3741 zfs needs better comments
Submitted by:   Will Andrews <willa@spectralogic.com>
Submitted by:   Justin Gibbs <justing@spectralogic.com>
Submitted by:   Alan Somers <alans@spectralogic.com>
Reviewed by:    Matthew Ahrens <mahrens@delphix.com>

*** 46,60 ****
  uint32_t        zfetch_block_cap = 256;
  /* number of bytes in a array_read at which we stop prefetching (1Mb) */
  uint64_t        zfetch_array_rd_sz = 1024 * 1024;
  
  /* forward decls for static routines */
! static int              dmu_zfetch_colinear(zfetch_t *, zstream_t *);
  static void             dmu_zfetch_dofetch(zfetch_t *, zstream_t *);
  static uint64_t         dmu_zfetch_fetch(dnode_t *, uint64_t, uint64_t);
  static uint64_t         dmu_zfetch_fetchsz(dnode_t *, uint64_t, uint64_t);
! static int              dmu_zfetch_find(zfetch_t *, zstream_t *, int);
  static int              dmu_zfetch_stream_insert(zfetch_t *, zstream_t *);
  static zstream_t        *dmu_zfetch_stream_reclaim(zfetch_t *);
  static void             dmu_zfetch_stream_remove(zfetch_t *, zstream_t *);
  static int              dmu_zfetch_streams_equal(zstream_t *, zstream_t *);
  
--- 46,60 ----
  uint32_t        zfetch_block_cap = 256;
  /* number of bytes in a array_read at which we stop prefetching (1Mb) */
  uint64_t        zfetch_array_rd_sz = 1024 * 1024;
  
  /* forward decls for static routines */
! static boolean_t        dmu_zfetch_colinear(zfetch_t *, zstream_t *);
  static void             dmu_zfetch_dofetch(zfetch_t *, zstream_t *);
  static uint64_t         dmu_zfetch_fetch(dnode_t *, uint64_t, uint64_t);
  static uint64_t         dmu_zfetch_fetchsz(dnode_t *, uint64_t, uint64_t);
! static boolean_t        dmu_zfetch_find(zfetch_t *, zstream_t *, int);
  static int              dmu_zfetch_stream_insert(zfetch_t *, zstream_t *);
  static zstream_t        *dmu_zfetch_stream_reclaim(zfetch_t *);
  static void             dmu_zfetch_stream_remove(zfetch_t *, zstream_t *);
  static int              dmu_zfetch_streams_equal(zstream_t *, zstream_t *);
  
*** 102,114 ****
   * In other words: if we find two sequential access streams that are
   * the same length and distance N appart, and this read is N from the
   * last stream, then we are probably in a strided access pattern.  So
   * combine the two sequential streams into a single strided stream.
   *
!  * If no co-linear streams are found, return NULL.
   */
! static int
  dmu_zfetch_colinear(zfetch_t *zf, zstream_t *zh)
  {
          zstream_t       *z_walk;
          zstream_t       *z_comp;
  
--- 102,114 ----
   * In other words: if we find two sequential access streams that are
   * the same length and distance N appart, and this read is N from the
   * last stream, then we are probably in a strided access pattern.  So
   * combine the two sequential streams into a single strided stream.
   *
!  * Returns whether co-linear streams were found.
   */
! static boolean_t
  dmu_zfetch_colinear(zfetch_t *zf, zstream_t *zh)
  {
          zstream_t       *z_walk;
          zstream_t       *z_comp;
  
*** 324,334 ****
  /*
   * given a zfetch and a zstream structure, see if there is an associated zstream
   * for this block read.  If so, it starts a prefetch for the stream it
   * located and returns true, otherwise it returns false
   */
! static int
  dmu_zfetch_find(zfetch_t *zf, zstream_t *zh, int prefetched)
  {
          zstream_t       *zs;
          int64_t         diff;
          int             reset = !prefetched;
--- 324,334 ----
  /*
   * given a zfetch and a zstream structure, see if there is an associated zstream
   * for this block read.  If so, it starts a prefetch for the stream it
   * located and returns true, otherwise it returns false
   */
! static boolean_t
  dmu_zfetch_find(zfetch_t *zf, zstream_t *zh, int prefetched)
  {
          zstream_t       *zs;
          int64_t         diff;
          int             reset = !prefetched;
*** 637,647 ****
  void
  dmu_zfetch(zfetch_t *zf, uint64_t offset, uint64_t size, int prefetched)
  {
          zstream_t       zst;
          zstream_t       *newstream;
!         int             fetched;
          int             inserted;
          unsigned int    blkshft;
          uint64_t        blksz;
  
          if (zfs_prefetch_disable)
--- 637,647 ----
  void
  dmu_zfetch(zfetch_t *zf, uint64_t offset, uint64_t size, int prefetched)
  {
          zstream_t       zst;
          zstream_t       *newstream;
!         boolean_t       fetched;
          int             inserted;
          unsigned int    blkshft;
          uint64_t        blksz;
  
          if (zfs_prefetch_disable)
*** 663,673 ****
          fetched = dmu_zfetch_find(zf, &zst, prefetched);
          if (fetched) {
                  ZFETCHSTAT_BUMP(zfetchstat_hits);
          } else {
                  ZFETCHSTAT_BUMP(zfetchstat_misses);
!                 if (fetched = dmu_zfetch_colinear(zf, &zst)) {
                          ZFETCHSTAT_BUMP(zfetchstat_colinear_hits);
                  } else {
                          ZFETCHSTAT_BUMP(zfetchstat_colinear_misses);
                  }
          }
--- 663,674 ----
          fetched = dmu_zfetch_find(zf, &zst, prefetched);
          if (fetched) {
                  ZFETCHSTAT_BUMP(zfetchstat_hits);
          } else {
                  ZFETCHSTAT_BUMP(zfetchstat_misses);
!                 fetched = dmu_zfetch_colinear(zf, &zst);
!                 if (fetched) {
                          ZFETCHSTAT_BUMP(zfetchstat_colinear_hits);
                  } else {
                          ZFETCHSTAT_BUMP(zfetchstat_colinear_misses);
                  }
          }