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 2009 Sun Microsystems, Inc. All rights reserved.
23 * Use is subject to license terms.
24 */
25
26 #include <sys/zfs_context.h>
27 #include <sys/dnode.h>
28 #include <sys/dmu_objset.h>
29 #include <sys/dmu_zfetch.h>
30 #include <sys/dmu.h>
31 #include <sys/dbuf.h>
32 #include <sys/kstat.h>
33
34 /*
35 * I'm against tune-ables, but these should probably exist as tweakable globals
36 * until we can get this working the way we want it to.
37 */
38
39 int zfs_prefetch_disable = 0;
40
41 /* max # of streams per zfetch */
42 uint32_t zfetch_max_streams = 8;
43 /* min time before stream reclaim */
44 uint32_t zfetch_min_sec_reap = 2;
45 /* max number of blocks to fetch at a time */
46 uint32_t zfetch_block_cap = 256;
47 /* number of bytes in a array_read at which we stop prefetching (1Mb) */
48 uint64_t zfetch_array_rd_sz = 1024 * 1024;
49
50 /* forward decls for static routines */
51 static boolean_t dmu_zfetch_colinear(zfetch_t *, zstream_t *);
52 static void dmu_zfetch_dofetch(zfetch_t *, zstream_t *);
53 static uint64_t dmu_zfetch_fetch(dnode_t *, uint64_t, uint64_t);
54 static uint64_t dmu_zfetch_fetchsz(dnode_t *, uint64_t, uint64_t);
55 static boolean_t dmu_zfetch_find(zfetch_t *, zstream_t *, int);
56 static int dmu_zfetch_stream_insert(zfetch_t *, zstream_t *);
57 static zstream_t *dmu_zfetch_stream_reclaim(zfetch_t *);
58 static void dmu_zfetch_stream_remove(zfetch_t *, zstream_t *);
59 static int dmu_zfetch_streams_equal(zstream_t *, zstream_t *);
60
61 typedef struct zfetch_stats {
62 kstat_named_t zfetchstat_hits;
63 kstat_named_t zfetchstat_misses;
64 kstat_named_t zfetchstat_colinear_hits;
65 kstat_named_t zfetchstat_colinear_misses;
66 kstat_named_t zfetchstat_stride_hits;
67 kstat_named_t zfetchstat_stride_misses;
68 kstat_named_t zfetchstat_reclaim_successes;
69 kstat_named_t zfetchstat_reclaim_failures;
70 kstat_named_t zfetchstat_stream_resets;
71 kstat_named_t zfetchstat_stream_noresets;
72 kstat_named_t zfetchstat_bogus_streams;
73 } zfetch_stats_t;
74
75 static zfetch_stats_t zfetch_stats = {
76 { "hits", KSTAT_DATA_UINT64 },
77 { "misses", KSTAT_DATA_UINT64 },
78 { "colinear_hits", KSTAT_DATA_UINT64 },
79 { "colinear_misses", KSTAT_DATA_UINT64 },
80 { "stride_hits", KSTAT_DATA_UINT64 },
81 { "stride_misses", KSTAT_DATA_UINT64 },
82 { "reclaim_successes", KSTAT_DATA_UINT64 },
83 { "reclaim_failures", KSTAT_DATA_UINT64 },
84 { "streams_resets", KSTAT_DATA_UINT64 },
85 { "streams_noresets", KSTAT_DATA_UINT64 },
86 { "bogus_streams", KSTAT_DATA_UINT64 },
87 };
88
89 #define ZFETCHSTAT_INCR(stat, val) \
90 atomic_add_64(&zfetch_stats.stat.value.ui64, (val));
91
92 #define ZFETCHSTAT_BUMP(stat) ZFETCHSTAT_INCR(stat, 1);
93
94 kstat_t *zfetch_ksp;
95
96 /*
97 * Given a zfetch structure and a zstream structure, determine whether the
98 * blocks to be read are part of a co-linear pair of existing prefetch
99 * streams. If a set is found, coalesce the streams, removing one, and
100 * configure the prefetch so it looks for a strided access pattern.
101 *
102 * In other words: if we find two sequential access streams that are
103 * the same length and distance N appart, and this read is N from the
104 * last stream, then we are probably in a strided access pattern. So
105 * combine the two sequential streams into a single strided stream.
106 *
107 * Returns whether co-linear streams were found.
