(ab);
1856                 have_lock = MUTEX_HELD(hash_lock);
1857                 if (have_lock || mutex_tryenter(hash_lock)) {
1858                         ASSERT0(refcount_count(&ab->b_refcnt));
1859                         ASSERT(ab->b_datacnt > 0);
1860                         while (ab->b_buf) {
1861                                 arc_buf_t *buf = ab->b_buf;
1862                                 if (!mutex_tryenter(&buf->b_evict_lock)) {
1863                                         missed += 1;
1864                                         break;
1865                                 }
1866                                 if (buf->b_data) {
1867                                         bytes_evicted += ab->b_size;
1868                                         if (recycle && ab->b_type == type &&
1869                                             ab->b_size == bytes &&
1870                                             !HDR_L2_WRITING(ab)) {
1871                                                 stolen = buf->b_data;
1872                                                 recycle = FALSE;
1873                                         }
1874                                 }
1875                                 if (buf->b_efunc) {
1876                                         mutex_enter(&arc_eviction_mtx);
1877                                         arc_buf_destroy(buf,
1878                                             buf->b_data == stolen, FALSE);
1879                                         ab->b_buf = buf->b_next;
1880                                         buf->b_hdr = &arc_eviction_hdr;
1881                                         buf->b_next = arc_eviction_list;
1882                                         arc_eviction_list = buf;
1883                                         mutex_exit(&arc_eviction_mtx);
1884                                         mutex_exit(&buf->b_evict_lock);
1885                                 } else {
1886                                         mutex_exit(&buf->b_evict_lock);
1887                                         arc_buf_destroy(buf,
1888                                             buf->b_data == stolen, TRUE);
1889                                 }
1890                         }
1891 
1892                         if (ab->b_l2hdr) {
1893                                 ARCSTAT_INCR(arcstat_evict_l2_cached,
1894                                     ab->b_size);
1895                         } else {
1896                                 if (l2arc_write_eligible(ab->b_spa, ab)) {
1897                                         ARCSTAT_INCR(arcstat_evict_l2_eligible,
1898                                             ab->b_size);
1899                                 } else {
1900                                         ARCSTAT_INCR(
1901                                             arcstat_evict_l2_ineligible,
1902                                             ab->b_size);
1903                                 }
1904                         }
1905 
1906                         if (ab->b_datacnt == 0) {
1907                                 arc_change_state(evicted_state, ab, hash_lock);
1908                                 ASSERT(HDR_IN_HASH_TABLE(ab));
1909                                 ab->b_flags |= ARC_IN_HASH_TABLE;
1910                                 ab->b_flags &= ~ARC_BUF_AVAILABLE;
1911                                 DTRACE_PROBE1(arc__evict, arc_buf_hdr_t *, ab);
1912                         }
1913                         if (!have_lock)
1914                                 mutex_exit(hash_lock);
1915                         if (bytes >= 0 && bytes_evicted >= bytes)
1916                                 break;
1917                 } else {
1918                         missed += 1;
1919                 }
1920         }
1921 
1922         mutex_exit(&evicted_state->arcs_mtx);
1923         mutex_exit(&state->arcs_mtx);
1924 
1925         if (bytes_evicted < bytes)
1926                 dprintf("only evicted %lld bytes from %x",
1927                     (longlong_t)bytes_evicted, state);
1928 
1929         if (skipped)
1930                 ARCSTAT_INCR(arcstat_evict_skip, skipped);
1931 
1932         if (missed)
1933                 ARCSTAT_INCR(arcstat_mutex_miss, missed);
1934 
1935         /*
1936          * Note: we have just evicted some data into the ghost state,
1937          * potentially putting the ghost size over the desired size.  Rather
1938          * that evicting from the ghost list in this hot code path, leave
1939          * this chore to the arc_reclaim_thread().
1940          */
1941 
1942         return (stolen);
1943 }
1944 
1945 /*
1946  * Remove buffers from list until we've removed the specified number of
1947  * bytes.  Destroy the buffers that are removed.
1948  */
1949 static void
1950 arc_evict_ghost(arc_state_t *state, uint64_t spa, int64_t bytes)
1951 {
1952         arc_buf_hdr_t *ab, *ab_prev;
1953         arc_buf_hdr_t marker = { 0 };
1954         list_t *list = &state->arcs_list[ARC_BUFC_DATA];
1955         kmutex_t *hash_lock;
1956         uint64_t bytes_deleted = 0;
1957         uint64_t bufs_skipped = 0;
1958         int count = 0;
1959 
1960         ASSERT(GHOST_STATE(state));
1961 top:
1962         mutex_enter(&state->arcs_mtx);
1963         for (ab = list_tail(list); ab; ab = ab_prev) {
1964                 ab_prev = list_prev(list, ab);
1965                 if (ab->b_type > ARC_BUFC_NUMTYPES)
1966                         panic("invalid ab=%p", (void *)ab);
1967                 if (spa && ab->b_spa != spa)
1968                         continue;
1969 
1970                 /* ignore markers */
1971                 if (ab->b_spa == 0)
1972                         continue;
1973 
1974                 hash_lock = HDR_LOCK(ab);
1975                 /* caller may be trying to modify this buffer, skip it */
1976                 if (MUTEX_HELD(hash_lock))
1977                         continue;
1978 
1979                 /*
1980                  * It may take a long time to evict all the bufs requested.
1981                  * To avoid blocking all arc activity, periodically drop
1982                  * the arcs_mtx and give other threads a chance to run
1983                  * before reacquiring the lock.
1984                  */
1985                 if (count++ > arc_evict_iterations) {
1986                         list_insert_after(list, ab, &marker);
1987                         mutex_exit(&state->arcs_mtx);
1988                         kpreempt(KPREEMPT_SYNC);
1989                         mutex_enter(&state->arcs_mtx);
1990                         ab_prev = list_prev(list, &marker);
1991                         list_remove(list, &marker);
1992                         count = 0;
1993                         continue;
1994                 }
1995                 if (mutex_tryenter(hash_lock)) {
1996                         ASSERT(!HDR_IO_IN_PROGRESS(ab));
1997                         ASSERT(ab->b_buf == NULL);
1998                         ARCSTAT_BUMP(arcstat_deleted);
1999                         bytes_deleted += ab->b_size;
2000 
2001                         if (ab->b_l2hdr != NULL) {
2002                                 /*
2003                                  * This buffer is cached on the 2nd Level ARC;
2004                                  * don't destroy the header.
2005                                  */
2006                                 arc_change_state(arc_l2c_only, ab, hash_lock);
2007                                 mutex_exit(hash_lock);
2008                         } else {
2009                                 arc_change_state(arc_anon, ab, hash_lock);
2010                                 mutex_exit(hash_lock);
2011                                 arc_hdr_destroy(ab);
2012                         }
2013 
2014                         DTRACE_PROBE1(arc__delete, arc_buf_hdr_t *, ab);
2015                         if (bytes >= 0 && bytes_deleted >= bytes)
2016                                 break;
2017                 } else if (bytes < 0) {
2018                         /*
2019                          * Insert a list marker and then wait for the
2020                          * hash lock to become available. Once its
2021                          * available, restart from where we left off.
2022                          */
2023                         list_insert_after(list, ab, &marker);
2024                         mutex_exit(&state->arcs_mtx);
2025                         mutex_enter(hash_lock);
2026                         mutex_exit(hash_lock);
2027                         mutex_enter(&state->arcs_mtx);
2028                         ab_prev = list_prev(list, &marker);
2029                         list_remove(list, &marker);
2030                 } else {
2031                         bufs_skipped += 1;
2032                 }
2033 
2034         }
2035         mutex_exit(&state->arcs_mtx);
2036 
2037         if (list == &state->arcs_list[ARC_BUFC_DATA] &&
2038             (bytes < 0 || bytes_deleted < bytes)) {
2039                 list = &state->arcs_list[ARC_BUFC_METADATA];
2040                 goto top;
2041         }
2042 
2043         if (bufs_skipped) {
2044                 ARCSTAT_INCR(arcstat_mutex_miss, bufs_skipped);
2045                 ASSERT(bytes >= 0);
2046         }
2047 
2048         if (bytes_deleted < bytes)
2049                 dprintf("only deleted %lld bytes from %p",
2050                     (longlong_t)bytes_deleted, state);
2051 }
2052 
2053 static void
2054 arc_adjust(void)
2055 {
2056         int64_t adjustment, delta;
2057 
2058         /*
2059          * Adjust MRU size
2060          */
2061 
2062         adjustment = MIN((int64_t)(arc_size - arc_c),
2063             (int64_t)(arc_anon->arcs_size + arc_mru->arcs_size + arc_meta_used -
2064             arc_p));
2065 
2066         if (adjustment > 0 && arc_mru->arcs_lsize[ARC_BUFC_DATA] > 0) {
2067                 delta = MIN(arc_mru->arcs_lsize[ARC_BUFC_DATA], adjustment);
2068                 (void) arc_evict(arc_mru, NULL, delta, FALSE, ARC_BUFC_DATA);
2069                 adjustment -= delta;
2070         }
2071 
2072         if (adjustment > 0 && arc_mru->arcs_lsize[ARC_BUFC_METADATA] > 0) {
2073                 delta = MIN(arc_mru->arcs_lsize[ARC_BUFC_METADATA], adjustment);
2074                 (void) arc_evict(arc_mru, NULL, delta, FALSE,
2075                     ARC_BUFC_METADATA);
2076         }
2077 
2078         /*
2079          * Adjust MFU size
2080          */
2081 
2082         adjustment = arc_size - arc_c;
2083 
2084         if (adjustment > 0 && arc_mfu->arcs_lsize[ARC_BUFC_DATA] > 0) {
2085                 delta = MIN(adjustment, arc_mfu->arcs_lsize[ARC_BUFC_DATA]);
2086                 (void) arc_evict(arc_mfu, NULL, delta, FALSE, ARC_BUFC_DATA);
2087                 adjustment -= delta;
2088         }
2089 
2090         if (adjustment > 0 && arc_mfu->arcs_lsize[ARC_BUFC_METADATA] > 0) {
2091                 int64_t delta = MIN(adjustment,
2092                     arc_mfu->arcs_lsize[ARC_BUFC_METADATA]);
2093                 (void) arc_evict(arc_mfu, NULL, delta, FALSE,
2094                     ARC_BUFC_METADATA);
2095         }
2096 
2097         /*
2098          * Adjust ghost lists
2099          */
2100 
2101         adjustment = arc_mru->arcs_size + arc_mru_ghost->arcs_size - arc_c;
2102 
2103         if (adjustment > 0 && arc_mru_ghost->arcs_size > 0) {
2104                 delta = MIN(arc_mru_ghost->arcs_size, adjustment);
2105                 arc_evict_ghost(arc_mru_ghost, NULL, delta);
2106         }
2107 
2108         adjustment =
2109             arc_mru_ghost->arcs_size + arc_mfu_ghost->arcs_size - arc_c;
2110 
2111         if (adjustment > 0 && arc_mfu_ghost->arcs_size > 0) {
2112                 delta = MIN(arc_mfu_ghost->arcs_size, adjustment);
2113                 arc_evict_ghost(arc_mfu_ghost, NULL, delta);
2114         }
2115 }
2116 
2117 static void
2118 arc_do_user_evicts(void)
2119 {
2120         mutex_enter(&arc_eviction_mtx);
2121         while (arc_eviction_list != NULL) {
2122                 arc_buf_t *buf = arc_eviction_list;
2123                 arc_eviction_list = buf->b_next;
2124                 mutex_enter(&buf->b_evict_lock);
2125                 buf->b_hdr = NULL;
2126                 mutex_exit(&buf->b_evict_lock);
2127                 mutex_exit(&arc_eviction_mtx);
2128 
2129                 if (buf->b_efunc != NULL)
2130                         VERIFY0(buf->b_efunc(buf->b_private));
2131 
2132                 buf->b_efunc = NULL;
2133                 buf->b_private = NULL;
2134                 kmem_cache_free(buf_cache, buf);
2135                 mutex_enter(&arc_eviction_mtx);
2136         }
2137         mutex_exit(&arc_eviction_mtx);
2138 }
2139 
2140 /*
2141  * Flush all *evictable* data from the cache for the given spa.
2142  * NOTE: this will not touch "active" (i.e. referenced) data.
2143  */
2144 void
2145 arc_flush(spa_t *spa)
2146 {
2147         uint64_t guid = 0;
2148 
2149         if (spa)
2150                 guid = spa_load_guid(spa);
2151 
2152         while (list_head(&arc_mru->arcs_list[ARC_BUFC_DATA])) {
2153                 (void) arc_evict(arc_mru, guid, -1, FALSE, ARC_BUFC_DATA);
2154                 if (spa)
2155                         break;
2156         }
2157         while (list_head(&arc_mru->arcs_list[ARC_BUFC_METADATA])) {
2158                 (void) arc_evict(arc_mru, guid, -1, FALSE, ARC_BUFC_METADATA);
2159                 if (spa)
2160                         break;
2161         }
2162         while (list_head(&arc_mfu->arcs_list[ARC_BUFC_DATA])) {
2163                 (void) arc_evict(arc_mfu, guid, -1, FALSE, ARC_BUFC_DATA);
2164                 if (spa)
2165                         break;
2166         }
2167         while (list_head(&arc_mfu->arcs_list[ARC_BUFC_METADATA])) {
2168                 (void) arc_evict(arc_mfu, guid, -1, FALSE, ARC_BUFC_METADATA);
2169                 if (spa)
2170                         break;
2171         }
2172 
2173         arc_evict_ghost(arc_mru_ghost, guid, -1);
2174         arc_evict_ghost(arc_mfu_ghost, guid, -1);
2175 
2176         mutex_enter(&arc_reclaim_thr_lock);
2177         arc_do_user_evicts();
2178         mutex_exit(&arc_reclaim_thr_lock);
2179         ASSERT(spa || arc_eviction_list == NULL);
2180 }
2181 
2182 void
2183 arc_shrink(void)
2184 {
2185         if (arc_c > arc_c_min) {
2186                 uint64_t to_free;
2187 
2188 #ifdef _KERNEL
2189                 to_free = MAX(arc_c >> arc_shrink_shift, ptob(needfree));
2190 #else
2191                 to_free = arc_c >> arc_shrink_shift;
2192 #endif
2193                 if (arc_c > arc_c_min + to_free)
2194                         atomic_add_64(&arc_c, -to_free);
2195                 else
2196                         arc_c = arc_c_min;
2197 
2198                 atomic_add_64(&arc_p, -(arc_p >> arc_shrink_shift));
2199                 if (arc_c > arc_size)
2200                         arc_c = MAX(arc_size, arc_c_min);
2201                 if (arc_p > arc_c)
2202                         arc_p = (arc_c >> 1);
2203                 ASSERT(arc_c >= arc_c_min);
2204                 ASSERT((int64_t)arc_p >= 0);
2205         }
2206 
2207         if (arc_size > arc_c)
2208                 arc_adjust();
2209 }
2210 
2211 /*
2212  * Determine if the system is under memory pressure and is asking
2213  * to reclaim memory. A return value of 1 indicates that the system
2214  * is under memory pressure and that the arc should adjust accordingly.
2215  */
2216 static int
2217 arc_reclaim_needed(void)
2218 {
2219         uint64_t extra;
2220 
2221 #ifdef _KERNEL
2222 
2223         if (needfree)
2224                 return (1);
2225 
2226         /*
2227          * take 'desfree' extra pages, so we reclaim sooner, rather than later
2228          */
2229         extra = desfree;
2230 
2231         /*
2232          * check that we're out of range of the pageout scanner.  It starts to
2233          * schedule paging if freemem is less than lotsfree and needfree.
2234          * lotsfree is the high-water mark for pageout, and needfree is the
2235          * number of needed free pages.  We add extra pages here to make sure
2236          * the scanner doesn't start up while we're freeing memory.
2237          */
2238         if (freemem < lotsfree + needfree + extra)
2239                 return (1);
2240 
2241         /*
2242          * check to make sure that swapfs has enough space so that anon
2243          * reservations can still succeed. anon_resvmem() checks that the
2244          * availrmem is greater than swapfs_minfree, and the number of reserved
2245          * swap pages.  We also add a bit of extra here just to prevent
2246          * circumstances from getting really dire.
2247          */
2248         if (availrmem < swapfs_minfree + swapfs_reserve + extra)
2249                 return (1);
2250 
2251         /*
2252          * Check that we have enough availrmem that memory locking (e.g., via
2253          * mlock(3C) or memcntl(2)) can still succeed.  (pages_pp_maximum
2254          * stores the number of pages that cannot be locked; when availrmem
2255          * drops below pages_pp_maximum, page locking mechanisms such as
2256          * page_pp_lock() will fail.)
2257          */
2258         if (availrmem <= pages_pp_maximum)
2259                 return (1);
2260 
2261 #if defined(__i386)
2262         /*
2263          * If we're on an i386 platform, it's possible that we'll exhaust the
2264          * kernel heap space before we ever run out of available physical
2265          * memory.  Most checks of the size of the heap_area compare against
2266          * tune.t_minarmem, which is the minimum available real memory that we
2267          * can have in the system.  However, this is generally fixed at 25 pages
2268          * which is so low that it's useless.  In this comparison, we seek to
2269          * calculate the total heap-size, and reclaim if more than 3/4ths of the
2270          * heap is allocated.  (Or, in the calculation, if less than 1/4th is
2271          * free)
2272          */
2273         if (vmem_size(heap_arena, VMEM_FREE) <
2274             (vmem_size(heap_arena, VMEM_FREE | VMEM_ALLOC) >> 2))
2275                 return (1);
2276 #endif
2277 
2278         /*
2279          * If zio data pages are being allocated out of a separate heap segment,
2280          * then enforce that the size of available vmem for this arena remains
2281          * above about 1/16th free.
2282          *
2283          * Note: The 1/16th arena free requirement was put in place
2284          * to aggressively evict memory from the arc in order to avoid
2285          * memory fragmentation issues.
2286          */
2287         if (zio_arena != NULL &&
2288             vmem_size(zio_arena, VMEM_FREE) <
2289             (vmem_size(zio_arena, VMEM_ALLOC) >> 4))
2290                 return (1);
2291 #else
2292         if (spa_get_random(100) == 0)
2293                 return (1);
2294 #endif
2295         return (0);
2296 }
2297 
2298 static void
2299 arc_kmem_reap_now(arc_reclaim_strategy_t strat)
2300 {
2301         size_t                  i;
2302         kmem_cache_t            *prev_cache = NULL;
2303         kmem_cache_t            *prev_data_cache = NULL;
2304         extern kmem_cache_t     *zio_buf_cache[];
2305         extern kmem_cache_t     *zio_data_buf_cache[];
2306         extern kmem_cache_t     *range_seg_cache;
2307 
2308 #ifdef _KERNEL
2309         if (arc_meta_used >= arc_meta_limit) {
2310                 /*
2311                  * We are exceeding our meta-data cache limit.
2312                  * Purge some DNLC entries to release holds on meta-data.
2313                  */
2314                 dnlc_reduce_cache((void *)(uintptr_t)arc_reduce_dnlc_percent);
2315         }
2316 #if defined(__i386)
2317         /*
2318          * Reclaim unused memory from all kmem caches.
2319          */
2320         kmem_reap();
2321 #endif
2322 #endif
2323 
2324         /*
2325          * An aggressive reclamation will shrink the cache size as well as
2326          * reap free buffers from the arc kmem caches.
2327          */
2328         if (strat == ARC_RECLAIM_AGGR)
2329                 arc_shrink();
2330 
2331         for (i = 0; i < SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT; i++) {
2332                 if (zio_buf_cache[i] != prev_cache) {
2333                         prev_cache = zio_buf_cache[i];
2334                         kmem_cache_reap_now(zio_buf_cache[i]);
2335                 }
2336                 if (zio_data_buf_cache[i] != prev_data_cache) {
2337                         prev_data_cache = zio_data_buf_cache[i];
2338                         kmem_cache_reap_now(zio_data_buf_cache[i]);
2339                 }
2340         }
2341         kmem_cache_reap_now(buf_cache);
2342         kmem_cache_reap_now(hdr_cache);
2343         kmem_cache_reap_now(range_seg_cache);
2344 
2345         /*
2346          * Ask the vmem areana to reclaim unused memory from its
2347          * quantum caches.
2348          */
2349         if (zio_arena != NULL && strat == ARC_RECLAIM_AGGR)
2350                 vmem_qcache_reap(zio_arena);
2351 }
2352 
2353 static void
2354 arc_reclaim_thread(void)
2355 {
2356         clock_t                 growtime = 0;
2357         arc_reclaim_strategy_t  last_reclaim = ARC_RECLAIM_CONS;
2358         callb_cpr_t             cpr;
2359 
2360         CALLB_CPR_INIT(&cpr, &arc_reclaim_thr_lock, callb_generic_cpr, FTAG);
2361 
2362         mutex_enter(&arc_reclaim_thr_lock);
2363         while (arc_thread_exit == 0) {
2364                 if (arc_reclaim_needed()) {
2365 
2366                         if (arc_no_grow) {
2367                                 if (last_reclaim == ARC_RECLAIM_CONS) {
2368                                         last_reclaim = ARC_RECLAIM_AGGR;
2369                                 } else {
2370                                         last_reclaim = ARC_RECLAIM_CONS;
2371                                 }
2372                         } else {
2373                                 arc_no_grow = TRUE;
2374                                 last_reclaim = ARC_RECLAIM_AGGR;
2375                                 membar_producer();
2376                         }
2377 
2378                         /* reset the growth delay for every reclaim */
2379                         growtime = ddi_get_lbolt() + (arc_grow_retry * hz);
2380 
2381                         arc_kmem_reap_now(last_reclaim);
2382                         arc_warm = B_TRUE;
2383 
2384                 } else if (arc_no_grow && ddi_get_lbolt() >= growtime) {
2385                         arc_no_grow = FALSE;
2386                 }
2387 
2388                 arc_adjust();
2389 
2390                 if (arc_eviction_list != NULL)
2391                         arc_do_user_evicts();
2392 
2393                 /* block until needed, or one second, whichever is shorter */
2394                 CALLB_CPR_SAFE_BEGIN(&cpr);
2395                 (void) cv_timedwait(&arc_reclaim_thr_cv,
2396                     &arc_reclaim_thr_lock, (ddi_get_lbolt() + hz));
2397                 CALLB_CPR_SAFE_END(&cpr, &arc_reclaim_thr_lock);
2398         }
2399 
2400         arc_thread_exit = 0;
2401         cv_broadcast(&arc_reclaim_thr_cv);
2402         CALLB_CPR_EXIT(&cpr);               /* drops arc_reclaim_thr_lock */
2403         thread_exit();
2404 }
2405 
2406 /*
2407  * Adapt arc info given the number of bytes we are trying to add and
2408  * the state that we are comming from.  This function is only called
2409  * when we are adding new content to the cache.
2410  */
2411 static void
2412 arc_adapt(int bytes, arc_state_t *state)
2413 {
2414         int mult;
2415         uint64_t arc_p_min = (arc_c >> arc_p_min_shift);
2416 
2417         if (state == arc_l2c_only)
2418                 return;
2419 
2420         ASSERT(bytes > 0);
2421         /*
2422          * Adapt the target size of the MRU list:
2423          *      - if we just hit in the MRU ghost list, then increase
2424          *        the target size of the MRU list.
2425          *      - if we just hit in the MFU ghost list, then increase
2426          *        the target size of the MFU list by decreasing the
2427          *        target size of the MRU list.
2428          */
2429         if (state == arc_mru_ghost) {
2430                 mult = ((arc_mru_ghost->arcs_size >= arc_mfu_ghost->arcs_size) ?
2431                     1 : (arc_mfu_ghost->arcs_size/arc_mru_ghost->arcs_size));
2432                 mult = MIN(mult, 10); /* avoid wild arc_p adjustment */
2433 
2434                 arc_p = MIN(arc_c - arc_p_min, arc_p + bytes * mult);
2435         } else if (state == arc_mfu_ghost) {
2436                 uint64_t delta;
2437 
2438                 mult = ((arc_mfu_ghost->arcs_size >= arc_mru_ghost->arcs_size) ?
2439                     1 : (arc_mru_ghost->arcs_size/arc_mfu_ghost->arcs_size));
2440                 mult = MIN(mult, 10);
2441 
2442                 delta = MIN(bytes * mult, arc_p);
2443                 arc_p = MAX(arc_p_min, arc_p - delta);
2444         }
2445         ASSERT((int64_t)arc_p >= 0);
2446 
2447         if (arc_reclaim_needed()) {
2448                 cv_signal(&arc_reclaim_thr_cv);
2449                 return;
2450         }
2451 
2452         if (arc_no_grow)
2453                 return;
2454 
2455         if (arc_c >= arc_c_max)
2456                 return;
2457 
2458         /*
2459          * If we're within (2 * maxblocksize) bytes of the target
2460          * cache size, increment the target cache size
2461          */
2462         if (arc_size > arc_c - (2ULL << SPA_MAXBLOCKSHIFT)) {
2463                 atomic_add_64(&arc_c, (int64_t)bytes);
2464                 if (arc_c > arc_c_max)
2465                         arc_c = arc_c_max;
2466                 else if (state == arc_anon)
2467                         atomic_add_64(&arc_p, (int64_t)bytes);
2468                 if (arc_p > arc_c)
2469                         arc_p = arc_c;
2470         }
2471         ASSERT((int64_t)arc_p >= 0);
2472 }
2473 
2474 /*
2475  * Check if the cache has reached its limits and eviction is required
2476  * prior to insert.
2477  */
2478 static int
2479 arc_evict_needed(arc_buf_contents_t type)
2480 {
2481         if (type == ARC_BUFC_METADATA && arc_meta_used >= arc_meta_limit)
2482                 return (1);
2483 
2484         if (arc_reclaim_needed())
2485                 return (1);
2486 
2487         return (arc_size > arc_c);
2488 }
2489 
2490 /*
2491  * The buffer, supplied as the first argument, needs a data block.
2492  * So, if we are at cache max, determine which cache should be victimized.
2493  * We have the following cases:
2494  *
2495  * 1. Insert for MRU, p > sizeof(arc_anon + arc_mru) ->
2496  * In this situation if we're out of space, but the resident size of the MFU is
2497  * under the limit, victimize the MFU cache to satisfy this insertion request.
2498  *
2499  * 2. Insert for MRU, p <= sizeof(arc_anon + arc_mru) ->
2500  * Here, we've used up all of the available space for the MRU, so we need to
2501  * evict from our own cache instead.  Evict from the set of resident MRU
2502  * entries.
2503  *
2504  * 3. Insert for MFU (c - p) > sizeof(arc_mfu) ->
2505  * c minus p represents the MFU space in the cache, since p is the size of the
2506  * cache that is dedicated to the MRU.  In this situation there's still space on
2507  * the MFU side, so the MRU side needs to be victimized.
2508  *
2509  * 4. Insert for MFU (c - p) < sizeof(arc_mfu) ->
2510  * MFU's resident set is consuming more space than it has been allotted.  In
2511  * this situation, we must victimize our own cache, the MFU, for this insertion.
2512  */
2513 static void
2514 arc_get_data_buf(arc_buf_t *buf)
2515 {
2516         arc_state_t             *state = buf->b_hdr->b_state;
2517         uint64_t                size = buf->b_hdr->b_size;
2518         arc_buf_contents_t      type = buf->b_hdr->b_type;
2519 
2520         arc_adapt(size, state);
2521 
2522         /*
2523          * We have not yet reached cache maximum size,
2524          * just allocate a new buffer.
2525          */
2526         if (!arc_evict_needed(type)) {
2527                 if (type == ARC_BUFC_METADATA) {
2528                         buf->b_data = zio_buf_alloc(size);
2529                         arc_space_consume(size, ARC_SPACE_DATA);
2530                 } else {
2531                         ASSERT(type == ARC_BUFC_DATA);
2532                         buf->b_data = zio_data_buf_alloc(size);
2533                         ARCSTAT_INCR(arcstat_data_size, size);
2534                         atomic_add_64(&arc_size, size);
2535                 }
2536                 goto out;
2537         }
2538 
2539         /*
2540          * If we are prefetching from the mfu ghost list, this buffer
2541          * will end up on the mru list; so steal space from there.
2542          */
2543         if (state == arc_mfu_ghost)
2544                 state = buf->b_hdr->b_flags & ARC_PREFETCH ? arc_mru : arc_mfu;
2545         else if (state == arc_mru_ghost)
2546                 state = arc_mru;
2547 
2548         if (state == arc_mru || state == arc_anon) {
2549                 uint64_t mru_used = arc_anon->arcs_size + arc_mru->arcs_size;
2550                 state = (arc_mfu->arcs_lsize[type] >= size &&
2551                     arc_p > mru_used) ? arc_mfu : arc_mru;
2552         } else {
2553                 /* MFU cases */
2554                 uint64_t mfu_space = arc_c - arc_p;
2555                 state =  (arc_mru->arcs_lsize[type] >= size &&
2556                     mfu_space > arc_mfu->arcs_size) ? arc_mru : arc_mfu;
2557         }
2558         if ((buf->b_data = arc_evict(state, NULL, size, TRUE, type)) == NULL) {
2559                 if (type == ARC_BUFC_METADATA) {
2560                         buf->b_data = zio_buf_alloc(size);
2561                         arc_space_consume(size, ARC_SPACE_DATA);
2562                 } else {
2563                         ASSERT(type == ARC_BUFC_DATA);
2564                         buf->b_data = zio_data_buf_alloc(size);
2565                         ARCSTAT_INCR(arcstat_data_size, size);
2566                         atomic_add_64(&arc_size, size);
2567                 }
2568                 ARCSTAT_BUMP(arcstat_recycle_miss);
2569         }
2570         ASSERT(buf->b_data != NULL);
2571 out:
2572         /*
2573          * Update the state size.  Note that ghost states have a
2574          * "ghost size" and so don't need to be updated.
2575          */
2576         if (!GHOST_STATE(buf->b_hdr->b_state)) {
2577                 arc_buf_hdr_t *hdr = buf->b_hdr;
2578 
2579                 atomic_add_64(&hdr->b_state->arcs_size, size);
2580                 if (list_link_active(&hdr->b_arc_node)) {
2581                         ASSERT(refcount_is_zero(&hdr->b_refcnt));
2582                         atomic_add_64(&hdr->b_state->arcs_lsize[type], size);
2583                 }
2584                 /*
2585                  * If we are growing the cache, and we are adding anonymous
2586                  * data, and we have outgrown arc_p, update arc_p
2587                  */
2588                 if (arc_size < arc_c && hdr->b_state == arc_anon &&
2589                     arc_anon->arcs_size + arc_mru->arcs_size > arc_p)
2590                         arc_p = MIN(arc_c, arc_p + size);
2591         }
2592 }
2593 
2594 /*
2595  * This routine is called whenever a buffer is accessed.
2596  * NOTE: the hash lock is dropped in this function.
2597  */
2598 static void
2599 arc_access(arc_buf_hdr_t *buf, kmutex_t *hash_lock)
2600 {
2601         clock_t now;
2602 
2603         ASSERT(MUTEX_HELD(hash_lock));
2604 
2605         if (buf->b_state == arc_anon) {
2606                 /*
2607                  * This buffer is not in the cache, and does not
2608                  * appear in our "ghost" list.  Add the new buffer
2609                  * to the MRU state.
2610                  */
2611 
2612                 ASSERT(buf->b_arc_access == 0);
2613                 buf->b_arc_access = ddi_get_lbolt();
2614                 DTRACE_PROBE1(new_state__mru, arc_buf_hdr_t *, buf);
2615                 arc_change_state(arc_mru, buf, hash_lock);
2616 
2617         } else if (buf->b_state == arc_mru) {
2618                 now = ddi_get_lbolt();
2619 
2620                 /*
2621                  * If this buffer is here because of a prefetch, then either:
2622                  * - clear the flag if this is a "referencing" read
2623                  *   (any subsequent access will bump this into the MFU state).
2624                  * or
2625                  * - move the buffer to the head of the list if this is
2626                  *   another prefetch (to make it less likely to be evicted).
2627                  */
2628                 if ((buf->b_flags & ARC_PREFETCH) != 0) {
2629                         if (refcount_count(&buf->b_refcnt) == 0) {
2630                                 ASSERT(list_link_active(&buf->b_arc_node));
2631                         } else {
2632                                 buf->b_flags &= ~ARC_PREFETCH;
2633                                 ARCSTAT_BUMP(arcstat_mru_hits);
2634                         }
2635                         buf->b_arc_access = now;
2636                         return;
2637                 }
2638 
2639                 /*
2640                  * This buffer has been "accessed" only once so far,
2641                  * but it is still in the cache. Move it to the MFU
2642                  * state.
2643                  */
2644                 if (now > buf->b_arc_access + ARC_MINTIME) {
2645                         /*
2646                          * More than 125ms have passed since we
2647                          * instantiated this buffer.  Move it to the
2648                          * most frequently used state.
2649                          */
2650                         buf->b_arc_access = now;
2651                         DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, buf);
2652                         arc_change_state(arc_mfu, buf, hash_lock);
2653                 }
2654                 ARCSTAT_BUMP(arcstat_mru_hits);
2655         } else if (buf->b_state == arc_mru_ghost) {
2656                 arc_state_t     *new_state;
2657                 /*
2658                  * This buffer has been "accessed" recently, but
2659                  * was evicted from the cache.  Move it to the
2660                  * MFU state.
2661                  */
2662 
2663                 if (buf->b_flags & ARC_PREFETCH) {
2664                         new_state = arc_mru;
2665                         if (refcount_count(&buf->b_refcnt) > 0)
2666                                 buf->b_flags &= ~ARC_PREFETCH;
2667                         DTRACE_PROBE1(new_state__mru, arc_buf_hdr_t *, buf);
2668                 } else {
2669                         new_state = arc_mfu;
2670                         DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, buf);
2671                 }
2672 
2673                 buf->b_arc_access = ddi_get_lbolt();
2674                 arc_change_state(new_state, buf, hash_lock);
2675 
2676                 ARCSTAT_BUMP(arcstat_mru_ghost_hits);
2677         } else if (buf->b_state == arc_mfu) {
2678                 /*
2679                  * This buffer has been accessed more than once and is
2680                  * still in the cache.  Keep it in the MFU state.
2681                  *
2682                  * NOTE: an add_reference() that occurred when we did
2683                  * the arc_read() will have kicked this off the list.
2684                  * If it was a prefetch, we will explicitly move it to
2685                  * the head of the list now.
2686                  */
2687                 if ((buf->b_flags & ARC_PREFETCH) != 0) {
2688                         ASSERT(refcount_count(&buf->b_refcnt) == 0);
2689                         ASSERT(list_link_active(&buf->b_arc_node));
2690                 }
2691                 ARCSTAT_BUMP(arcstat_mfu_hits);
2692                 buf->b_arc_access = ddi_get_lbolt();
2693         } else if (buf->b_state == arc_mfu_ghost) {
2694                 arc_state_t     *new_state = arc_mfu;
2695                 /*
2696                  * This buffer has been accessed more than once but has
2697                  * been evicted from the cache.  Move it back to the
2698                  * MFU state.
2699                  */
2700 
2701                 if (buf->b_flags & ARC_PREFETCH) {
2702                         /*
2703                          * This is a prefetch access...
2704                          * move this block back to the MRU state.
2705                          */
2706                         ASSERT0(refcount_count(&buf->b_refcnt));
2707                         new_state = arc_mru;
2708                 }
2709 
2710                 buf->b_arc_access = ddi_get_lbolt();
2711                 DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, buf);
2712                 arc_change_state(new_state, buf, hash_lock);
2713 
2714                 ARCSTAT_BUMP(arcstat_mfu_ghost_hits);
2715         } else if (buf->b_state == arc_l2c_only) {
2716                 /*
2717                  * This buffer is on the 2nd Level ARC.