108 */
109 static boolean_t
110 dmu_zfetch_colinear(zfetch_t *zf, zstream_t *zh)
111 {
112 zstream_t *z_walk;
113 zstream_t *z_comp;
114
115 if (! rw_tryenter(&zf->zf_rwlock, RW_WRITER))
116 return (0);
117
118 if (zh == NULL) {
119 rw_exit(&zf->zf_rwlock);
120 return (0);
121 }
122
123 for (z_walk = list_head(&zf->zf_stream); z_walk;
124 z_walk = list_next(&zf->zf_stream, z_walk)) {
125 for (z_comp = list_next(&zf->zf_stream, z_walk); z_comp;
126 z_comp = list_next(&zf->zf_stream, z_comp)) {
127 int64_t diff;
128
129 if (z_walk->zst_len != z_walk->zst_stride ||
130 z_comp->zst_len != z_comp->zst_stride) {
131 continue;
132 }
133
134 diff = z_comp->zst_offset - z_walk->zst_offset;
135 if (z_comp->zst_offset + diff == zh->zst_offset) {
136 z_walk->zst_offset = zh->zst_offset;
137 z_walk->zst_direction = diff < 0 ? -1 : 1;
138 z_walk->zst_stride =
139 diff * z_walk->zst_direction;
140 z_walk->zst_ph_offset =
141 zh->zst_offset + z_walk->zst_stride;
142 dmu_zfetch_stream_remove(zf, z_comp);
143 mutex_destroy(&z_comp->zst_lock);
144 kmem_free(z_comp, sizeof (zstream_t));
145
146 dmu_zfetch_dofetch(zf, z_walk);
147
148 rw_exit(&zf->zf_rwlock);
149 return (1);
150 }
151
152 diff = z_walk->zst_offset - z_comp->zst_offset;
153 if (z_walk->zst_offset + diff == zh->zst_offset) {
154 z_walk->zst_offset = zh->zst_offset;
155 z_walk->zst_direction = diff < 0 ? -1 : 1;
156 z_walk->zst_stride =
157 diff * z_walk->zst_direction;
158 z_walk->zst_ph_offset =
159 zh->zst_offset + z_walk->zst_stride;
160 dmu_zfetch_stream_remove(zf, z_comp);
161 mutex_destroy(&z_comp->zst_lock);
162 kmem_free(z_comp, sizeof (zstream_t));
163
164 dmu_zfetch_dofetch(zf, z_walk);
165
166 rw_exit(&zf->zf_rwlock);
167 return (1);
168 }
169 }
170 }
171
172 rw_exit(&zf->zf_rwlock);
173 return (0);
174 }
175
176 /*
177 * Given a zstream_t, determine the bounds of the prefetch. Then call the
178 * routine that actually prefetches the individual blocks.
179 */
180 static void
181 dmu_zfetch_dofetch(zfetch_t *zf, zstream_t *zs)
182 {
183 uint64_t prefetch_tail;
184 uint64_t prefetch_limit;
185 uint64_t prefetch_ofst;
186 uint64_t prefetch_len;
187 uint64_t blocks_fetched;
188
189 zs->zst_stride = MAX((int64_t)zs->zst_stride, zs->zst_len);
190 zs->zst_cap = MIN(zfetch_block_cap, 2 * zs->zst_cap);
191
192 prefetch_tail = MAX((int64_t)zs->zst_ph_offset,
193 (int64_t)(zs->zst_offset + zs->zst_stride));
194 /*
195 * XXX: use a faster division method?
196 */
197 prefetch_limit = zs->zst_offset + zs->zst_len +
198 (zs->zst_cap * zs->zst_stride) / zs->zst_len;
199
200 while (prefetch_tail < prefetch_limit) {
201 prefetch_ofst = zs->zst_offset + zs->zst_direction *
202 (prefetch_tail - zs->zst_offset);
203
204 prefetch_len = zs->zst_len;
205
206 /*
207 * Don't prefetch beyond the end of the file, if working
208 * backwards.