2718                  */
2719 
2720                 buf->b_arc_access = ddi_get_lbolt();
2721                 DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, buf);
2722                 arc_change_state(arc_mfu, buf, hash_lock);
2723         } else {
2724                 ASSERT(!"invalid arc state");
2725         }
2726 }
2727 
2728 /* a generic arc_done_func_t which you can use */
2729 /* ARGSUSED */
2730 void
2731 arc_bcopy_func(zio_t *zio, arc_buf_t *buf, void *arg)
2732 {
2733         if (zio == NULL || zio->io_error == 0)
2734                 bcopy(buf->b_data, arg, buf->b_hdr->b_size);
2735         VERIFY(arc_buf_remove_ref(buf, arg));
2736 }
2737 
2738 /* a generic arc_done_func_t */
2739 void
2740 arc_getbuf_func(zio_t *zio, arc_buf_t *buf, void *arg)
2741 {
2742         arc_buf_t **bufp = arg;
2743         if (zio && zio->io_error) {
2744                 VERIFY(arc_buf_remove_ref(buf, arg));
2745                 *bufp = NULL;
2746         } else {
2747                 *bufp = buf;
2748                 ASSERT(buf->b_data);
2749         }
2750 }
2751 
2752 static void
2753 arc_read_done(zio_t *zio)
2754 {
2755         arc_buf_hdr_t   *hdr;
2756         arc_buf_t       *buf;
2757         arc_buf_t       *abuf;  /* buffer we're assigning to callback */
2758         kmutex_t        *hash_lock = NULL;
2759         arc_callback_t  *callback_list, *acb;
2760         int             freeable = FALSE;
2761 
2762         buf = zio->io_private;
2763         hdr = buf->b_hdr;
2764 
2765         /*
2766          * The hdr was inserted into hash-table and removed from lists
2767          * prior to starting I/O.  We should find this header, since
2768          * it's in the hash table, and it should be legit since it's
2769          * not possible to evict it during the I/O.  The only possible
2770          * reason for it not to be found is if we were freed during the
2771          * read.
2772          */
2773         if (HDR_IN_HASH_TABLE(hdr)) {
2774                 ASSERT3U(hdr->b_birth, ==, BP_PHYSICAL_BIRTH(zio->io_bp));
2775                 ASSERT3U(hdr->b_dva.dva_word[0], ==,
2776                     BP_IDENTITY(zio->io_bp)->dva_word[0]);
2777                 ASSERT3U(hdr->b_dva.dva_word[1], ==,
2778                     BP_IDENTITY(zio->io_bp)->dva_word[1]);
2779 
2780                 arc_buf_hdr_t *found = buf_hash_find(hdr->b_spa, zio->io_bp,
2781                     &hash_lock);
2782 
2783                 ASSERT((found == NULL && HDR_FREED_IN_READ(hdr) &&
2784                     hash_lock == NULL) ||
2785                     (found == hdr &&
2786                     DVA_EQUAL(&hdr->b_dva, BP_IDENTITY(zio->io_bp))) ||
2787                     (found == hdr && HDR_L2_READING(hdr)));
2788         }
2789 
2790         hdr->b_flags &= ~ARC_L2_EVICTED;
2791         if (l2arc_noprefetch && (hdr->b_flags & ARC_PREFETCH))
2792                 hdr->b_flags &= ~ARC_L2CACHE;
2793 
2794         /* byteswap if necessary */
2795         callback_list = hdr->b_acb;
2796         ASSERT(callback_list != NULL);
2797         if (BP_SHOULD_BYTESWAP(zio->io_bp) && zio->io_error == 0) {
2798                 dmu_object_byteswap_t bswap =
2799                     DMU_OT_BYTESWAP(BP_GET_TYPE(zio->io_bp));
2800                 arc_byteswap_func_t *func = BP_GET_LEVEL(zio->io_bp) > 0 ?
2801                     byteswap_uint64_array :
2802                     dmu_ot_byteswap[bswap].ob_func;
2803                 func(buf->b_data, hdr->b_size);
2804         }
2805 
2806         arc_cksum_compute(buf, B_FALSE);
2807         arc_buf_watch(buf);
2808 
2809         if (hash_lock && zio->io_error == 0 && hdr->b_state == arc_anon) {
2810                 /*
2811                  * Only call arc_access on anonymous buffers.  This is because
2812                  * if we've issued an I/O for an evicted buffer, we've already
2813                  * called arc_access (to prevent any simultaneous readers from
2814                  * getting confused).
2815                  */
2816                 arc_access(hdr, hash_lock);
2817         }
2818 
2819         /* create copies of the data buffer for the callers */
2820         abuf = buf;
2821         for (acb = callback_list; acb; acb = acb->acb_next) {
2822                 if (acb->acb_done) {
2823                         if (abuf == NULL) {
2824                                 ARCSTAT_BUMP(arcstat_duplicate_reads);
2825                                 abuf = arc_buf_clone(buf);
2826                         }
2827                         acb->acb_buf = abuf;
2828                         abuf = NULL;
2829                 }
2830         }
2831         hdr->b_acb = NULL;
2832         hdr->b_flags &= ~ARC_IO_IN_PROGRESS;
2833         ASSERT(!HDR_BUF_AVAILABLE(hdr));
2834         if (abuf == buf) {
2835                 ASSERT(buf->b_efunc == NULL);
2836                 ASSERT(hdr->b_datacnt == 1);
2837                 hdr->b_flags |= ARC_BUF_AVAILABLE;
2838         }
2839 
2840         ASSERT(refcount_is_zero(&hdr->b_refcnt) || callback_list != NULL);
2841 
2842         if (zio->io_error != 0) {
2843                 hdr->b_flags |= ARC_IO_ERROR;
2844                 if (hdr->b_state != arc_anon)
2845                         arc_change_state(arc_anon, hdr, hash_lock);
2846                 if (HDR_IN_HASH_TABLE(hdr))
2847                         buf_hash_remove(hdr);
2848                 freeable = refcount_is_zero(&hdr->b_refcnt);
2849         }
2850 
2851         /*
2852          * Broadcast before we drop the hash_lock to avoid the possibility
2853          * that the hdr (and hence the cv) might be freed before we get to
2854          * the cv_broadcast().
2855          */
2856         cv_broadcast(&hdr->b_cv);
2857 
2858         if (hash_lock) {
2859                 mutex_exit(hash_lock);
2860         } else {
2861                 /*
2862                  * This block was freed while we waited for the read to
2863                  * complete.  It has been removed from the hash table and
2864                  * moved to the anonymous state (so that it won't show up
2865                  * in the cache).
2866                  */
2867                 ASSERT3P(hdr->b_state, ==, arc_anon);
2868                 freeable = refcount_is_zero(&hdr->b_refcnt);
2869         }
2870 
2871         /* execute each callback and free its structure */
2872         while ((acb = callback_list) != NULL) {
2873                 if (acb->acb_done)
2874                         acb->acb_done(zio, acb->acb_buf, acb->acb_private);
2875 
2876                 if (acb->acb_zio_dummy != NULL) {
2877                         acb->acb_zio_dummy->io_error = zio->io_error;
2878                         zio_nowait(acb->acb_zio_dummy);
2879                 }
2880 
2881                 callback_list = acb->acb_next;
2882                 kmem_free(acb, sizeof (arc_callback_t));
2883         }
2884 
2885         if (freeable)
2886                 arc_hdr_destroy(hdr);
2887 }
2888 
2889 /*
2890  * "Read" the block at the specified DVA (in bp) via the
2891  * cache.  If the block is found in the cache, invoke the provided
2892  * callback immediately and return.  Note that the `zio' parameter
2893  * in the callback will be NULL in this case, since no IO was
2894  * required.  If the block is not in the cache pass the read request
2895  * on to the spa with a substitute callback function, so that the
2896  * requested block will be added to the cache.
2897  *
2898  * If a read request arrives for a block that has a read in-progress,
2899  * either wait for the in-progress read to complete (and return the
2900  * results); or, if this is a read with a "done" func, add a record
2901  * to the read to invoke the "done" func when the read completes,
2902  * and return; or just return.
2903  *
2904  * arc_read_done() will invoke all the requested "done" functions
2905  * for readers of this block.
2906  */
2907 int
2908 arc_read(zio_t *pio, spa_t *spa, const blkptr_t *bp, arc_done_func_t *done,
2909     void *private, zio_priority_t priority, int zio_flags, uint32_t *arc_flags,
2910     const zbookmark_phys_t *zb)
2911 {
2912         arc_buf_hdr_t *hdr = NULL;
2913         arc_buf_t *buf = NULL;
2914         kmutex_t *hash_lock = NULL;
2915         zio_t *rzio;
2916         uint64_t guid = spa_load_guid(spa);
2917 
2918         ASSERT(!BP_IS_EMBEDDED(bp) ||
2919             BPE_GET_ETYPE(bp) == BP_EMBEDDED_TYPE_DATA);
2920 
2921 top:
2922         if (!BP_IS_EMBEDDED(bp)) {
2923                 /*
2924                  * Embedded BP's have no DVA and require no I/O to "read".
2925                  * Create an anonymous arc buf to back it.
2926                  */
2927                 hdr = buf_hash_find(guid, bp, &hash_lock);
2928         }
2929 
2930         if (hdr != NULL && hdr->b_datacnt > 0) {
2931 
2932                 *arc_flags |= ARC_CACHED;
2933 
2934                 if (HDR_IO_IN_PROGRESS(hdr)) {
2935 
2936                         if (*arc_flags & ARC_WAIT) {
2937                                 cv_wait(&hdr->b_cv, hash_lock);
2938                                 mutex_exit(hash_lock);
2939                                 goto top;
2940                         }
2941                         ASSERT(*arc_flags & ARC_NOWAIT);
2942 
2943                         if (done) {
2944                                 arc_callback_t  *acb = NULL;
2945 
2946                                 acb = kmem_zalloc(sizeof (arc_callback_t),
2947                                     KM_SLEEP);
2948                                 acb->acb_done = done;
2949                                 acb->acb_private = private;
2950                                 if (pio != NULL)
2951                                         acb->acb_zio_dummy = zio_null(pio,
2952                                             spa, NULL, NULL, NULL, zio_flags);
2953 
2954                                 ASSERT(acb->acb_done != NULL);
2955                                 acb->acb_next = hdr->b_acb;
2956                                 hdr->b_acb = acb;
2957                                 add_reference(hdr, hash_lock, private);
2958                                 mutex_exit(hash_lock);
2959                                 return (0);
2960                         }
2961                         mutex_exit(hash_lock);
2962                         return (0);
2963                 }
2964 
2965                 ASSERT(hdr->b_state == arc_mru || hdr->b_state == arc_mfu);
2966 
2967                 if (done) {
2968                         add_reference(hdr, hash_lock, private);
2969                         /*
2970                          * If this block is already in use, create a new
2971                          * copy of the data so that we will be guaranteed
2972                          * that arc_release() will always succeed.
2973                          */
2974                         buf = hdr->b_buf;
2975                         ASSERT(buf);
2976                         ASSERT(buf->b_data);
2977                         if (HDR_BUF_AVAILABLE(hdr)) {
2978                                 ASSERT(buf->b_efunc == NULL);
2979                                 hdr->b_flags &= ~ARC_BUF_AVAILABLE;
2980                         } else {
2981                                 buf = arc_buf_clone(buf);
2982                         }
2983 
2984                 } else if (*arc_flags & ARC_PREFETCH &&
2985                     refcount_count(&hdr->b_refcnt) == 0) {
2986                         hdr->b_flags |= ARC_PREFETCH;
2987                 }
2988                 DTRACE_PROBE1(arc__hit, arc_buf_hdr_t *, hdr);
2989                 arc_access(hdr, hash_lock);
2990                 if (*arc_flags & ARC_L2CACHE)
2991                         hdr->b_flags |= ARC_L2CACHE;
2992                 if (*arc_flags & ARC_L2COMPRESS)
2993                         hdr->b_flags |= ARC_L2COMPRESS;
2994                 mutex_exit(hash_lock);
2995                 ARCSTAT_BUMP(arcstat_hits);
2996                 ARCSTAT_CONDSTAT(!(hdr->b_flags & ARC_PREFETCH),
2997                     demand, prefetch, hdr->b_type != ARC_BUFC_METADATA,
2998                     data, metadata, hits);
2999 
3000                 if (done)
3001                         done(NULL, buf, private);
3002         } else {
3003                 uint64_t size = BP_GET_LSIZE(bp);
3004                 arc_callback_t *acb;
3005                 vdev_t *vd = NULL;
3006                 uint64_t addr = 0;
3007                 boolean_t devw = B_FALSE;
3008                 enum zio_compress b_compress = ZIO_COMPRESS_OFF;
3009                 uint64_t b_asize = 0;
3010 
3011                 if (hdr == NULL) {
3012                         /* this block is not in the cache */
3013                         arc_buf_hdr_t *exists = NULL;
3014                         arc_buf_contents_t type = BP_GET_BUFC_TYPE(bp);
3015                         buf = arc_buf_alloc(spa, size, private, type);
3016                         hdr = buf->b_hdr;
3017                         if (!BP_IS_EMBEDDED(bp)) {
3018                                 hdr->b_dva = *BP_IDENTITY(bp);
3019                                 hdr->b_birth = BP_PHYSICAL_BIRTH(bp);
3020                                 hdr->b_cksum0 = bp->blk_cksum.zc_word[0];
3021                                 exists = buf_hash_insert(hdr, &hash_lock);
3022                         }
3023                         if (exists != NULL) {
3024                                 /* somebody beat us to the hash insert */
3025                                 mutex_exit(hash_lock);
3026                                 buf_discard_identity(hdr);
3027                                 (void) arc_buf_remove_ref(buf, private);
3028                                 goto top; /* restart the IO request */
3029                         }
3030                         /* if this is a prefetch, we don't have a reference */
3031                         if (*arc_flags & ARC_PREFETCH) {
3032                                 (void) remove_reference(hdr, hash_lock,
3033                                     private);
3034                                 hdr->b_flags |= ARC_PREFETCH;
3035                         }
3036                         if (*arc_flags & ARC_L2CACHE)
3037                                 hdr->b_flags |= ARC_L2CACHE;
3038                         if (*arc_flags & ARC_L2COMPRESS)
3039                                 hdr->b_flags |= ARC_L2COMPRESS;
3040                         if (BP_GET_LEVEL(bp) > 0)
3041                                 hdr->b_flags |= ARC_INDIRECT;
3042                 } else {
3043                         /* this block is in the ghost cache */
3044                         ASSERT(GHOST_STATE(hdr->b_state));
3045                         ASSERT(!HDR_IO_IN_PROGRESS(hdr));
3046                         ASSERT0(refcount_count(&hdr->b_refcnt));
3047                         ASSERT(hdr->b_buf == NULL);
3048 
3049                         /* if this is a prefetch, we don't have a reference */
3050                         if (*arc_flags & ARC_PREFETCH)
3051                                 hdr->b_flags |= ARC_PREFETCH;
3052                         else
3053                                 add_reference(hdr, hash_lock, private);
3054                         if (*arc_flags & ARC_L2CACHE)
3055                                 hdr->b_flags |= ARC_L2CACHE;
3056                         if (*arc_flags & ARC_L2COMPRESS)
3057                                 hdr->b_flags |= ARC_L2COMPRESS;
3058                         buf = kmem_cache_alloc(buf_cache, KM_PUSHPAGE);
3059                         buf->b_hdr = hdr;
3060                         buf->b_data = NULL;
3061                         buf->b_efunc = NULL;
3062                         buf->b_private = NULL;
3063                         buf->b_next = NULL;
3064                         hdr->b_buf = buf;
3065                         ASSERT(hdr->b_datacnt == 0);
3066                         hdr->b_datacnt = 1;
3067                         arc_get_data_buf(buf);
3068                         arc_access(hdr, hash_lock);
3069                 }
3070 
3071                 ASSERT(!GHOST_STATE(hdr->b_state));
3072 
3073                 acb = kmem_zalloc(sizeof (arc_callback_t), KM_SLEEP);
3074                 acb->acb_done = done;
3075                 acb->acb_private = private;
3076 
3077                 ASSERT(hdr->b_acb == NULL);
3078                 hdr->b_acb = acb;
3079                 hdr->b_flags |= ARC_IO_IN_PROGRESS;
3080 
3081                 if (hdr->b_l2hdr != NULL &&
3082                     (vd = hdr->b_l2hdr->b_dev->l2ad_vdev) != NULL) {
3083                         devw = hdr->b_l2hdr->b_dev->l2ad_writing;
3084                         addr = hdr->b_l2hdr->b_daddr;
3085                         b_compress = hdr->b_l2hdr->b_compress;
3086                         b_asize = hdr->b_l2hdr->b_asize;
3087                         /*
3088                          * Lock out device removal.
3089                          */
3090                         if (vdev_is_dead(vd) ||
3091                             !spa_config_tryenter(spa, SCL_L2ARC, vd, RW_READER))
3092                                 vd = NULL;
3093                 }
3094 
3095                 if (hash_lock != NULL)
3096                         mutex_exit(hash_lock);
3097 
3098                 /*
3099                  * At this point, we have a level 1 cache miss.  Try again in
3100                  * L2ARC if possible.
3101                  */
3102                 ASSERT3U(hdr->b_size, ==, size);
3103                 DTRACE_PROBE4(arc__miss, arc_buf_hdr_t *, hdr, blkptr_t *, bp,
3104                     uint64_t, size, zbookmark_phys_t *, zb);
3105                 ARCSTAT_BUMP(arcstat_misses);
3106                 ARCSTAT_CONDSTAT(!(hdr->b_flags & ARC_PREFETCH),
3107                     demand, prefetch, hdr->b_type != ARC_BUFC_METADATA,
3108                     data, metadata, misses);
3109 
3110                 if (vd != NULL && l2arc_ndev != 0 && !(l2arc_norw && devw)) {
3111                         /*
3112                          * Read from the L2ARC if the following are true:
3113                          * 1. The L2ARC vdev was previously cached.