209 */
210 if ((zs->zst_direction == ZFETCH_BACKWARD) &&
211 (prefetch_ofst > prefetch_tail)) {
212 prefetch_len += prefetch_ofst;
213 prefetch_ofst = 0;
214 }
215
216 /* don't prefetch more than we're supposed to */
217 if (prefetch_len > zs->zst_len)
218 break;
219
220 blocks_fetched = dmu_zfetch_fetch(zf->zf_dnode,
221 prefetch_ofst, zs->zst_len);
222
223 prefetch_tail += zs->zst_stride;
224 /* stop if we've run out of stuff to prefetch */
225 if (blocks_fetched < zs->zst_len)
226 break;
227 }
228 zs->zst_ph_offset = prefetch_tail;
229 zs->zst_last = ddi_get_lbolt();
230 }
231
232 void
233 zfetch_init(void)
234 {
235
236 zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc",
237 KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t),
238 KSTAT_FLAG_VIRTUAL);
239
240 if (zfetch_ksp != NULL) {
241 zfetch_ksp->ks_data = &zfetch_stats;
242 kstat_install(zfetch_ksp);
243 }
244 }
245
246 void
247 zfetch_fini(void)
248 {
249 if (zfetch_ksp != NULL) {
250 kstat_delete(zfetch_ksp);
251 zfetch_ksp = NULL;
252 }
253 }
254
255 /*
256 * This takes a pointer to a zfetch structure and a dnode. It performs the
257 * necessary setup for the zfetch structure, grokking data from the
258 * associated dnode.
259 */
260 void
261 dmu_zfetch_init(zfetch_t *zf, dnode_t *dno)
262 {
263 if (zf == NULL) {
264 return;
265 }
266
267 zf->zf_dnode = dno;
268 zf->zf_stream_cnt = 0;
269 zf->zf_alloc_fail = 0;
270
271 list_create(&zf->zf_stream, sizeof (zstream_t),
272 offsetof(zstream_t, zst_node));
273
274 rw_init(&zf->zf_rwlock, NULL, RW_DEFAULT, NULL);
275 }
276
277 /*
278 * This function computes the actual size, in blocks, that can be prefetched,
279 * and fetches it.
280 */
281 static uint64_t
282 dmu_zfetch_fetch(dnode_t *dn, uint64_t blkid, uint64_t nblks)
283 {
284 uint64_t fetchsz;
285 uint64_t i;
286
287 fetchsz = dmu_zfetch_fetchsz(dn, blkid, nblks);
288
289 for (i = 0; i < fetchsz; i++) {
290 dbuf_prefetch(dn, blkid + i);
291 }
292
293 return (fetchsz);
294 }
295
296 /*
297 * this function returns the number of blocks that would be prefetched, based
298 * upon the supplied dnode, blockid, and nblks. This is used so that we can
299 * update streams in place, and then prefetch with their old value after the
300 * fact. This way, we can delay the prefetch, but subsequent accesses to the
301 * stream won't result in the same data being prefetched multiple times.
302 */
303 static uint64_t
304 dmu_zfetch_fetchsz(dnode_t *dn, uint64_t blkid, uint64_t nblks)
305 {
306 uint64_t fetchsz;
307
308 if (blkid > dn->dn_maxblkid) {
309 return (0);
310 }
311
312 /* compute fetch size */
313 if (blkid + nblks + 1 > dn->dn_maxblkid) {
314 fetchsz = (dn->dn_maxblkid - blkid) + 1;
315 ASSERT(blkid + fetchsz - 1 <= dn->dn_maxblkid);
316 } else {
317 fetchsz = nblks;
318 }
319
320
321 return (fetchsz);
322 }
323
324 /*
325 * given a zfetch and a zstream structure, see if there is an associated zstream
326 * for this block read. If so, it starts a prefetch for the stream it
327 * located and returns true, otherwise it returns false
328 */
329 static boolean_t
330 dmu_zfetch_find(zfetch_t *zf, zstream_t *zh, int prefetched)
331 {
332 zstream_t *zs;
333 int64_t diff;
334 int reset = !prefetched;
335 int rc = 0;
336
337 if (zh == NULL)
338 return (0);
339
340 /*
341 * XXX: This locking strategy is a bit coarse; however, it's impact has
342 * yet to be tested. If this turns out to be an issue, it can be
343 * modified in a number of different ways.
344 */
345
346 rw_enter(&zf->zf_rwlock, RW_READER);
347 top:
348
349 for (zs = list_head(&zf->zf_stream); zs;
350 zs = list_next(&zf->zf_stream, zs)) {
351
352 /*
353 * XXX - should this be an assert?
354 */
355 if (zs->zst_len == 0) {
356 /* bogus stream */
357 ZFETCHSTAT_BUMP(zfetchstat_bogus_streams);
358 continue;
359 }
360
361 /*
362 * We hit this case when we are in a strided prefetch stream:
363 * we will read "len" blocks before "striding".