3114                          * 2. This buffer still has L2ARC metadata.
3115                          * 3. This buffer isn't currently writing to the L2ARC.
3116                          * 4. The L2ARC entry wasn't evicted, which may
3117                          *    also have invalidated the vdev.
3118                          * 5. This isn't prefetch and l2arc_noprefetch is set.
3119                          */
3120                         if (hdr->b_l2hdr != NULL &&
3121                             !HDR_L2_WRITING(hdr) && !HDR_L2_EVICTED(hdr) &&
3122                             !(l2arc_noprefetch && HDR_PREFETCH(hdr))) {
3123                                 l2arc_read_callback_t *cb;
3124 
3125                                 DTRACE_PROBE1(l2arc__hit, arc_buf_hdr_t *, hdr);
3126                                 ARCSTAT_BUMP(arcstat_l2_hits);
3127 
3128                                 cb = kmem_zalloc(sizeof (l2arc_read_callback_t),
3129                                     KM_SLEEP);
3130                                 cb->l2rcb_buf = buf;
3131                                 cb->l2rcb_spa = spa;
3132                                 cb->l2rcb_bp = *bp;
3133                                 cb->l2rcb_zb = *zb;
3134                                 cb->l2rcb_flags = zio_flags;
3135                                 cb->l2rcb_compress = b_compress;
3136 
3137                                 ASSERT(addr >= VDEV_LABEL_START_SIZE &&
3138                                     addr + size < vd->vdev_psize -
3139                                     VDEV_LABEL_END_SIZE);
3140 
3141                                 /*
3142                                  * l2arc read.  The SCL_L2ARC lock will be
3143                                  * released by l2arc_read_done().
3144                                  * Issue a null zio if the underlying buffer
3145                                  * was squashed to zero size by compression.
3146                                  */
3147                                 if (b_compress == ZIO_COMPRESS_EMPTY) {
3148                                         rzio = zio_null(pio, spa, vd,
3149                                             l2arc_read_done, cb,
3150                                             zio_flags | ZIO_FLAG_DONT_CACHE |
3151                                             ZIO_FLAG_CANFAIL |
3152                                             ZIO_FLAG_DONT_PROPAGATE |
3153                                             ZIO_FLAG_DONT_RETRY);
3154                                 } else {
3155                                         rzio = zio_read_phys(pio, vd, addr,
3156                                             b_asize, buf->b_data,
3157                                             ZIO_CHECKSUM_OFF,
3158                                             l2arc_read_done, cb, priority,
3159                                             zio_flags | ZIO_FLAG_DONT_CACHE |
3160                                             ZIO_FLAG_CANFAIL |
3161                                             ZIO_FLAG_DONT_PROPAGATE |
3162                                             ZIO_FLAG_DONT_RETRY, B_FALSE);
3163                                 }
3164                                 DTRACE_PROBE2(l2arc__read, vdev_t *, vd,
3165                                     zio_t *, rzio);
3166                                 ARCSTAT_INCR(arcstat_l2_read_bytes, b_asize);
3167 
3168                                 if (*arc_flags & ARC_NOWAIT) {
3169                                         zio_nowait(rzio);
3170                                         return (0);
3171                                 }
3172 
3173                                 ASSERT(*arc_flags & ARC_WAIT);
3174                                 if (zio_wait(rzio) == 0)
3175                                         return (0);
3176 
3177                                 /* l2arc read error; goto zio_read() */
3178                         } else {
3179                                 DTRACE_PROBE1(l2arc__miss,
3180                                     arc_buf_hdr_t *, hdr);
3181                                 ARCSTAT_BUMP(arcstat_l2_misses);
3182                                 if (HDR_L2_WRITING(hdr))
3183                                         ARCSTAT_BUMP(arcstat_l2_rw_clash);
3184                                 spa_config_exit(spa, SCL_L2ARC, vd);
3185                         }
3186                 } else {
3187                         if (vd != NULL)
3188                                 spa_config_exit(spa, SCL_L2ARC, vd);
3189                         if (l2arc_ndev != 0) {
3190                                 DTRACE_PROBE1(l2arc__miss,
3191                                     arc_buf_hdr_t *, hdr);
3192                                 ARCSTAT_BUMP(arcstat_l2_misses);
3193                         }
3194                 }
3195 
3196                 rzio = zio_read(pio, spa, bp, buf->b_data, size,
3197                     arc_read_done, buf, priority, zio_flags, zb);
3198 
3199                 if (*arc_flags & ARC_WAIT)
3200                         return (zio_wait(rzio));
3201 
3202                 ASSERT(*arc_flags & ARC_NOWAIT);
3203                 zio_nowait(rzio);
3204         }
3205         return (0);
3206 }
3207 
3208 void
3209 arc_set_callback(arc_buf_t *buf, arc_evict_func_t *func, void *private)
3210 {
3211         ASSERT(buf->b_hdr != NULL);
3212         ASSERT(buf->b_hdr->b_state != arc_anon);
3213         ASSERT(!refcount_is_zero(&buf->b_hdr->b_refcnt) || func == NULL);
3214         ASSERT(buf->b_efunc == NULL);
3215         ASSERT(!HDR_BUF_AVAILABLE(buf->b_hdr));
3216 
3217         buf->b_efunc = func;
3218         buf->b_private = private;
3219 }
3220 
3221 /*
3222  * Notify the arc that a block was freed, and thus will never be used again.
3223  */
3224 void
3225 arc_freed(spa_t *spa, const blkptr_t *bp)
3226 {
3227         arc_buf_hdr_t *hdr;
3228         kmutex_t *hash_lock;
3229         uint64_t guid = spa_load_guid(spa);
3230 
3231         ASSERT(!BP_IS_EMBEDDED(bp));
3232 
3233         hdr = buf_hash_find(guid, bp, &hash_lock);
3234         if (hdr == NULL)
3235                 return;
3236         if (HDR_BUF_AVAILABLE(hdr)) {
3237                 arc_buf_t *buf = hdr->b_buf;
3238                 add_reference(hdr, hash_lock, FTAG);
3239                 hdr->b_flags &= ~ARC_BUF_AVAILABLE;
3240                 mutex_exit(hash_lock);
3241 
3242                 arc_release(buf, FTAG);
3243                 (void) arc_buf_remove_ref(buf, FTAG);
3244         } else {
3245                 mutex_exit(hash_lock);
3246         }
3247 
3248 }
3249 
3250 /*
3251  * Clear the user eviction callback set by arc_set_callback(), first calling
3252  * it if it exists.  Because the presence of a callback keeps an arc_buf cached
3253  * clearing the callback may result in the arc_buf being destroyed.  However,
3254  * it will not result in the *last* arc_buf being destroyed, hence the data
3255  * will remain cached in the ARC. We make a copy of the arc buffer here so
3256  * that we can process the callback without holding any locks.
3257  *
3258  * It's possible that the callback is already in the process of being cleared
3259  * by another thread.  In this case we can not clear the callback.
3260  *
3261  * Returns B_TRUE if the callback was successfully called and cleared.
3262  */
3263 boolean_t
3264 arc_clear_callback(arc_buf_t *buf)
3265 {
3266         arc_buf_hdr_t *hdr;
3267         kmutex_t *hash_lock;
3268         arc_evict_func_t *efunc = buf->b_efunc;
3269         void *private = buf->b_private;
3270 
3271         mutex_enter(&buf->b_evict_lock);
3272         hdr = buf->b_hdr;
3273         if (hdr == NULL) {
3274                 /*
3275                  * We are in arc_do_user_evicts().
3276                  */
3277                 ASSERT(buf->b_data == NULL);
3278                 mutex_exit(&buf->b_evict_lock);
3279                 return (B_FALSE);
3280         } else if (buf->b_data == NULL) {
3281                 /*
3282                  * We are on the eviction list; process this buffer now
3283                  * but let arc_do_user_evicts() do the reaping.
3284                  */
3285                 buf->b_efunc = NULL;
3286                 mutex_exit(&buf->b_evict_lock);
3287                 VERIFY0(efunc(private));
3288                 return (B_TRUE);
3289         }
3290         hash_lock = HDR_LOCK(hdr);
3291         mutex_enter(hash_lock);
3292         hdr = buf->b_hdr;
3293         ASSERT3P(hash_lock, ==, HDR_LOCK(hdr));
3294 
3295         ASSERT3U(refcount_count(&hdr->b_refcnt), <, hdr->b_datacnt);
3296         ASSERT(hdr->b_state == arc_mru || hdr->b_state == arc_mfu);
3297 
3298         buf->b_efunc = NULL;
3299         buf->b_private = NULL;
3300 
3301         if (hdr->b_datacnt > 1) {
3302                 mutex_exit(&buf->b_evict_lock);
3303                 arc_buf_destroy(buf, FALSE, TRUE);
3304         } else {
3305                 ASSERT(buf == hdr->b_buf);
3306                 hdr->b_flags |= ARC_BUF_AVAILABLE;
3307                 mutex_exit(&buf->b_evict_lock);
3308         }
3309 
3310         mutex_exit(hash_lock);
3311         VERIFY0(efunc(private));
3312         return (B_TRUE);
3313 }
3314 
3315 /*
3316  * Release this buffer from the cache, making it an anonymous buffer.  This
3317  * must be done after a read and prior to modifying the buffer contents.
3318  * If the buffer has more than one reference, we must make
3319  * a new hdr for the buffer.
3320  */
3321 void
3322 arc_release(arc_buf_t *buf, void *tag)
3323 {
3324         arc_buf_hdr_t *hdr;
3325         kmutex_t *hash_lock = NULL;
3326         l2arc_buf_hdr_t *l2hdr;
3327         uint64_t buf_size;
3328 
3329         /*
3330          * It would be nice to assert that if it's DMU metadata (level >
3331          * 0 || it's the dnode file), then it must be syncing context.
3332          * But we don't know that information at this level.
3333          */
3334 
3335         mutex_enter(&buf->b_evict_lock);
3336         hdr = buf->b_hdr;
3337 
3338         /* this buffer is not on any list */
3339         ASSERT(refcount_count(&hdr->b_refcnt) > 0);
3340 
3341         if (hdr->b_state == arc_anon) {
3342                 /* this buffer is already released */
3343                 ASSERT(buf->b_efunc == NULL);
3344         } else {
3345                 hash_lock = HDR_LOCK(hdr);
3346                 mutex_enter(hash_lock);
3347                 hdr = buf->b_hdr;
3348                 ASSERT3P(hash_lock, ==, HDR_LOCK(hdr));
3349         }
3350 
3351         l2hdr = hdr->b_l2hdr;
3352         if (l2hdr) {
3353                 mutex_enter(&l2arc_buflist_mtx);
3354                 hdr->b_l2hdr = NULL;
3355                 list_remove(l2hdr->b_dev->l2ad_buflist, hdr);
3356         }
3357         buf_size = hdr->b_size;
3358 
3359         /*
3360          * Do we have more than one buf?
3361          */
3362         if (hdr->b_datacnt > 1) {
3363                 arc_buf_hdr_t *nhdr;
3364                 arc_buf_t **bufp;
3365                 uint64_t blksz = hdr->b_size;
3366                 uint64_t spa = hdr->b_spa;
3367                 arc_buf_contents_t type = hdr->b_type;
3368                 uint32_t flags = hdr->b_flags;
3369 
3370                 ASSERT(hdr->b_buf != buf || buf->b_next != NULL);
3371                 /*
3372                  * Pull the data off of this hdr and attach it to
3373                  * a new anonymous hdr.
3374                  */
3375                 (void) remove_reference(hdr, hash_lock, tag);
3376                 bufp = &hdr->b_buf;
3377                 while (*bufp != buf)
3378                         bufp = &(*bufp)->b_next;
3379                 *bufp = buf->b_next;
3380                 buf->b_next = NULL;
3381 
3382                 ASSERT3U(hdr->b_state->arcs_size, >=, hdr->b_size);
3383                 atomic_add_64(&hdr->b_state->arcs_size, -hdr->b_size);
3384                 if (refcount_is_zero(&hdr->b_refcnt)) {
3385                         uint64_t *size = &hdr->b_state->arcs_lsize[hdr->b_type];
3386                         ASSERT3U(*size, >=, hdr->b_size);
3387                         atomic_add_64(size, -hdr->b_size);
3388                 }
3389 
3390                 /*
3391                  * We're releasing a duplicate user data buffer, update
3392                  * our statistics accordingly.
3393                  */
3394                 if (hdr->b_type == ARC_BUFC_DATA) {
3395                         ARCSTAT_BUMPDOWN(arcstat_duplicate_buffers);
3396                         ARCSTAT_INCR(arcstat_duplicate_buffers_size,
3397                             -hdr->b_size);
3398                 }
3399                 hdr->b_datacnt -= 1;
3400                 arc_cksum_verify(buf);
3401                 arc_buf_unwatch(buf);
3402 
3403                 mutex_exit(hash_lock);
3404 
3405                 nhdr = kmem_cache_alloc(hdr_cache, KM_PUSHPAGE);
3406                 nhdr->b_size = blksz;
3407                 nhdr->b_spa = spa;
3408                 nhdr->b_type = type;
3409                 nhdr->b_buf = buf;
3410                 nhdr->b_state = arc_anon;
3411                 nhdr->b_arc_access = 0;
3412                 nhdr->b_flags = flags & ARC_L2_WRITING;
3413                 nhdr->b_l2hdr = NULL;
3414                 nhdr->b_datacnt = 1;
3415                 nhdr->b_freeze_cksum = NULL;
3416                 (void) refcount_add(&nhdr->b_refcnt, tag);
3417                 buf->b_hdr = nhdr;
3418                 mutex_exit(&buf->b_evict_lock);
3419                 atomic_add_64(&arc_anon->arcs_size, blksz);
3420         } else {
3421                 mutex_exit(&buf->b_evict_lock);
3422                 ASSERT(refcount_count(&hdr->b_refcnt) == 1);
3423                 ASSERT(!list_link_active(&hdr->b_arc_node));
3424                 ASSERT(!HDR_IO_IN_PROGRESS(hdr));
3425                 if (hdr->b_state != arc_anon)
3426                         arc_change_state(arc_anon, hdr, hash_lock);
3427                 hdr->b_arc_access = 0;
3428                 if (hash_lock)
3429                         mutex_exit(hash_lock);
3430 
3431                 buf_discard_identity(hdr);
3432                 arc_buf_thaw(buf);
3433         }
3434         buf->b_efunc = NULL;
3435         buf->b_private = NULL;
3436 
3437         if (l2hdr) {
3438                 ARCSTAT_INCR(arcstat_l2_asize, -l2hdr->b_asize);
3439                 vdev_space_update(l2hdr->b_dev->l2ad_vdev,
3440                     -l2hdr->b_asize, 0, 0);
3441                 kmem_free(l2hdr, sizeof (l2arc_buf_hdr_t));
3442                 ARCSTAT_INCR(arcstat_l2_size, -buf_size);
3443                 mutex_exit(&l2arc_buflist_mtx);
3444         }
3445 }
3446 
3447 int
3448 arc_released(arc_buf_t *buf)
3449 {
3450         int released;
3451 
3452         mutex_enter(&buf->b_evict_lock);
3453         released = (buf->b_data != NULL && buf->b_hdr->b_state == arc_anon);
3454         mutex_exit(&buf->b_evict_lock);
3455         return (released);
3456 }
3457 
3458 #ifdef ZFS_DEBUG
3459 int
3460 arc_referenced(arc_buf_t *buf)
3461 {
3462         int referenced;
3463 
3464         mutex_enter(&buf->b_evict_lock);
3465         referenced = (refcount_count(&buf->b_hdr->b_refcnt));
3466         mutex_exit(&buf->b_evict_lock);
3467         return (referenced);
3468 }
3469 #endif
3470 
3471 static void
3472 arc_write_ready(zio_t *zio)
3473 {
3474         arc_write_callback_t *callback = zio->io_private;
3475         arc_buf_t *buf = callback->awcb_buf;
3476         arc_buf_hdr_t *hdr = buf->b_hdr;
3477 
3478         ASSERT(!refcount_is_zero(&buf->b_hdr->b_refcnt));
3479         callback->awcb_ready(zio, buf, callback->awcb_private);
3480 
3481         /*
3482          * If the IO is already in progress, then this is a re-write
3483          * attempt, so we need to thaw and re-compute the cksum.
3484          * It is the responsibility of the callback to handle the
3485          * accounting for any re-write attempt.
3486          */
3487         if (HDR_IO_IN_PROGRESS(hdr)) {
3488                 mutex_enter(&hdr->b_freeze_lock);
3489                 if (hdr->b_freeze_cksum != NULL) {
3490                         kmem_free(hdr->b_freeze_cksum, sizeof (zio_cksum_t));
3491                         hdr->b_freeze_cksum = NULL;
3492                 }
3493                 mutex_exit(&hdr->b_freeze_lock);
3494         }
3495         arc_cksum_compute(buf, B_FALSE);
3496         hdr->b_flags |= ARC_IO_IN_PROGRESS;
3497 }
3498 
3499 /*
3500  * The SPA calls this callback for each physical write that happens on behalf
3501  * of a logical write.  See the comment in dbuf_write_physdone() for details.