364 */
365 if (zh->zst_offset >= zs->zst_offset &&
366 zh->zst_offset < zs->zst_offset + zs->zst_len) {
367 if (prefetched) {
368 /* already fetched */
369 ZFETCHSTAT_BUMP(zfetchstat_stride_hits);
370 rc = 1;
371 goto out;
372 } else {
373 ZFETCHSTAT_BUMP(zfetchstat_stride_misses);
374 }
375 }
376
377 /*
378 * This is the forward sequential read case: we increment
379 * len by one each time we hit here, so we will enter this
380 * case on every read.
381 */
382 if (zh->zst_offset == zs->zst_offset + zs->zst_len) {
383
384 reset = !prefetched && zs->zst_len > 1;
385
386 mutex_enter(&zs->zst_lock);
387
388 if (zh->zst_offset != zs->zst_offset + zs->zst_len) {
389 mutex_exit(&zs->zst_lock);
390 goto top;
391 }
392 zs->zst_len += zh->zst_len;
393 diff = zs->zst_len - zfetch_block_cap;
394 if (diff > 0) {
395 zs->zst_offset += diff;
396 zs->zst_len = zs->zst_len > diff ?
397 zs->zst_len - diff : 0;
398 }
399 zs->zst_direction = ZFETCH_FORWARD;
400
401 break;
402
403 /*
404 * Same as above, but reading backwards through the file.
405 */
406 } else if (zh->zst_offset == zs->zst_offset - zh->zst_len) {
407 /* backwards sequential access */
408
409 reset = !prefetched && zs->zst_len > 1;
410
411 mutex_enter(&zs->zst_lock);
412
413 if (zh->zst_offset != zs->zst_offset - zh->zst_len) {
414 mutex_exit(&zs->zst_lock);
415 goto top;
416 }
417
418 zs->zst_offset = zs->zst_offset > zh->zst_len ?
419 zs->zst_offset - zh->zst_len : 0;
420 zs->zst_ph_offset = zs->zst_ph_offset > zh->zst_len ?
421 zs->zst_ph_offset - zh->zst_len : 0;
422 zs->zst_len += zh->zst_len;
423
424 diff = zs->zst_len - zfetch_block_cap;
425 if (diff > 0) {
426 zs->zst_ph_offset = zs->zst_ph_offset > diff ?
427 zs->zst_ph_offset - diff : 0;
428 zs->zst_len = zs->zst_len > diff ?
429 zs->zst_len - diff : zs->zst_len;
430 }
431 zs->zst_direction = ZFETCH_BACKWARD;
432
433 break;
434
435 } else if ((zh->zst_offset - zs->zst_offset - zs->zst_stride <
436 zs->zst_len) && (zs->zst_len != zs->zst_stride)) {
437 /* strided forward access */
438
439 mutex_enter(&zs->zst_lock);
440
441 if ((zh->zst_offset - zs->zst_offset - zs->zst_stride >=
442 zs->zst_len) || (zs->zst_len == zs->zst_stride)) {
443 mutex_exit(&zs->zst_lock);
444 goto top;
445 }
446
447 zs->zst_offset += zs->zst_stride;
448 zs->zst_direction = ZFETCH_FORWARD;
449
450 break;
451
452 } else if ((zh->zst_offset - zs->zst_offset + zs->zst_stride <
453 zs->zst_len) && (zs->zst_len != zs->zst_stride)) {
454 /* strided reverse access */
455
456 mutex_enter(&zs->zst_lock);
457
458 if ((zh->zst_offset - zs->zst_offset + zs->zst_stride >=
459 zs->zst_len) || (zs->zst_len == zs->zst_stride)) {
460 mutex_exit(&zs->zst_lock);
461 goto top;
462 }
463
464 zs->zst_offset = zs->zst_offset > zs->zst_stride ?
465 zs->zst_offset - zs->zst_stride : 0;
466 zs->zst_ph_offset = (zs->zst_ph_offset >
467 (2 * zs->zst_stride)) ?