3502  */
3503 static void
3504 arc_write_physdone(zio_t *zio)
3505 {
3506         arc_write_callback_t *cb = zio->io_private;
3507         if (cb->awcb_physdone != NULL)
3508                 cb->awcb_physdone(zio, cb->awcb_buf, cb->awcb_private);
3509 }
3510 
3511 static void
3512 arc_write_done(zio_t *zio)
3513 {
3514         arc_write_callback_t *callback = zio->io_private;
3515         arc_buf_t *buf = callback->awcb_buf;
3516         arc_buf_hdr_t *hdr = buf->b_hdr;
3517 
3518         ASSERT(hdr->b_acb == NULL);
3519 
3520         if (zio->io_error == 0) {
3521                 if (BP_IS_HOLE(zio->io_bp) || BP_IS_EMBEDDED(zio->io_bp)) {
3522                         buf_discard_identity(hdr);
3523                 } else {
3524                         hdr->b_dva = *BP_IDENTITY(zio->io_bp);
3525                         hdr->b_birth = BP_PHYSICAL_BIRTH(zio->io_bp);
3526                         hdr->b_cksum0 = zio->io_bp->blk_cksum.zc_word[0];
3527                 }
3528         } else {
3529                 ASSERT(BUF_EMPTY(hdr));
3530         }
3531 
3532         /*
3533          * If the block to be written was all-zero or compressed enough to be
3534          * embedded in the BP, no write was performed so there will be no
3535          * dva/birth/checksum.  The buffer must therefore remain anonymous
3536          * (and uncached).
3537          */
3538         if (!BUF_EMPTY(hdr)) {
3539                 arc_buf_hdr_t *exists;
3540                 kmutex_t *hash_lock;
3541 
3542                 ASSERT(zio->io_error == 0);
3543 
3544                 arc_cksum_verify(buf);
3545 
3546                 exists = buf_hash_insert(hdr, &hash_lock);
3547                 if (exists) {
3548                         /*
3549                          * This can only happen if we overwrite for
3550                          * sync-to-convergence, because we remove
3551                          * buffers from the hash table when we arc_free().
3552                          */
3553                         if (zio->io_flags & ZIO_FLAG_IO_REWRITE) {
3554                                 if (!BP_EQUAL(&zio->io_bp_orig, zio->io_bp))
3555                                         panic("bad overwrite, hdr=%p exists=%p",
3556                                             (void *)hdr, (void *)exists);
3557                                 ASSERT(refcount_is_zero(&exists->b_refcnt));
3558                                 arc_change_state(arc_anon, exists, hash_lock);
3559                                 mutex_exit(hash_lock);
3560                                 arc_hdr_destroy(exists);
3561                                 exists = buf_hash_insert(hdr, &hash_lock);
3562                                 ASSERT3P(exists, ==, NULL);
3563                         } else if (zio->io_flags & ZIO_FLAG_NOPWRITE) {
3564                                 /* nopwrite */
3565                                 ASSERT(zio->io_prop.zp_nopwrite);
3566                                 if (!BP_EQUAL(&zio->io_bp_orig, zio->io_bp))
3567                                         panic("bad nopwrite, hdr=%p exists=%p",
3568                                             (void *)hdr, (void *)exists);
3569                         } else {
3570                                 /* Dedup */
3571                                 ASSERT(hdr->b_datacnt == 1);
3572                                 ASSERT(hdr->b_state == arc_anon);
3573                                 ASSERT(BP_GET_DEDUP(zio->io_bp));
3574                                 ASSERT(BP_GET_LEVEL(zio->io_bp) == 0);
3575                         }
3576                 }
3577                 hdr->b_flags &= ~ARC_IO_IN_PROGRESS;
3578                 /* if it's not anon, we are doing a scrub */
3579                 if (!exists && hdr->b_state == arc_anon)
3580                         arc_access(hdr, hash_lock);
3581                 mutex_exit(hash_lock);
3582         } else {
3583                 hdr->b_flags &= ~ARC_IO_IN_PROGRESS;
3584         }
3585 
3586         ASSERT(!refcount_is_zero(&hdr->b_refcnt));
3587         callback->awcb_done(zio, buf, callback->awcb_private);
3588 
3589         kmem_free(callback, sizeof (arc_write_callback_t));
3590 }
3591 
3592 zio_t *
3593 arc_write(zio_t *pio, spa_t *spa, uint64_t txg,
3594     blkptr_t *bp, arc_buf_t *buf, boolean_t l2arc, boolean_t l2arc_compress,
3595     const zio_prop_t *zp, arc_done_func_t *ready, arc_done_func_t *physdone,
3596     arc_done_func_t *done, void *private, zio_priority_t priority,
3597     int zio_flags, const zbookmark_phys_t *zb)
3598 {
3599         arc_buf_hdr_t *hdr = buf->b_hdr;
3600         arc_write_callback_t *callback;
3601         zio_t *zio;
3602 
3603         ASSERT(ready != NULL);
3604         ASSERT(done != NULL);
3605         ASSERT(!HDR_IO_ERROR(hdr));
3606         ASSERT((hdr->b_flags & ARC_IO_IN_PROGRESS) == 0);
3607         ASSERT(hdr->b_acb == NULL);
3608         if (l2arc)
3609                 hdr->b_flags |= ARC_L2CACHE;
3610         if (l2arc_compress)
3611                 hdr->b_flags |= ARC_L2COMPRESS;
3612         callback = kmem_zalloc(sizeof (arc_write_callback_t), KM_SLEEP);
3613         callback->awcb_ready = ready;
3614         callback->awcb_physdone = physdone;
3615         callback->awcb_done = done;
3616         callback->awcb_private = private;
3617         callback->awcb_buf = buf;
3618 
3619         zio = zio_write(pio, spa, txg, bp, buf->b_data, hdr->b_size, zp,
3620             arc_write_ready, arc_write_physdone, arc_write_done, callback,
3621             priority, zio_flags, zb);
3622 
3623         return (zio);
3624 }
3625 
3626 static int
3627 arc_memory_throttle(uint64_t reserve, uint64_t txg)
3628 {
3629 #ifdef _KERNEL
3630         uint64_t available_memory = ptob(freemem);
3631         static uint64_t page_load = 0;
3632         static uint64_t last_txg = 0;
3633 
3634 #if defined(__i386)
3635         available_memory =
3636             MIN(available_memory, vmem_size(heap_arena, VMEM_FREE));
3637 #endif
3638 
3639         if (freemem > physmem * arc_lotsfree_percent / 100)
3640                 return (0);
3641 
3642         if (txg > last_txg) {
3643                 last_txg = txg;
3644                 page_load = 0;
3645         }
3646         /*
3647          * If we are in pageout, we know that memory is already tight,
3648          * the arc is already going to be evicting, so we just want to
3649          * continue to let page writes occur as quickly as possible.
3650          */
3651         if (curproc == proc_pageout) {
3652                 if (page_load > MAX(ptob(minfree), available_memory) / 4)
3653                         return (SET_ERROR(ERESTART));
3654                 /* Note: reserve is inflated, so we deflate */
3655                 page_load += reserve / 8;
3656                 return (0);
3657         } else if (page_load > 0 && arc_reclaim_needed()) {
3658                 /* memory is low, delay before restarting */
3659                 ARCSTAT_INCR(arcstat_memory_throttle_count, 1);
3660                 return (SET_ERROR(EAGAIN));
3661         }
3662         page_load = 0;
3663 #endif
3664         return (0);
3665 }
3666 
3667 void
3668 arc_tempreserve_clear(uint64_t reserve)
3669 {
3670         atomic_add_64(&arc_tempreserve, -reserve);
3671         ASSERT((int64_t)arc_tempreserve >= 0);
3672 }
3673 
3674 int
3675 arc_tempreserve_space(uint64_t reserve, uint64_t txg)
3676 {
3677         int error;
3678         uint64_t anon_size;
3679 
3680         if (reserve > arc_c/4 && !arc_no_grow)
3681                 arc_c = MIN(arc_c_max, reserve * 4);
3682         if (reserve > arc_c)
3683                 return (SET_ERROR(ENOMEM));
3684 
3685         /*
3686          * Don't count loaned bufs as in flight dirty data to prevent long
3687          * network delays from blocking transactions that are ready to be
3688          * assigned to a txg.
3689          */
3690         anon_size = MAX((int64_t)(arc_anon->arcs_size - arc_loaned_bytes), 0);
3691 
3692         /*
3693          * Writes will, almost always, require additional memory allocations
3694          * in order to compress/encrypt/etc the data.  We therefore need to
3695          * make sure that there is sufficient available memory for this.
3696          */
3697         error = arc_memory_throttle(reserve, txg);
3698         if (error != 0)
3699                 return (error);
3700 
3701         /*
3702          * Throttle writes when the amount of dirty data in the cache
3703          * gets too large.  We try to keep the cache less than half full
3704          * of dirty blocks so that our sync times don't grow too large.
3705          * Note: if two requests come in concurrently, we might let them
3706          * both succeed, when one of them should fail.  Not a huge deal.
3707          */
3708 
3709         if (reserve + arc_tempreserve + anon_size > arc_c / 2 &&
3710             anon_size > arc_c / 4) {
3711                 dprintf("failing, arc_tempreserve=%lluK anon_meta=%lluK "
3712                     "anon_data=%lluK tempreserve=%lluK arc_c=%lluK\n",
3713                     arc_tempreserve>>10,
3714                     arc_anon->arcs_lsize[ARC_BUFC_METADATA]>>10,
3715                     arc_anon->arcs_lsize[ARC_BUFC_DATA]>>10,
3716                     reserve>>10, arc_c>>10);
3717                 return (SET_ERROR(ERESTART));
3718         }
3719         atomic_add_64(&arc_tempreserve, reserve);
3720         return (0);
3721 }
3722 
3723 void
3724 arc_init(void)
3725 {
3726         mutex_init(&arc_reclaim_thr_lock, NULL, MUTEX_DEFAULT, NULL);
3727         cv_init(&arc_reclaim_thr_cv, NULL, CV_DEFAULT, NULL);
3728 
3729         /* Convert seconds to clock ticks */
3730         arc_min_prefetch_lifespan = 1 * hz;
3731 
3732         /* Start out with 1/8 of all memory */
3733         arc_c = physmem * PAGESIZE / 8;
3734 
3735 #ifdef _KERNEL
3736         /*
3737          * On architectures where the physical memory can be larger
3738          * than the addressable space (intel in 32-bit mode), we may
3739          * need to limit the cache to 1/8 of VM size.
3740          */
3741         arc_c = MIN(arc_c, vmem_size(heap_arena, VMEM_ALLOC | VMEM_FREE) / 8);
3742 #endif
3743 
3744         /* set min cache to 1/32 of all memory, or 64MB, whichever is more */
3745         arc_c_min = MAX(arc_c / 4, 64<<20);
3746         /* set max to 3/4 of all memory, or all but 1GB, whichever is more */
3747         if (arc_c * 8 >= 1<<30)
3748                 arc_c_max = (arc_c * 8) - (1<<30);
3749         else
3750                 arc_c_max = arc_c_min;
3751         arc_c_max = MAX(arc_c * 6, arc_c_max);
3752 
3753         /*
3754          * Allow the tunables to override our calculations if they are
3755          * reasonable (ie. over 64MB)
3756          */
3757         if (zfs_arc_max > 64<<20 && zfs_arc_max < physmem * PAGESIZE)
3758                 arc_c_max = zfs_arc_max;
3759         if (zfs_arc_min > 64<<20 && zfs_arc_min <= arc_c_max)
3760                 arc_c_min = zfs_arc_min;
3761 
3762         arc_c = arc_c_max;
3763         arc_p = (arc_c >> 1);
3764 
3765         /* limit meta-data to 1/4 of the arc capacity */
3766         arc_meta_limit = arc_c_max / 4;
3767 
3768         /* Allow the tunable to override if it is reasonable */
3769         if (zfs_arc_meta_limit > 0 && zfs_arc_meta_limit <= arc_c_max)
3770                 arc_meta_limit = zfs_arc_meta_limit;
3771 
3772         if (arc_c_min < arc_meta_limit / 2 && zfs_arc_min == 0)
3773                 arc_c_min = arc_meta_limit / 2;
3774 
3775         if (zfs_arc_grow_retry > 0)
3776                 arc_grow_retry = zfs_arc_grow_retry;
3777 
3778         if (zfs_arc_shrink_shift > 0)
3779                 arc_shrink_shift = zfs_arc_shrink_shift;
3780 
3781         if (zfs_arc_p_min_shift > 0)
3782                 arc_p_min_shift = zfs_arc_p_min_shift;
3783 
3784         /* if kmem_flags are set, lets try to use less memory */
3785         if (kmem_debugging())
3786                 arc_c = arc_c / 2;
3787         if (arc_c < arc_c_min)
3788                 arc_c = arc_c_min;
3789 
3790         arc_anon = &ARC_anon;
3791         arc_mru = &ARC_mru;
3792         arc_mru_ghost = &ARC_mru_ghost;
3793         arc_mfu = &ARC_mfu;
3794         arc_mfu_ghost = &ARC_mfu_ghost;
3795         arc_l2c_only = &ARC_l2c_only;
3796         arc_size = 0;
3797 
3798         mutex_init(&arc_anon->arcs_mtx, NULL, MUTEX_DEFAULT, NULL);
3799         mutex_init(&arc_mru->arcs_mtx, NULL, MUTEX_DEFAULT, NULL);
3800         mutex_init(&arc_mru_ghost->arcs_mtx, NULL, MUTEX_DEFAULT, NULL);
3801         mutex_init(&arc_mfu->arcs_mtx, NULL, MUTEX_DEFAULT, NULL);
3802         mutex_init(&arc_mfu_ghost->arcs_mtx, NULL, MUTEX_DEFAULT, NULL);
3803         mutex_init(&arc_l2c_only->arcs_mtx, NULL, MUTEX_DEFAULT, NULL);
3804 
3805         list_create(&arc_mru->arcs_list[ARC_BUFC_METADATA],
3806             sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node));
3807         list_create(&arc_mru->arcs_list[ARC_BUFC_DATA],
3808             sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node));
3809         list_create(&arc_mru_ghost->arcs_list[ARC_BUFC_METADATA],
3810             sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node));
3811         list_create(&arc_mru_ghost->arcs_list[ARC_BUFC_DATA],
3812             sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node));
3813         list_create(&arc_mfu->arcs_list[ARC_BUFC_METADATA],
3814             sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node));
3815         list_create(&arc_mfu->arcs_list[ARC_BUFC_DATA],
3816             sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node));
3817         list_create(&arc_mfu_ghost->arcs_list[ARC_BUFC_METADATA],
3818             sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node));
3819         list_create(&arc_mfu_ghost->arcs_list[ARC_BUFC_DATA],
3820             sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node));
3821         list_create(&arc_l2c_only->arcs_list[ARC_BUFC_METADATA],
3822             sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node));
3823         list_create(&arc_l2c_only->arcs_list[ARC_BUFC_DATA],
3824             sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node));
3825 
3826         buf_init();
3827 
3828         arc_thread_exit = 0;
3829         arc_eviction_list = NULL;
3830         mutex_init(&arc_eviction_mtx, NULL, MUTEX_DEFAULT, NULL);
3831         bzero(&arc_eviction_hdr, sizeof (arc_buf_hdr_t));
3832 
3833         arc_ksp = kstat_create("zfs", 0, "arcstats", "misc", KSTAT_TYPE_NAMED,
3834             sizeof (arc_stats) / sizeof (kstat_named_t), KSTAT_FLAG_VIRTUAL);
3835 
3836         if (arc_ksp != NULL) {
3837                 arc_ksp->ks_data = &arc_stats;
3838                 kstat_install(arc_ksp);
3839         }
3840 
3841         (void) thread_create(NULL, 0, arc_reclaim_thread, NULL, 0, &p0,
3842             TS_RUN, minclsyspri);
3843 
3844         arc_dead = FALSE;
3845         arc_warm = B_FALSE;
3846 
3847         /*
3848          * Calculate maximum amount of dirty data per pool.
3849          *
3850          * If it has been set by /etc/system, take that.
3851          * Otherwise, use a percentage of physical memory defined by
3852          * zfs_dirty_data_max_percent (default 10%) with a cap at
3853          * zfs_dirty_data_max_max (default 4GB).
3854          */
3855         if (zfs_dirty_data_max == 0) {
3856                 zfs_dirty_data_max = physmem * PAGESIZE *
3857                     zfs_dirty_data_max_percent / 100;
3858                 zfs_dirty_data_max = MIN(zfs_dirty_data_max,
3859                     zfs_dirty_data_max_max);
3860         }
3861 }
3862 
3863 void
3864 arc_fini(void)
3865 {
3866         mutex_enter(&arc_reclaim_thr_lock);
3867         arc_thread_exit = 1;
3868         while (arc_thread_exit != 0)
3869                 cv_wait(&arc_reclaim_thr_cv, &arc_reclaim_thr_lock);
3870         mutex_exit(&arc_reclaim_thr_lock);
3871 
3872         arc_flush(NULL);
3873 
3874         arc_dead = TRUE;
3875 
3876         if (arc_ksp != NULL) {
3877                 kstat_delete(arc_ksp);
3878                 arc_ksp = NULL;
3879         }
3880 
3881         mutex_destroy(&arc_eviction_mtx);
3882         mutex_destroy(&arc_reclaim_thr_lock);
3883         cv_destroy(&arc_reclaim_thr_cv);
3884 
3885         list_destroy(&arc_mru->arcs_list[ARC_BUFC_METADATA]);
3886         list_destroy(&arc_mru_ghost->arcs_list[ARC_BUFC_METADATA]);
3887         list_destroy(&arc_mfu->arcs_list[ARC_BUFC_METADATA]);
3888         list_destroy(&arc_mfu_ghost->arcs_list[ARC_BUFC_METADATA]);
3889         list_destroy(&arc_mru->arcs_list[ARC_BUFC_DATA]);
3890         list_destroy(&arc_mru_ghost->arcs_list[ARC_BUFC_DATA]);
3891         list_destroy(&arc_mfu->arcs_list[ARC_BUFC_DATA]);
3892         list_destroy(&arc_mfu_ghost->arcs_list[ARC_BUFC_DATA]);
3893 
3894         mutex_destroy(&arc_anon->arcs_mtx);
3895         mutex_destroy(&arc_mru->arcs_mtx);
3896         mutex_destroy(&arc_mru_ghost->arcs_mtx);
3897         mutex_destroy(&arc_mfu->arcs_mtx);
3898         mutex_destroy(&arc_mfu_ghost->arcs_mtx);
3899         mutex_destroy(&arc_l2c_only->arcs_mtx);
3900 
3901         buf_fini();
3902 
3903         ASSERT(arc_loaned_bytes == 0);
3904 }
3905 
3906 /*
3907  * Level 2 ARC
3908  *
3909  * The level 2 ARC (L2ARC) is a cache layer in-between main memory and disk.
3910  * It uses dedicated storage devices to hold cached data, which are populated
3911  * using large infrequent writes.  The main role of this cache is to boost
3912  * the performance of random read workloads.  The intended L2ARC devices
3913  * include short-stroked disks, solid state disks, and other media with
3914  * substantially faster read latency than disk.
3915  *
3916  *                 +-----------------------+
3917  *                 |         ARC           |
3918  *                 +-----------------------+
3919  *                    |         ^     ^
3920  *                    |         |     |
3921  *      l2arc_feed_thread()    arc_read()
3922  *                    |         |     |
3923  *                    |  l2arc read   |
3924  *                    V         |     |
3925  *               +---------------+    |
3926  *               |     L2ARC     |    |
3927  *               +---------------+    |
3928  *                   |    ^           |
3929  *          l2arc_write() |           |
3930  *                   |    |           |
3931  *                   V    |           |
3932  *                 +-------+      +-------+
3933  *                 | vdev  |      | vdev  |
3934  *                 | cache |      | cache |
3935  *                 +-------+      +-------+
3936  *                 +=========+     .-----.
3937  *                 :  L2ARC  :    |-_____-|
3938  *                 : devices :    | Disks |
3939  *                 +=========+    `-_____-'
3940  *
3941  * Read requests are satisfied from the following sources, in order:
3942  *
3943  *      1) ARC
3944  *      2) vdev cache of L2ARC devices
3945  *      3) L2ARC devices
3946  *      4) vdev cache of disks
3947  *      5) disks
3948  *
3949  * Some L2ARC device types exhibit extremely slow write performance.
3950  * To accommodate for this there are some significant differences between
3951  * the L2ARC and traditional cache design:
3952  *
3953  * 1. There is no eviction path from the ARC to the L2ARC.  Evictions from
3954  * the ARC behave as usual, freeing buffers and placing headers on ghost
3955  * lists.  The ARC does not send buffers to the L2ARC during eviction as
3956  * this would add inflated write latencies for all ARC memory pressure.
3957  *
3958  * 2. The L2ARC attempts to cache data from the ARC before it is evicted.
3959  * It does this by periodically scanning buffers from the eviction-end of
3960  * the MFU and MRU ARC lists, copying them to the L2ARC devices if they are
3961  * not already there. It scans until a headroom of buffers is satisfied,
3962  * which itself is a buffer for ARC eviction. If a compressible buffer is
3963  * found during scanning and selected for writing to an L2ARC device, we
3964  * temporarily boost scanning headroom during the next scan cycle to make
3965  * sure we adapt to compression effects (which might significantly reduce
3966  * the data volume we write to L2ARC). The thread that does this is
3967  * l2arc_feed_thread(), illustrated below; example sizes are included to
3968  * provide a better sense of ratio than this diagram:
3969  *
3970  *             head -->                        tail
3971  *              +---------------------+----------+
3972  *      ARC_mfu |:::::#:::::::::::::::|o#o###o###|-->.   # already on L2ARC
3973  *              +---------------------+----------+   |   o L2ARC eligible
3974  *      ARC_mru |:#:::::::::::::::::::|#o#ooo####|-->|   : ARC buffer
3975  *              +---------------------+----------+   |
3976  *                   15.9 Gbytes      ^ 32 Mbytes    |
3977  *                                 headroom          |
3978  *                                            l2arc_feed_thread()
3979  *                                                   |
3980  *                       l2arc write hand <--[oooo]--'
3981  *                               |           8 Mbyte
3982  *                               |          write max
3983  *                               V
3984  *                +==============================+
3985  *      L2ARC dev |####|#|###|###|    |####| ... |
3986  *                +==============================+
3987  *                           32 Gbytes
3988  *
3989  * 3. If an ARC buffer is copied to the L2ARC but then hit instead of
3990  * evicted, then the L2ARC has cached a buffer much sooner than it probably
3991  * needed to, potentially wasting L2ARC device bandwidth and storage.  It is
3992  * safe to say that this is an uncommon case, since buffers at the end of
3993  * the ARC lists have moved there due to inactivity.
3994  *
3995  * 4. If the ARC evicts faster than the L2ARC can maintain a headroom,
3996  * then the L2ARC simply misses copying some buffers.  This serves as a
3997  * pressure valve to prevent heavy read workloads from both stalling the ARC
3998  * with waits and clogging the L2ARC with writes.  This also helps prevent
3999  * the potential for the L2ARC to churn if it attempts to cache content too
4000  * quickly, such as during backups of the entire pool.
4001  *
4002  * 5. After system boot and before the ARC has filled main memory, there are
4003  * no evictions from the ARC and so the tails of the ARC_mfu and ARC_mru
4004  * lists can remain mostly static.  Instead of searching from tail of these
4005  * lists as pictured, the l2arc_feed_thread() will search from the list heads
4006  * for eligible buffers, greatly increasing its chance of finding them.
4007  *
4008  * The L2ARC device write speed is also boosted during this time so that
4009  * the L2ARC warms up faster.  Since there have been no ARC evictions yet,
4010  * there are no L2ARC reads, and no fear of degrading read performance
4011  * through increased writes.
4012  *
4013  * 6. Writes to the L2ARC devices are grouped and sent in-sequence, so that
4014  * the vdev queue can aggregate them into larger and fewer writes.  Each
4015  * device is written to in a rotor fashion, sweeping writes through
4016  * available space then repeating.
4017  *
4018  * 7. The L2ARC does not store dirty content.  It never needs to flush
4019  * write buffers back to disk based storage.
4020  *
4021  * 8. If an ARC buffer is written (and dirtied) which also exists in the
4022  * L2ARC, the now stale L2ARC buffer is immediately dropped.
4023  *
4024  * The performance of the L2ARC can be tweaked by a number of tunables, which
4025  * may be necessary for different workloads:
4026  *
4027  *      l2arc_write_max         max write bytes per interval
4028  *      l2arc_write_boost       extra write bytes during device warmup
4029  *      l2arc_noprefetch        skip caching prefetched buffers
4030  *      l2arc_headroom          number of max device writes to precache
4031  *      l2arc_headroom_boost    when we find compressed buffers during ARC
4032  *                              scanning, we multiply headroom by this
4033  *                              percentage factor for the next scan cycle,
4034  *                              since more compressed buffers are likely to
4035  *                              be present
4036  *      l2arc_feed_secs         seconds between L2ARC writing
4037  *
4038  * Tunables may be removed or added as future performance improvements are
4039  * integrated, and also may become zpool properties.
4040  *
4041  * There are three key functions that control how the L2ARC warms up:
4042  *
4043  *      l2arc_write_eligible()  check if a buffer is eligible to cache
4044  *      l2arc_write_size()      calculate how much to write
4045  *      l2arc_write_interval()  calculate sleep delay between writes
4046  *
4047  * These three functions determine what to write, how much, and how quickly
4048  * to send writes.
4049  */
4050 
4051 static boolean_t
4052 l2arc_write_eligible(uint64_t spa_guid, arc_buf_hdr_t *ab)
4053 {
4054         /*
4055          * A buffer is *not* eligible for the L2ARC if it:
4056          * 1. belongs to a different spa.
4057          * 2. is already cached on the L2ARC.
4058          * 3. has an I/O in progress (it may be an incomplete read).
4059          * 4. is flagged not eligible (zfs property).
4060          */
4061         if (ab->b_spa != spa_guid || ab->b_l2hdr != NULL ||
4062             HDR_IO_IN_PROGRESS(ab) || !HDR_L2CACHE(ab))
4063                 return (B_FALSE);
4064 
4065         return (B_TRUE);
4066 }
4067 
4068 static uint64_t
4069 l2arc_write_size(void)
4070 {
4071         uint64_t size;
4072 
4073         /*
4074          * Make sure our globals have meaningful values in case the user
4075          * altered them.
4076          */
4077         size = l2arc_write_max;
4078         if (size == 0) {
4079                 cmn_err(CE_NOTE, "Bad value for l2arc_write_max, value must "
4080                     "be greater than zero, resetting it to the default (%d)",
4081                     L2ARC_WRITE_SIZE);
4082                 size = l2arc_write_max = L2ARC_WRITE_SIZE;
4083         }
4084 
4085         if (arc_warm == B_FALSE)
4086                 size += l2arc_write_boost;
4087 
4088         return (size);
4089 
4090 }
4091 
4092 static clock_t
4093 l2arc_write_interval(clock_t began, uint64_t wanted, uint64_t wrote)
4094 {
4095         clock_t interval, next, now;
4096 
4097         /*
4098          * If the ARC lists are busy, increase our write rate; if the
4099          * lists are stale, idle back.  This is achieved by checking
4100          * how much we previously wrote - if it was more than half of
4101          * what we wanted, schedule the next write much sooner.
4102          */
4103         if (l2arc_feed_again && wrote > (wanted / 2))
4104                 interval = (hz * l2arc_feed_min_ms) / 1000;
4105         else
4106                 interval = hz * l2arc_feed_secs;
4107 
4108         now = ddi_get_lbolt();
4109         next = MAX(now, MIN(now + interval, began + interval));
4110 
4111         return (next);
4112 }
4113 
4114 static void
4115 l2arc_hdr_stat_add(void)
4116 {
4117         ARCSTAT_INCR(arcstat_l2_hdr_size, HDR_SIZE + L2HDR_SIZE);
4118         ARCSTAT_INCR(arcstat_hdr_size, -HDR_SIZE);
4119 }
4120 
4121 static void
4122 l2arc_hdr_stat_remove(void)
4123 {
4124         ARCSTAT_INCR(arcstat_l2_hdr_size, -(HDR_SIZE + L2HDR_SIZE));
4125         ARCSTAT_INCR(arcstat_hdr_size, HDR_SIZE);
4126 }
4127 
4128 /*
4129  * Cycle through L2ARC devices.  This is how L2ARC load balances.
4130  * If a device is returned, this also returns holding the spa config lock.
4131  */
4132 static l2arc_dev_t *
4133 l2arc_dev_get_next(void)
4134 {
4135         l2arc_dev_t *first, *next = NULL;
4136 
4137         /*
4138          * Lock out the removal of spas (spa_namespace_lock), then removal
4139          * of cache devices (l2arc_dev_mtx).  Once a device has been selected,
4140          * both locks will be dropped and a spa config lock held instead.
4141          */
4142         mutex_enter(&spa_namespace_lock);
4143         mutex_enter(&l2arc_dev_mtx);
4144 
4145         /* if there are no vdevs, there is nothing to do */
4146         if (l2arc_ndev == 0)
4147                 goto out;
4148 
4149         first = NULL;
4150         next = l2arc_dev_last;
4151         do {
4152                 /* loop around the list looking for a non-faulted vdev */
4153                 if (next == NULL) {
4154                         next = list_head(l2arc_dev_list);
4155                 } else {
4156                         next = list_next(l2arc_dev_list, next);
4157                         if (next == NULL)
4158                                 next = list_head(l2arc_dev_list);
4159                 }
4160 
4161                 /* if we have come back to the start, bail out */
4162                 if (first == NULL)
4163                         first = next;
4164                 else if (next == first)
4165                         break;
4166 
4167         } while (vdev_is_dead(next->l2ad_vdev));
4168 
4169         /* if we were unable to find any usable vdevs, return NULL */
4170         if (vdev_is_dead(next->l2ad_vdev))
4171                 next = NULL;
4172 
4173         l2arc_dev_last = next;
4174 
4175 out:
4176         mutex_exit(&l2arc_dev_mtx);
4177 
4178         /*
4179          * Grab the config lock to prevent the 'next' device from being
4180          * removed while we are writing to it.
4181          */
4182         if (next != NULL)
4183                 spa_config_enter(next->l2ad_spa, SCL_L2ARC, next, RW_READER);
4184         mutex_exit(&spa_namespace_lock);
4185 
4186         return (next);
4187 }
4188 
4189 /*
4190  * Free buffers that were tagged for destruction.
4191  */
4192 static void
4193 l2arc_do_free_on_write()
4194 {
4195         list_t *buflist;
4196         l2arc_data_free_t *df, *df_prev;
4197 
4198         mutex_enter(&l2arc_free_on_write_mtx);
4199         buflist = l2arc_free_on_write;
4200 
4201         for (df = list_tail(buflist); df; df = df_prev) {
4202                 df_prev = list_prev(buflist, df);
4203                 ASSERT(df->l2df_data != NULL);
4204                 ASSERT(df->l2df_func != NULL);
4205                 df->l2df_func(df->l2df_data, df->l2df_size);
4206                 list_remove(buflist, df);
4207                 kmem_free(df, sizeof (l2arc_data_free_t));
4208         }
4209 
4210         mutex_exit(&l2arc_free_on_write_mtx);
4211 }
4212 
4213 /*
4214  * A write to a cache device has completed.  Update all headers to allow
4215  * reads from these buffers to begin.
4216  */
4217 static void
4218 l2arc_write_done(zio_t *zio)
4219 {
4220         l2arc_write_callback_t *cb;
4221         l2arc_dev_t *dev;
4222         list_t *buflist;
4223         arc_buf_hdr_t *head, *ab, *ab_prev;
4224         l2arc_buf_hdr_t *abl2;
4225         kmutex_t *hash_lock;
4226         int64_t bytes_dropped = 0;
4227 
4228         cb = zio->io_private;
4229         ASSERT(cb != NULL);
4230         dev = cb->l2wcb_dev;
4231         ASSERT(dev != NULL);
4232         head = cb->l2wcb_head;
4233         ASSERT(head != NULL);
4234         buflist = dev->l2ad_buflist;
4235         ASSERT(buflist != NULL);
4236         DTRACE_PROBE2(l2arc__iodone, zio_t *, zio,
4237             l2arc_write_callback_t *, cb);
4238 
4239         if (zio->io_error != 0)
4240                 ARCSTAT_BUMP(arcstat_l2_writes_error);
4241 
4242         mutex_enter(&l2arc_buflist_mtx);
4243 
4244         /*
4245          * All writes completed, or an error was hit.
4246          */
4247         for (ab = list_prev(buflist, head); ab; ab = ab_prev) {
4248                 ab_prev = list_prev(buflist, ab);
4249                 abl2 = ab->b_l2hdr;
4250 
4251                 /*
4252                  * Release the temporary compressed buffer as soon as possible.
4253                  */
4254                 if (abl2->b_compress != ZIO_COMPRESS_OFF)
4255                         l2arc_release_cdata_buf(ab);
4256 
4257                 hash_lock = HDR_LOCK(ab);
4258                 if (!mutex_tryenter(hash_lock)) {
4259                         /*
4260                          * This buffer misses out.  It may be in a stage
4261                          * of eviction.  Its ARC_L2_WRITING flag will be
4262                          * left set, denying reads to this buffer.
4263                          */
4264                         ARCSTAT_BUMP(arcstat_l2_writes_hdr_miss);
4265                         continue;
4266                 }
4267 
4268                 if (zio->io_error != 0) {
4269                         /*
4270                          * Error - drop L2ARC entry.
4271                          */
4272                         list_remove(buflist, ab);
4273                         ARCSTAT_INCR(arcstat_l2_asize, -abl2->b_asize);
4274                         bytes_dropped += abl2->b_asize;
4275                         ab->b_l2hdr = NULL;
4276                         kmem_free(abl2, sizeof (l2arc_buf_hdr_t));
4277                         ARCSTAT_INCR(arcstat_l2_size, -ab->b_size);
4278                 }
4279 
4280                 /*
4281                  * Allow ARC to begin reads to this L2ARC entry.
4282                  */
4283                 ab->b_flags &= ~ARC_L2_WRITING;
4284 
4285                 mutex_exit(hash_lock);
4286         }
4287 
4288         atomic_inc_64(&l2arc_writes_done);
4289         list_remove(buflist, head);
4290         kmem_cache_free(hdr_cache, head);
4291         mutex_exit(&l2arc_buflist_mtx);
4292 
4293         vdev_space_update(dev->l2ad_vdev, -bytes_dropped, 0, 0);
4294 
4295         l2arc_do_free_on_write();
4296 
4297         kmem_free(cb, sizeof (l2arc_write_callback_t));
4298 }
4299 
4300 /*
4301  * A read to a cache device completed.  Validate buffer contents before
4302  * handing over to the regular ARC routines.
4303  */
4304 static void
4305 l2arc_read_done(zio_t *zio)
4306 {
4307         l2arc_read_callback_t *cb;
4308         arc_buf_hdr_t *hdr;
4309         arc_buf_t *buf;
4310         kmutex_t *hash_lock;
4311         int equal;
4312 
4313         ASSERT(zio->io_vd != NULL);
4314         ASSERT(zio->io_flags & ZIO_FLAG_DONT_PROPAGATE);
4315 
4316         spa_config_exit(zio->io_spa, SCL_L2ARC, zio->io_vd);
4317 
4318         cb = zio->io_private;
4319         ASSERT(cb != NULL);
4320         buf = cb->l2rcb_buf;
4321         ASSERT(buf != NULL);
4322 
4323         hash_lock = HDR_LOCK(buf->b_hdr);
4324         mutex_enter(hash_lock);
4325         hdr = buf->b_hdr;
4326         ASSERT3P(hash_lock, ==, HDR_LOCK(hdr));
4327 
4328         /*
4329          * If the buffer was compressed, decompress it first.
4330          */
4331         if (cb->l2rcb_compress != ZIO_COMPRESS_OFF)
4332                 l2arc_decompress_zio(zio, hdr, cb->l2rcb_compress);
4333         ASSERT(zio->io_data != NULL);
4334 
4335         /*
4336          * Check this survived the L2ARC journey.