468 (zs->zst_ph_offset - (2 * zs->zst_stride)) : 0;
469 zs->zst_direction = ZFETCH_BACKWARD;
470
471 break;
472 }
473 }
474
475 if (zs) {
476 if (reset) {
477 zstream_t *remove = zs;
478
479 ZFETCHSTAT_BUMP(zfetchstat_stream_resets);
480 rc = 0;
481 mutex_exit(&zs->zst_lock);
482 rw_exit(&zf->zf_rwlock);
483 rw_enter(&zf->zf_rwlock, RW_WRITER);
484 /*
485 * Relocate the stream, in case someone removes
486 * it while we were acquiring the WRITER lock.
487 */
488 for (zs = list_head(&zf->zf_stream); zs;
489 zs = list_next(&zf->zf_stream, zs)) {
490 if (zs == remove) {
491 dmu_zfetch_stream_remove(zf, zs);
492 mutex_destroy(&zs->zst_lock);
493 kmem_free(zs, sizeof (zstream_t));
494 break;
495 }
496 }
497 } else {
498 ZFETCHSTAT_BUMP(zfetchstat_stream_noresets);
499 rc = 1;
500 dmu_zfetch_dofetch(zf, zs);
501 mutex_exit(&zs->zst_lock);
502 }
503 }
504 out:
505 rw_exit(&zf->zf_rwlock);
506 return (rc);
507 }
508
509 /*
510 * Clean-up state associated with a zfetch structure. This frees allocated
511 * structure members, empties the zf_stream tree, and generally makes things
512 * nice. This doesn't free the zfetch_t itself, that's left to the caller.
513 */
514 void
515 dmu_zfetch_rele(zfetch_t *zf)
516 {
517 zstream_t *zs;
518 zstream_t *zs_next;
519
520 ASSERT(!RW_LOCK_HELD(&zf->zf_rwlock));
521
522 for (zs = list_head(&zf->zf_stream); zs; zs = zs_next) {
523 zs_next = list_next(&zf->zf_stream, zs);
524
525 list_remove(&zf->zf_stream, zs);
526 mutex_destroy(&zs->zst_lock);
527 kmem_free(zs, sizeof (zstream_t));
528 }
529 list_destroy(&zf->zf_stream);
530 rw_destroy(&zf->zf_rwlock);
531
532 zf->zf_dnode = NULL;
533 }
534
535 /*
536 * Given a zfetch and zstream structure, insert the zstream structure into the
537 * AVL tree contained within the zfetch structure. Peform the appropriate
538 * book-keeping. It is possible that another thread has inserted a stream which
539 * matches one that we are about to insert, so we must be sure to check for this
540 * case. If one is found, return failure, and let the caller cleanup the
541 * duplicates.
542 */
543 static int
544 dmu_zfetch_stream_insert(zfetch_t *zf, zstream_t *zs)
545 {
546 zstream_t *zs_walk;
547 zstream_t *zs_next;
548
549 ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
550
551 for (zs_walk = list_head(&zf->zf_stream); zs_walk; zs_walk = zs_next) {
552 zs_next = list_next(&zf->zf_stream, zs_walk);
553
554 if (dmu_zfetch_streams_equal(zs_walk, zs)) {
555 return (0);
556 }
557 }
558
559 list_insert_head(&zf->zf_stream, zs);
560 zf->zf_stream_cnt++;
561 return (1);
562 }
563
564
565 /*
566 * Walk the list of zstreams in the given zfetch, find an old one (by time), and
567 * reclaim it for use by the caller.
568 */
569 static zstream_t *
570 dmu_zfetch_stream_reclaim(zfetch_t *zf)
571 {
572 zstream_t *zs;
573
574 if (! rw_tryenter(&zf->zf_rwlock, RW_WRITER))
575 return (0);
576
577 for (zs = list_head(&zf->zf_stream); zs;
578 zs = list_next(&zf->zf_stream, zs)) {
579
580 if (((ddi_get_lbolt() - zs->zst_last)/hz) > zfetch_min_sec_reap)
581 break;
582 }
583
584 if (zs) {
585 dmu_zfetch_stream_remove(zf, zs);
586 mutex_destroy(&zs->zst_lock);
587 bzero(zs, sizeof (zstream_t));
588 } else {
589 zf->zf_alloc_fail++;
590 }
591 rw_exit(&zf->zf_rwlock);
592
593 return (zs);
594 }
595
596 /*
597 * Given a zfetch and zstream structure, remove the zstream structure from its
598 * container in the zfetch structure. Perform the appropriate book-keeping.