4337          */
4338         equal = arc_cksum_equal(buf);
4339         if (equal && zio->io_error == 0 && !HDR_L2_EVICTED(hdr)) {
4340                 mutex_exit(hash_lock);
4341                 zio->io_private = buf;
4342                 zio->io_bp_copy = cb->l2rcb_bp;   /* XXX fix in L2ARC 2.0 */
4343                 zio->io_bp = &zio->io_bp_copy;        /* XXX fix in L2ARC 2.0 */
4344                 arc_read_done(zio);
4345         } else {
4346                 mutex_exit(hash_lock);
4347                 /*
4348                  * Buffer didn't survive caching.  Increment stats and
4349                  * reissue to the original storage device.
4350                  */
4351                 if (zio->io_error != 0) {
4352                         ARCSTAT_BUMP(arcstat_l2_io_error);
4353                 } else {
4354                         zio->io_error = SET_ERROR(EIO);
4355                 }
4356                 if (!equal)
4357                         ARCSTAT_BUMP(arcstat_l2_cksum_bad);
4358 
4359                 /*
4360                  * If there's no waiter, issue an async i/o to the primary
4361                  * storage now.  If there *is* a waiter, the caller must
4362                  * issue the i/o in a context where it's OK to block.
4363                  */
4364                 if (zio->io_waiter == NULL) {
4365                         zio_t *pio = zio_unique_parent(zio);
4366 
4367                         ASSERT(!pio || pio->io_child_type == ZIO_CHILD_LOGICAL);
4368 
4369                         zio_nowait(zio_read(pio, cb->l2rcb_spa, &cb->l2rcb_bp,
4370                             buf->b_data, zio->io_size, arc_read_done, buf,
4371                             zio->io_priority, cb->l2rcb_flags, &cb->l2rcb_zb));
4372                 }
4373         }
4374 
4375         kmem_free(cb, sizeof (l2arc_read_callback_t));
4376 }
4377 
4378 /*
4379  * This is the list priority from which the L2ARC will search for pages to
4380  * cache.  This is used within loops (0..3) to cycle through lists in the
4381  * desired order.  This order can have a significant effect on cache
4382  * performance.
4383  *
4384  * Currently the metadata lists are hit first, MFU then MRU, followed by
4385  * the data lists.  This function returns a locked list, and also returns
4386  * the lock pointer.
4387  */
4388 static list_t *
4389 l2arc_list_locked(int list_num, kmutex_t **lock)
4390 {
4391         list_t *list = NULL;
4392 
4393         ASSERT(list_num >= 0 && list_num <= 3);
4394 
4395         switch (list_num) {
4396         case 0:
4397                 list = &arc_mfu->arcs_list[ARC_BUFC_METADATA];
4398                 *lock = &arc_mfu->arcs_mtx;
4399                 break;
4400         case 1:
4401                 list = &arc_mru->arcs_list[ARC_BUFC_METADATA];
4402                 *lock = &arc_mru->arcs_mtx;
4403                 break;
4404         case 2:
4405                 list = &arc_mfu->arcs_list[ARC_BUFC_DATA];
4406                 *lock = &arc_mfu->arcs_mtx;
4407                 break;
4408         case 3:
4409                 list = &arc_mru->arcs_list[ARC_BUFC_DATA];
4410                 *lock = &arc_mru->arcs_mtx;
4411                 break;
4412         }
4413 
4414         ASSERT(!(MUTEX_HELD(*lock)));
4415         mutex_enter(*lock);
4416         return (list);
4417 }
4418 
4419 /*
4420  * Evict buffers from the device write hand to the distance specified in
4421  * bytes.  This distance may span populated buffers, it may span nothing.
4422  * This is clearing a region on the L2ARC device ready for writing.
4423  * If the 'all' boolean is set, every buffer is evicted.
4424  */
4425 static void
4426 l2arc_evict(l2arc_dev_t *dev, uint64_t distance, boolean_t all)
4427 {
4428         list_t *buflist;
4429         l2arc_buf_hdr_t *abl2;
4430         arc_buf_hdr_t *ab, *ab_prev;
4431         kmutex_t *hash_lock;
4432         uint64_t taddr;
4433         int64_t bytes_evicted = 0;
4434 
4435         buflist = dev->l2ad_buflist;
4436 
4437         if (buflist == NULL)
4438                 return;
4439 
4440         if (!all && dev->l2ad_first) {
4441                 /*
4442                  * This is the first sweep through the device.  There is
4443                  * nothing to evict.
4444                  */
4445                 return;
4446         }
4447 
4448         if (dev->l2ad_hand >= (dev->l2ad_end - (2 * distance))) {
4449                 /*
4450                  * When nearing the end of the device, evict to the end
4451                  * before the device write hand jumps to the start.
4452                  */
4453                 taddr = dev->l2ad_end;
4454         } else {
4455                 taddr = dev->l2ad_hand + distance;
4456         }
4457         DTRACE_PROBE4(l2arc__evict, l2arc_dev_t *, dev, list_t *, buflist,
4458             uint64_t, taddr, boolean_t, all);
4459 
4460 top:
4461         mutex_enter(&l2arc_buflist_mtx);
4462         for (ab = list_tail(buflist); ab; ab = ab_prev) {
4463                 ab_prev = list_prev(buflist, ab);
4464 
4465                 hash_lock = HDR_LOCK(ab);
4466                 if (!mutex_tryenter(hash_lock)) {
4467                         /*
4468                          * Missed the hash lock.  Retry.
4469                          */
4470                         ARCSTAT_BUMP(arcstat_l2_evict_lock_retry);
4471                         mutex_exit(&l2arc_buflist_mtx);
4472                         mutex_enter(hash_lock);
4473                         mutex_exit(hash_lock);
4474                         goto top;
4475                 }
4476 
4477                 if (HDR_L2_WRITE_HEAD(ab)) {
4478                         /*
4479                          * We hit a write head node.  Leave it for
4480                          * l2arc_write_done().
4481                          */
4482                         list_remove(buflist, ab);
4483                         mutex_exit(hash_lock);
4484                         continue;
4485                 }
4486 
4487                 if (!all && ab->b_l2hdr != NULL &&
4488                     (ab->b_l2hdr->b_daddr > taddr ||
4489                     ab->b_l2hdr->b_daddr < dev->l2ad_hand)) {
4490                         /*
4491                          * We've evicted to the target address,
4492                          * or the end of the device.
4493                          */
4494                         mutex_exit(hash_lock);
4495                         break;
4496                 }
4497 
4498                 if (HDR_FREE_IN_PROGRESS(ab)) {
4499                         /*
4500                          * Already on the path to destruction.
4501                          */
4502                         mutex_exit(hash_lock);
4503                         continue;
4504                 }
4505 
4506                 if (ab->b_state == arc_l2c_only) {
4507                         ASSERT(!HDR_L2_READING(ab));
4508                         /*
4509                          * This doesn't exist in the ARC.  Destroy.
4510                          * arc_hdr_destroy() will call list_remove()
4511                          * and decrement arcstat_l2_size.
4512                          */
4513                         arc_change_state(arc_anon, ab, hash_lock);
4514                         arc_hdr_destroy(ab);
4515                 } else {
4516                         /*
4517                          * Invalidate issued or about to be issued
4518                          * reads, since we may be about to write
4519                          * over this location.
4520                          */
4521                         if (HDR_L2_READING(ab)) {
4522                                 ARCSTAT_BUMP(arcstat_l2_evict_reading);
4523                                 ab->b_flags |= ARC_L2_EVICTED;
4524                         }
4525 
4526                         /*
4527                          * Tell ARC this no longer exists in L2ARC.
4528                          */
4529                         if (ab->b_l2hdr != NULL) {
4530                                 abl2 = ab->b_l2hdr;
4531                                 ARCSTAT_INCR(arcstat_l2_asize, -abl2->b_asize);
4532                                 bytes_evicted += abl2->b_asize;
4533                                 ab->b_l2hdr = NULL;
4534                                 kmem_free(abl2, sizeof (l2arc_buf_hdr_t));
4535                                 ARCSTAT_INCR(arcstat_l2_size, -ab->b_size);
4536                         }
4537                         list_remove(buflist, ab);
4538 
4539                         /*
4540                          * This may have been leftover after a
4541                          * failed write.
4542                          */
4543                         ab->b_flags &= ~ARC_L2_WRITING;
4544                 }
4545                 mutex_exit(hash_lock);
4546         }
4547         mutex_exit(&l2arc_buflist_mtx);
4548 
4549         vdev_space_update(dev->l2ad_vdev, -bytes_evicted, 0, 0);
4550         dev->l2ad_evict = taddr;
4551 }
4552 
4553 /*
4554  * Find and write ARC buffers to the L2ARC device.
4555  *
4556  * An ARC_L2_WRITING flag is set so that the L2ARC buffers are not valid
4557  * for reading until they have completed writing.
4558  * The headroom_boost is an in-out parameter used to maintain headroom boost
4559  * state between calls to this function.
4560  *
4561  * Returns the number of bytes actually written (which may be smaller than
4562  * the delta by which the device hand has changed due to alignment).
4563  */
4564 static uint64_t
4565 l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz,
4566     boolean_t *headroom_boost)
4567 {
4568         arc_buf_hdr_t *ab, *ab_prev, *head;
4569         list_t *list;
4570         uint64_t write_asize, write_psize, write_sz, headroom,
4571             buf_compress_minsz;
4572         void *buf_data;
4573         kmutex_t *list_lock;
4574         boolean_t full;
4575         l2arc_write_callback_t *cb;
4576         zio_t *pio, *wzio;
4577         uint64_t guid = spa_load_guid(spa);
4578         const boolean_t do_headroom_boost = *headroom_boost;
4579 
4580         ASSERT(dev->l2ad_vdev != NULL);
4581 
4582         /* Lower the flag now, we might want to raise it again later. */
4583         *headroom_boost = B_FALSE;
4584 
4585         pio = NULL;
4586         write_sz = write_asize = write_psize = 0;
4587         full = B_FALSE;
4588         head = kmem_cache_alloc(hdr_cache, KM_PUSHPAGE);
4589         head->b_flags |= ARC_L2_WRITE_HEAD;
4590 
4591         /*
4592          * We will want to try to compress buffers that are at least 2x the
4593          * device sector size.
4594          */
4595         buf_compress_minsz = 2 << dev->l2ad_vdev->vdev_ashift;
4596 
4597         /*
4598          * Copy buffers for L2ARC writing.
4599          */
4600         mutex_enter(&l2arc_buflist_mtx);
4601         for (int try = 0; try <= 3; try++) {
4602                 uint64_t passed_sz = 0;
4603 
4604                 list = l2arc_list_locked(try, &list_lock);
4605 
4606                 /*
4607                  * L2ARC fast warmup.
4608                  *
4609                  * Until the ARC is warm and starts to evict, read from the
4610                  * head of the ARC lists rather than the tail.
4611                  */
4612                 if (arc_warm == B_FALSE)
4613                         ab = list_head(list);
4614                 else
4615                         ab = list_tail(list);
4616 
4617                 headroom = target_sz * l2arc_headroom;
4618                 if (do_headroom_boost)
4619                         headroom = (headroom * l2arc_headroom_boost) / 100;
4620 
4621                 for (; ab; ab = ab_prev) {
4622                         l2arc_buf_hdr_t *l2hdr;
4623                         kmutex_t *hash_lock;
4624                         uint64_t buf_sz;
4625 
4626                         if (arc_warm == B_FALSE)
4627                                 ab_prev = list_next(list, ab);
4628                         else
4629                                 ab_prev = list_prev(list, ab);
4630 
4631                         hash_lock = HDR_LOCK(ab);
4632                         if (!mutex_tryenter(hash_lock)) {
4633                                 /*
4634                                  * Skip this buffer rather than waiting.
4635                                  */
4636                                 continue;
4637                         }
4638 
4639                         passed_sz += ab->b_size;
4640                         if (passed_sz > headroom) {
4641                                 /*
4642                                  * Searched too far.
4643                                  */
4644                                 mutex_exit(hash_lock);
4645                                 break;
4646                         }
4647 
4648                         if (!l2arc_write_eligible(guid, ab)) {
4649                                 mutex_exit(hash_lock);
4650                                 continue;
4651                         }
4652 
4653                         if ((write_sz + ab->b_size) > target_sz) {
4654                                 full = B_TRUE;
4655                                 mutex_exit(hash_lock);
4656                                 break;
4657                         }
4658 
4659                         if (pio == NULL) {
4660                                 /*
4661                                  * Insert a dummy header on the buflist so
4662                                  * l2arc_write_done() can find where the
4663                                  * write buffers begin without searching.
4664                                  */
4665                                 list_insert_head(dev->l2ad_buflist, head);
4666 
4667                                 cb = kmem_alloc(
4668                                     sizeof (l2arc_write_callback_t), KM_SLEEP);
4669                                 cb->l2wcb_dev = dev;
4670                                 cb->l2wcb_head = head;
4671                                 pio = zio_root(spa, l2arc_write_done, cb,
4672                                     ZIO_FLAG_CANFAIL);
4673                         }
4674 
4675                         /*
4676                          * Create and add a new L2ARC header.
4677                          */
4678                         l2hdr = kmem_zalloc(sizeof (l2arc_buf_hdr_t), KM_SLEEP);
4679                         l2hdr->b_dev = dev;
4680                         ab->b_flags |= ARC_L2_WRITING;
4681 
4682                         /*
4683                          * Temporarily stash the data buffer in b_tmp_cdata.
4684                          * The subsequent write step will pick it up from
4685                          * there. This is because can't access ab->b_buf
4686                          * without holding the hash_lock, which we in turn
4687                          * can't access without holding the ARC list locks
4688                          * (which we want to avoid during compression/writing).
4689                          */
4690                         l2hdr->b_compress = ZIO_COMPRESS_OFF;
4691                         l2hdr->b_asize = ab->b_size;
4692                         l2hdr->b_tmp_cdata = ab->b_buf->b_data;
4693 
4694                         buf_sz = ab->b_size;
4695                         ab->b_l2hdr = l2hdr;
4696 
4697                         list_insert_head(dev->l2ad_buflist, ab);
4698 
4699                         /*
4700                          * Compute and store the buffer cksum before
4701                          * writing.  On debug the cksum is verified first.
4702                          */
4703                         arc_cksum_verify(ab->b_buf);
4704                         arc_cksum_compute(ab->b_buf, B_TRUE);
4705 
4706                         mutex_exit(hash_lock);
4707 
4708                         write_sz += buf_sz;
4709                 }
4710 
4711                 mutex_exit(list_lock);
4712 
4713                 if (full == B_TRUE)
4714                         break;
4715         }
4716 
4717         /* No buffers selected for writing? */
4718         if (pio == NULL) {
4719                 ASSERT0(write_sz);
4720                 mutex_exit(&l2arc_buflist_mtx);
4721                 kmem_cache_free(hdr_cache, head);
4722                 return (0);
4723         }
4724 
4725         /*
4726          * Now start writing the buffers. We're starting at the write head
4727          * and work backwards, retracing the course of the buffer selector
4728          * loop above.
4729          */
4730         for (ab = list_prev(dev->l2ad_buflist, head); ab;
4731             ab = list_prev(dev->l2ad_buflist, ab)) {
4732                 l2arc_buf_hdr_t *l2hdr;
4733                 uint64_t buf_sz;
4734 
4735                 /*
4736                  * We shouldn't need to lock the buffer here, since we flagged
4737                  * it as ARC_L2_WRITING in the previous step, but we must take
4738                  * care to only access its L2 cache parameters. In particular,
4739                  * ab->b_buf may be invalid by now due to ARC eviction.
4740                  */
4741                 l2hdr = ab->b_l2hdr;
4742                 l2hdr->b_daddr = dev->l2ad_hand;
4743 
4744                 if ((ab->b_flags & ARC_L2COMPRESS) &&
4745                     l2hdr->b_asize >= buf_compress_minsz) {
4746                         if (l2arc_compress_buf(l2hdr)) {
4747                                 /*
4748                                  * If compression succeeded, enable headroom
4749                                  * boost on the next scan cycle.
4750                                  */
4751                                 *headroom_boost = B_TRUE;
4752                         }
4753                 }
4754 
4755                 /*
4756                  * Pick up the buffer data we had previously stashed away
4757                  * (and now potentially also compressed).
4758                  */
4759                 buf_data = l2hdr->b_tmp_cdata;
4760                 buf_sz = l2hdr->b_asize;
4761 
4762                 /* Compression may have squashed the buffer to zero length. */
4763                 if (buf_sz != 0) {
4764                         uint64_t buf_p_sz;
4765 
4766                         wzio = zio_write_phys(pio, dev->l2ad_vdev,
4767                             dev->l2ad_hand, buf_sz, buf_data, ZIO_CHECKSUM_OFF,
4768                             NULL, NULL, ZIO_PRIORITY_ASYNC_WRITE,
4769                             ZIO_FLAG_CANFAIL, B_FALSE);
4770 
4771                         DTRACE_PROBE2(l2arc__write, vdev_t *, dev->l2ad_vdev,
4772                             zio_t *, wzio);
4773                         (void) zio_nowait(wzio);
4774 
4775                         write_asize += buf_sz;
4776                         /*
4777                          * Keep the clock hand suitably device-aligned.
4778                          */
4779                         buf_p_sz = vdev_psize_to_asize(dev->l2ad_vdev, buf_sz);
4780                         write_psize += buf_p_sz;
4781                         dev->l2ad_hand += buf_p_sz;
4782                 }
4783         }
4784 
4785         mutex_exit(&l2arc_buflist_mtx);
4786 
4787         ASSERT3U(write_asize, <=, target_sz);
4788         ARCSTAT_BUMP(arcstat_l2_writes_sent);
4789         ARCSTAT_INCR(arcstat_l2_write_bytes, write_asize);
4790         ARCSTAT_INCR(arcstat_l2_size, write_sz);
4791         ARCSTAT_INCR(arcstat_l2_asize, write_asize);
4792         vdev_space_update(dev->l2ad_vdev, write_asize, 0, 0);
4793 
4794         /*
4795          * Bump device hand to the device start if it is approaching the end.
4796          * l2arc_evict() will already have evicted ahead for this case.
4797          */
4798         if (dev->l2ad_hand >= (dev->l2ad_end - target_sz)) {
4799                 dev->l2ad_hand = dev->l2ad_start;
4800                 dev->l2ad_evict = dev->l2ad_start;
4801                 dev->l2ad_first = B_FALSE;
4802         }
4803 
4804         dev->l2ad_writing = B_TRUE;
4805         (void) zio_wait(pio);
4806         dev->l2ad_writing = B_FALSE;
4807 
4808         return (write_asize);
4809 }
4810 
4811 /*
4812  * Compresses an L2ARC buffer.
4813  * The data to be compressed must be prefilled in l2hdr->b_tmp_cdata and its
4814  * size in l2hdr->b_asize. This routine tries to compress the data and
4815  * depending on the compression result there are three possible outcomes:
4816  * *) The buffer was incompressible. The original l2hdr contents were left
4817  *    untouched and are ready for writing to an L2 device.
4818  * *) The buffer was all-zeros, so there is no need to write it to an L2
4819  *    device. To indicate this situation b_tmp_cdata is NULL'ed, b_asize is
4820  *    set to zero and b_compress is set to ZIO_COMPRESS_EMPTY.
4821  * *) Compression succeeded and b_tmp_cdata was replaced with a temporary
4822  *    data buffer which holds the compressed data to be written, and b_asize
4823  *    tells us how much data there is. b_compress is set to the appropriate
4824  *    compression algorithm. Once writing is done, invoke
4825  *    l2arc_release_cdata_buf on this l2hdr to free this temporary buffer.
4826  *
4827  * Returns B_TRUE if compression succeeded, or B_FALSE if it didn't (the
4828  * buffer was incompressible).
4829  */
4830 static boolean_t
4831 l2arc_compress_buf(l2arc_buf_hdr_t *l2hdr)
4832 {
4833         void *cdata;
4834         size_t csize, len, rounded;
4835 
4836         ASSERT(l2hdr->b_compress == ZIO_COMPRESS_OFF);
4837         ASSERT(l2hdr->b_tmp_cdata != NULL);
4838 
4839         len = l2hdr->b_asize;
4840         cdata = zio_data_buf_alloc(len);
4841         csize = zio_compress_data(ZIO_COMPRESS_LZ4, l2hdr->b_tmp_cdata,
4842             cdata, l2hdr->b_asize);
4843 
4844         rounded = P2ROUNDUP(csize, (size_t)SPA_MINBLOCKSIZE);
4845         if (rounded > csize) {
4846                 bzero((char *)cdata + csize, rounded - csize);
4847                 csize = rounded;
4848         }
4849 
4850         if (csize == 0) {
4851                 /* zero block, indicate that there's nothing to write */
4852                 zio_data_buf_free(cdata, len);
4853                 l2hdr->b_compress = ZIO_COMPRESS_EMPTY;
4854                 l2hdr->b_asize = 0;
4855                 l2hdr->b_tmp_cdata = NULL;
4856                 ARCSTAT_BUMP(arcstat_l2_compress_zeros);
4857                 return (B_TRUE);
4858         } else if (csize > 0 && csize < len) {
4859                 /*
4860                  * Compression succeeded, we'll keep the cdata around for
4861                  * writing and release it afterwards.
4862                  */
4863                 l2hdr->b_compress = ZIO_COMPRESS_LZ4;
4864                 l2hdr->b_asize = csize;
4865                 l2hdr->b_tmp_cdata = cdata;
4866                 ARCSTAT_BUMP(arcstat_l2_compress_successes);
4867                 return (B_TRUE);
4868         } else {
4869                 /*
4870                  * Compression failed, release the compressed buffer.
4871                  * l2hdr will be left unmodified.
4872                  */
4873                 zio_data_buf_free(cdata, len);
4874                 ARCSTAT_BUMP(arcstat_l2_compress_failures);
4875                 return (B_FALSE);
4876         }
4877 }
4878 
4879 /*
4880  * Decompresses a zio read back from an l2arc device. On success, the
4881  * underlying zio's io_data buffer is overwritten by the uncompressed
4882  * version. On decompression error (corrupt compressed stream), the
4883  * zio->io_error value is set to signal an I/O error.
4884  *
4885  * Please note that the compressed data stream is not checksummed, so
4886  * if the underlying device is experiencing data corruption, we may feed
4887  * corrupt data to the decompressor, so the decompressor needs to be
4888  * able to handle this situation (LZ4 does).
4889  */
4890 static void
4891 l2arc_decompress_zio(zio_t *zio, arc_buf_hdr_t *hdr, enum zio_compress c)
4892 {
4893         ASSERT(L2ARC_IS_VALID_COMPRESS(c));
4894 
4895         if (zio->io_error != 0) {
4896                 /*
4897                  * An io error has occured, just restore the original io
4898                  * size in preparation for a main pool read.
4899                  */
4900                 zio->io_orig_size = zio->io_size = hdr->b_size;
4901                 return;
4902         }
4903 
4904         if (c == ZIO_COMPRESS_EMPTY) {
4905                 /*
4906                  * An empty buffer results in a null zio, which means we
4907                  * need to fill its io_data after we're done restoring the
4908                  * buffer's contents.
4909                  */
4910                 ASSERT(hdr->b_buf != NULL);
4911                 bzero(hdr->b_buf->b_data, hdr->b_size);
4912                 zio->io_data = zio->io_orig_data = hdr->b_buf->b_data;
4913         } else {
4914                 ASSERT(zio->io_data != NULL);
4915                 /*
4916                  * We copy the compressed data from the start of the arc buffer
4917                  * (the zio_read will have pulled in only what we need, the
4918                  * rest is garbage which we will overwrite at decompression)
4919                  * and then decompress back to the ARC data buffer. This way we
4920                  * can minimize copying by simply decompressing back over the
4921                  * original compressed data (rather than decompressing to an
4922                  * aux buffer and then copying back the uncompressed buffer,
4923                  * which is likely to be much larger).
4924                  */
4925                 uint64_t csize;
4926                 void *cdata;
4927 
4928                 csize = zio->io_size;
4929                 cdata = zio_data_buf_alloc(csize);
4930                 bcopy(zio->io_data, cdata, csize);
4931                 if (zio_decompress_data(c, cdata, zio->io_data, csize,
4932                     hdr->b_size) != 0)
4933                         zio->io_error = EIO;
4934                 zio_data_buf_free(cdata, csize);
4935         }
4936 
4937         /* Restore the expected uncompressed IO size. */
4938         zio->io_orig_size = zio->io_size = hdr->b_size;
4939 }
4940 
4941 /*
4942  * Releases the temporary b_tmp_cdata buffer in an l2arc header structure.
4943  * This buffer serves as a temporary holder of compressed data while
4944  * the buffer entry is being written to an l2arc device. Once that is
4945  * done, we can dispose of it.
4946  */
4947 static void
4948 l2arc_release_cdata_buf(arc_buf_hdr_t *ab)
4949 {
4950         l2arc_buf_hdr_t *l2hdr = ab->b_l2hdr;
4951 
4952         if (l2hdr->b_compress == ZIO_COMPRESS_LZ4) {
4953                 /*
4954                  * If the data was compressed, then we've allocated a
4955                  * temporary buffer for it, so now we need to release it.
4956                  */
4957                 ASSERT(l2hdr->b_tmp_cdata != NULL);
4958                 zio_data_buf_free(l2hdr->b_tmp_cdata, ab->b_size);
4959         }
4960         l2hdr->b_tmp_cdata = NULL;
4961 }
4962 
4963 /*
4964  * This thread feeds the L2ARC at regular intervals.  This is the beating
4965  * heart of the L2ARC.
4966  */
4967 static void
4968 l2arc_feed_thread(void)
4969 {
4970         callb_cpr_t cpr;
4971         l2arc_dev_t *dev;
4972         spa_t *spa;
4973         uint64_t size, wrote;
4974         clock_t begin, next = ddi_get_lbolt();
4975         boolean_t headroom_boost = B_FALSE;
4976 
4977         CALLB_CPR_INIT(&cpr, &l2arc_feed_thr_lock, callb_generic_cpr, FTAG);
4978 
4979         mutex_enter(&l2arc_feed_thr_lock);
4980 
4981         while (l2arc_thread_exit == 0) {
4982                 CALLB_CPR_SAFE_BEGIN(&cpr);
4983                 (void) cv_timedwait(&l2arc_feed_thr_cv, &l2arc_feed_thr_lock,
4984                     next);
4985                 CALLB_CPR_SAFE_END(&cpr, &l2arc_feed_thr_lock);
4986                 next = ddi_get_lbolt() + hz;
4987 
4988                 /*
4989                  * Quick check for L2ARC devices.
4990                  */
4991                 mutex_enter(&l2arc_dev_mtx);
4992                 if (l2arc_ndev == 0) {
4993                         mutex_exit(&l2arc_dev_mtx);
4994                         continue;
4995                 }
4996                 mutex_exit(&l2arc_dev_mtx);
4997                 begin = ddi_get_lbolt();
4998 
4999                 /*
5000                  * This selects the next l2arc device to write to, and in
5001                  * doing so the next spa to feed from: dev->l2ad_spa.   This
5002                  * will return NULL if there are now no l2arc devices or if
5003                  * they are all faulted.
5004                  *
5005                  * If a device is returned, its spa's config lock is also
5006                  * held to prevent device removal.  l2arc_dev_get_next()
5007                  * will grab and release l2arc_dev_mtx.
5008                  */
5009                 if ((dev = l2arc_dev_get_next()) == NULL)
5010                         continue;
5011 
5012                 spa = dev->l2ad_spa;
5013                 ASSERT(spa != NULL);
5014 
5015                 /*
5016                  * If the pool is read-only then force the feed thread to
5017                  * sleep a little longer.
5018                  */
5019                 if (!spa_writeable(spa)) {
5020                         next = ddi_get_lbolt() + 5 * l2arc_feed_secs * hz;
5021                         spa_config_exit(spa, SCL_L2ARC, dev);
5022                         continue;
5023                 }
5024 
5025                 /*
5026                  * Avoid contributing to memory pressure.
5027                  */
5028                 if (arc_reclaim_needed()) {
5029                         ARCSTAT_BUMP(arcstat_l2_abort_lowmem);
5030                         spa_config_exit(spa, SCL_L2ARC, dev);
5031                         continue;
5032                 }
5033 
5034                 ARCSTAT_BUMP(arcstat_l2_feeds);
5035 
5036                 size = l2arc_write_size();
5037 
5038                 /*
5039                  * Evict L2ARC buffers that will be overwritten.
5040                  */
5041                 l2arc_evict(dev, size, B_FALSE);
5042 
5043                 /*
5044                  * Write ARC buffers.
5045                  */
5046                 wrote = l2arc_write_buffers(spa, dev, size, &headroom_boost);
5047 
5048                 /*
5049                  * Calculate interval between writes.
5050                  */
5051                 next = l2arc_write_interval(begin, size, wrote);
5052                 spa_config_exit(spa, SCL_L2ARC, dev);
5053         }
5054 
5055         l2arc_thread_exit = 0;
5056         cv_broadcast(&l2arc_feed_thr_cv);
5057         CALLB_CPR_EXIT(&cpr);               /* drops l2arc_feed_thr_lock */
5058         thread_exit();
5059 }
5060 
5061 boolean_t
5062 l2arc_vdev_present(vdev_t *vd)
5063 {
5064         l2arc_dev_t *dev;
5065 
5066         mutex_enter(&l2arc_dev_mtx);
5067         for (dev = list_head(l2arc_dev_list); dev != NULL;
5068             dev = list_next(l2arc_dev_list, dev)) {
5069                 if (dev->l2ad_vdev == vd)
5070                         break;
5071         }
5072         mutex_exit(&l2arc_dev_mtx);
5073 
5074         return (dev != NULL);
5075 }
5076 
5077 /*
5078  * Add a vdev for use by the L2ARC.  By this point the spa has already
5079  * validated the vdev and opened it.
5080  */
5081 void
5082 l2arc_add_vdev(spa_t *spa, vdev_t *vd)
5083 {
5084         l2arc_dev_t *adddev;
5085 
5086         ASSERT(!l2arc_vdev_present(vd));
5087 
5088         /*
5089          * Create a new l2arc device entry.
5090          */
5091         adddev = kmem_zalloc(sizeof (l2arc_dev_t), KM_SLEEP);
5092         adddev->l2ad_spa = spa;
5093         adddev->l2ad_vdev = vd;
5094         adddev->l2ad_start = VDEV_LABEL_START_SIZE;
5095         adddev->l2ad_end = VDEV_LABEL_START_SIZE + vdev_get_min_asize(vd);
5096         adddev->l2ad_hand = adddev->l2ad_start;
5097         adddev->l2ad_evict = adddev->l2ad_start;
5098         adddev->l2ad_first = B_TRUE;
5099         adddev->l2ad_writing = B_FALSE;
5100 
5101         /*
5102          * This is a list of all ARC buffers that are still valid on the
5103          * device.
5104          */
5105         adddev->l2ad_buflist = kmem_zalloc(sizeof (list_t), KM_SLEEP);
5106         list_create(adddev->l2ad_buflist, sizeof (arc_buf_hdr_t),
5107             offsetof(arc_buf_hdr_t, b_l2node));
5108 
5109         vdev_space_update(vd, 0, 0, adddev->l2ad_end - adddev->l2ad_hand);
5110 
5111         /*
5112          * Add device to global list
5113          */
5114         mutex_enter(&l2arc_dev_mtx);
5115         list_insert_head(l2arc_dev_list, adddev);
5116         atomic_inc_64(&l2arc_ndev);
5117         mutex_exit(&l2arc_dev_mtx);
5118 }
5119 
5120 /*
5121  * Remove a vdev from the L2ARC.
5122  */
5123 void
5124 l2arc_remove_vdev(vdev_t *vd)
5125 {
5126         l2arc_dev_t *dev, *nextdev, *remdev = NULL;
5127 
5128         /*
5129          * Find the device by vdev
5130          */
5131         mutex_enter(&l2arc_dev_mtx);
5132         for (dev = list_head(l2arc_dev_list); dev; dev = nextdev) {
5133                 nextdev = list_next(l2arc_dev_list, dev);
5134                 if (vd == dev->l2ad_vdev) {
5135                         remdev = dev;
5136                         break;
5137                 }
5138         }
5139         ASSERT(remdev != NULL);
5140 
5141         /*
5142          * Remove device from global list
5143          */
5144         list_remove(l2arc_dev_list, remdev);
5145         l2arc_dev_last = NULL;          /* may have been invalidated */
5146         atomic_dec_64(&l2arc_ndev);
5147         mutex_exit(&l2arc_dev_mtx);
5148 
5149         /*
5150          * Clear all buflists and ARC references.  L2ARC device flush.
5151          */
5152         l2arc_evict(remdev, 0, B_TRUE);
5153         list_destroy(remdev->l2ad_buflist);
5154         kmem_free(remdev->l2ad_buflist, sizeof (list_t));
5155         kmem_free(remdev, sizeof (l2arc_dev_t));
5156 }
5157 
5158 void
5159 l2arc_init(void)
5160 {
5161         l2arc_thread_exit = 0;
5162         l2arc_ndev = 0;
5163         l2arc_writes_sent = 0;
5164         l2arc_writes_done = 0;
5165 
5166         mutex_init(&l2arc_feed_thr_lock, NULL, MUTEX_DEFAULT, NULL);
5167         cv_init(&l2arc_feed_thr_cv, NULL, CV_DEFAULT, NULL);
5168         mutex_init(&l2arc_dev_mtx, NULL, MUTEX_DEFAULT, NULL);
5169         mutex_init(&l2arc_buflist_mtx, NULL, MUTEX_DEFAULT, NULL);
5170         mutex_init(&l2arc_free_on_write_mtx, NULL, MUTEX_DEFAULT, NULL);
5171 
5172         l2arc_dev_list = &L2ARC_dev_list;
5173         l2arc_free_on_write = &L2ARC_free_on_write;
5174         list_create(l2arc_dev_list, sizeof (l2arc_dev_t),
5175             offsetof(l2arc_dev_t, l2ad_node));
5176         list_create(l2arc_free_on_write, sizeof (l2arc_data_free_t),
5177             offsetof(l2arc_data_free_t, l2df_list_node));
5178 }
5179 
5180 void
5181 l2arc_fini(void)
5182 {
5183         /*
5184          * This is called from dmu_fini(), which is called from spa_fini();
5185          * Because of this, we can assume that all l2arc devices have
5186          * already been removed when the pools themselves were removed.
5187          */
5188 
5189         l2arc_do_free_on_write();
5190 
5191         mutex_destroy(&l2arc_feed_thr_lock);
5192         cv_destroy(&l2arc_feed_thr_cv);
5193         mutex_destroy(&l2arc_dev_mtx);
5194         mutex_destroy(&l2arc_buflist_mtx);
5195         mutex_destroy(&l2arc_free_on_write_mtx);
5196 
5197         list_destroy(l2arc_dev_list);
5198         list_destroy(l2arc_free_on_write);
5199 }
5200 
5201 void
5202 l2arc_start(void)
5203 {
5204         if (!(spa_mode_global & FWRITE))
5205                 return;
5206 
5207         (void) thread_create(NULL, 0, l2arc_feed_thread, NULL, 0, &p0,
5208             TS_RUN, minclsyspri);
5209 }
5210 
5211 void
5212 l2arc_stop(void)
5213 {
5214         if (!(spa_mode_global & FWRITE))
5215                 return;
5216 
5217         mutex_enter(&l2arc_feed_thr_lock);
5218         cv_signal(&l2arc_feed_thr_cv);      /* kick thread out of startup */
5219         l2arc_thread_exit = 1;
5220         while (l2arc_thread_exit != 0)
5221                 cv_wait(&l2arc_feed_thr_cv, &l2arc_feed_thr_lock);
5222         mutex_exit(&l2arc_feed_thr_lock);
5223 }