599 */
600 static void
601 dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs)
602 {
603 ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
604
605 list_remove(&zf->zf_stream, zs);
606 zf->zf_stream_cnt--;
607 }
608
609 static int
610 dmu_zfetch_streams_equal(zstream_t *zs1, zstream_t *zs2)
611 {
612 if (zs1->zst_offset != zs2->zst_offset)
613 return (0);
614
615 if (zs1->zst_len != zs2->zst_len)
616 return (0);
617
618 if (zs1->zst_stride != zs2->zst_stride)
619 return (0);
620
621 if (zs1->zst_ph_offset != zs2->zst_ph_offset)
622 return (0);
623
624 if (zs1->zst_cap != zs2->zst_cap)
625 return (0);
626
627 if (zs1->zst_direction != zs2->zst_direction)
628 return (0);
629
630 return (1);
631 }
632
633 /*
634 * This is the prefetch entry point. It calls all of the other dmu_zfetch
635 * routines to create, delete, find, or operate upon prefetch streams.
636 */
637 void
638 dmu_zfetch(zfetch_t *zf, uint64_t offset, uint64_t size, int prefetched)
639 {
640 zstream_t zst;
641 zstream_t *newstream;
642 boolean_t fetched;
643 int inserted;
644 unsigned int blkshft;
645 uint64_t blksz;
646
647 if (zfs_prefetch_disable)
648 return;
649
650 /* files that aren't ln2 blocksz are only one block -- nothing to do */
651 if (!zf->zf_dnode->dn_datablkshift)
652 return;
653
654 /* convert offset and size, into blockid and nblocks */
655 blkshft = zf->zf_dnode->dn_datablkshift;
656 blksz = (1 << blkshft);
657
658 bzero(&zst, sizeof (zstream_t));
659 zst.zst_offset = offset >> blkshft;
660 zst.zst_len = (P2ROUNDUP(offset + size, blksz) -
661 P2ALIGN(offset, blksz)) >> blkshft;
662
663 fetched = dmu_zfetch_find(zf, &zst, prefetched);
664 if (fetched) {
665 ZFETCHSTAT_BUMP(zfetchstat_hits);
666 } else {
667 ZFETCHSTAT_BUMP(zfetchstat_misses);
668 fetched = dmu_zfetch_colinear(zf, &zst);
669 if (fetched) {
670 ZFETCHSTAT_BUMP(zfetchstat_colinear_hits);
671 } else {
672 ZFETCHSTAT_BUMP(zfetchstat_colinear_misses);
673 }
674 }
675
676 if (!fetched) {
677 newstream = dmu_zfetch_stream_reclaim(zf);
678
679 /*
680 * we still couldn't find a stream, drop the lock, and allocate
681 * one if possible. Otherwise, give up and go home.
682 */
683 if (newstream) {
684 ZFETCHSTAT_BUMP(zfetchstat_reclaim_successes);
685 } else {
686 uint64_t maxblocks;
687 uint32_t max_streams;
688 uint32_t cur_streams;
689
690 ZFETCHSTAT_BUMP(zfetchstat_reclaim_failures);
691 cur_streams = zf->zf_stream_cnt;
692 maxblocks = zf->zf_dnode->dn_maxblkid;
693
694 max_streams = MIN(zfetch_max_streams,
695 (maxblocks / zfetch_block_cap));
696 if (max_streams == 0) {
697 max_streams++;
698 }
699
700 if (cur_streams >= max_streams) {
701 return;
702 }
703 newstream = kmem_zalloc(sizeof (zstream_t), KM_SLEEP);
704 }
705
706 newstream->zst_offset = zst.zst_offset;
707 newstream->zst_len = zst.zst_len;
708 newstream->zst_stride = zst.zst_len;
709 newstream->zst_ph_offset = zst.zst_len + zst.zst_offset;
710 newstream->zst_cap = zst.zst_len;
711 newstream->zst_direction = ZFETCH_FORWARD;
712 newstream->zst_last = ddi_get_lbolt();
713
714 mutex_init(&newstream->zst_lock, NULL, MUTEX_DEFAULT, NULL);
715
716 rw_enter(&zf->zf_rwlock, RW_WRITER);
717 inserted = dmu_zfetch_stream_insert(zf, newstream);
718 rw_exit(&zf->zf_rwlock);
719
720 if (!inserted) {
721 mutex_destroy(&newstream->zst_lock);
722 kmem_free(newstream, sizeof (zstream_t));
723 }
724 }
725 }