diff options
Diffstat (limited to 'module/zfs/dmu_zfetch.c')
| -rw-r--r-- | module/zfs/dmu_zfetch.c | 723 |
1 files changed, 140 insertions, 583 deletions
diff --git a/module/zfs/dmu_zfetch.c b/module/zfs/dmu_zfetch.c index 9d41bdc0f..b25b0e007 100644 --- a/module/zfs/dmu_zfetch.c +++ b/module/zfs/dmu_zfetch.c @@ -24,7 +24,7 @@ */ /* - * Copyright (c) 2013 by Delphix. All rights reserved. + * Copyright (c) 2013, 2014 by Delphix. All rights reserved. */ #include <sys/zfs_context.h> @@ -36,209 +36,43 @@ #include <sys/kstat.h> /* - * I'm against tune-ables, but these should probably exist as tweakable globals - * until we can get this working the way we want it to. + * This tunable disables predictive prefetch. Note that it leaves "prescient" + * prefetch (e.g. prefetch for zfs send) intact. Unlike predictive prefetch, + * prescient prefetch never issues i/os that end up not being needed, + * so it can't hurt performance. */ -int zfs_prefetch_disable = 0; +int zfs_prefetch_disable = B_FALSE; /* max # of streams per zfetch */ unsigned int zfetch_max_streams = 8; /* min time before stream reclaim */ unsigned int zfetch_min_sec_reap = 2; -/* max number of blocks to fetch at a time */ -unsigned int zfetch_block_cap = 256; -/* number of bytes in a array_read at which we stop prefetching (1Mb) */ +/* max bytes to prefetch per stream (default 8MB) */ +unsigned int zfetch_max_distance = 8 * 1024 * 1024; +/* number of bytes in a array_read at which we stop prefetching (1MB) */ unsigned long 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 *); - typedef struct zfetch_stats { kstat_named_t zfetchstat_hits; kstat_named_t zfetchstat_misses; - kstat_named_t zfetchstat_colinear_hits; - kstat_named_t zfetchstat_colinear_misses; - kstat_named_t zfetchstat_stride_hits; - kstat_named_t zfetchstat_stride_misses; - kstat_named_t zfetchstat_reclaim_successes; - kstat_named_t zfetchstat_reclaim_failures; - kstat_named_t zfetchstat_stream_resets; - kstat_named_t zfetchstat_stream_noresets; - kstat_named_t zfetchstat_bogus_streams; + kstat_named_t zfetchstat_max_streams; } zfetch_stats_t; static zfetch_stats_t zfetch_stats = { { "hits", KSTAT_DATA_UINT64 }, { "misses", KSTAT_DATA_UINT64 }, - { "colinear_hits", KSTAT_DATA_UINT64 }, - { "colinear_misses", KSTAT_DATA_UINT64 }, - { "stride_hits", KSTAT_DATA_UINT64 }, - { "stride_misses", KSTAT_DATA_UINT64 }, - { "reclaim_successes", KSTAT_DATA_UINT64 }, - { "reclaim_failures", KSTAT_DATA_UINT64 }, - { "streams_resets", KSTAT_DATA_UINT64 }, - { "streams_noresets", KSTAT_DATA_UINT64 }, - { "bogus_streams", KSTAT_DATA_UINT64 }, + { "max_streams", KSTAT_DATA_UINT64 }, }; -#define ZFETCHSTAT_INCR(stat, val) \ - atomic_add_64(&zfetch_stats.stat.value.ui64, (val)); - -#define ZFETCHSTAT_BUMP(stat) ZFETCHSTAT_INCR(stat, 1); +#define ZFETCHSTAT_BUMP(stat) \ + atomic_inc_64(&zfetch_stats.stat.value.ui64); kstat_t *zfetch_ksp; -/* - * Given a zfetch structure and a zstream structure, determine whether the - * blocks to be read are part of a co-linear pair of existing prefetch - * streams. If a set is found, coalesce the streams, removing one, and - * configure the prefetch so it looks for a strided access pattern. - * - * 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; - - if (! rw_tryenter(&zf->zf_rwlock, RW_WRITER)) - return (0); - - if (zh == NULL) { - rw_exit(&zf->zf_rwlock); - return (0); - } - - for (z_walk = list_head(&zf->zf_stream); z_walk; - z_walk = list_next(&zf->zf_stream, z_walk)) { - for (z_comp = list_next(&zf->zf_stream, z_walk); z_comp; - z_comp = list_next(&zf->zf_stream, z_comp)) { - int64_t diff; - - if (z_walk->zst_len != z_walk->zst_stride || - z_comp->zst_len != z_comp->zst_stride) { - continue; - } - - diff = z_comp->zst_offset - z_walk->zst_offset; - if (z_comp->zst_offset + diff == zh->zst_offset) { - z_walk->zst_offset = zh->zst_offset; - z_walk->zst_direction = diff < 0 ? - ZFETCH_BACKWARD : ZFETCH_FORWARD; - z_walk->zst_stride = - diff * z_walk->zst_direction; - z_walk->zst_ph_offset = - zh->zst_offset + z_walk->zst_stride; - dmu_zfetch_stream_remove(zf, z_comp); - mutex_destroy(&z_comp->zst_lock); - kmem_free(z_comp, sizeof (zstream_t)); - - dmu_zfetch_dofetch(zf, z_walk); - - rw_exit(&zf->zf_rwlock); - return (1); - } - - diff = z_walk->zst_offset - z_comp->zst_offset; - if (z_walk->zst_offset + diff == zh->zst_offset) { - z_walk->zst_offset = zh->zst_offset; - z_walk->zst_direction = diff < 0 ? - ZFETCH_BACKWARD : ZFETCH_FORWARD; - z_walk->zst_stride = - diff * z_walk->zst_direction; - z_walk->zst_ph_offset = - zh->zst_offset + z_walk->zst_stride; - dmu_zfetch_stream_remove(zf, z_comp); - mutex_destroy(&z_comp->zst_lock); - kmem_free(z_comp, sizeof (zstream_t)); - - dmu_zfetch_dofetch(zf, z_walk); - - rw_exit(&zf->zf_rwlock); - return (1); - } - } - } - - rw_exit(&zf->zf_rwlock); - return (0); -} - -/* - * Given a zstream_t, determine the bounds of the prefetch. Then call the - * routine that actually prefetches the individual blocks. - */ -static void -dmu_zfetch_dofetch(zfetch_t *zf, zstream_t *zs) -{ - uint64_t prefetch_tail; - uint64_t prefetch_limit; - uint64_t prefetch_ofst; - uint64_t prefetch_len; - uint64_t blocks_fetched; - - zs->zst_stride = MAX((int64_t)zs->zst_stride, zs->zst_len); - zs->zst_cap = MIN(zfetch_block_cap, 2 * zs->zst_cap); - - prefetch_tail = MAX((int64_t)zs->zst_ph_offset, - (int64_t)(zs->zst_offset + zs->zst_stride)); - /* - * XXX: use a faster division method? - */ - prefetch_limit = zs->zst_offset + zs->zst_len + - (zs->zst_cap * zs->zst_stride) / zs->zst_len; - - while (prefetch_tail < prefetch_limit) { - prefetch_ofst = zs->zst_offset + zs->zst_direction * - (prefetch_tail - zs->zst_offset); - - prefetch_len = zs->zst_len; - - /* - * Don't prefetch beyond the end of the file, if working - * backwards. - */ - if ((zs->zst_direction == ZFETCH_BACKWARD) && - (prefetch_ofst > prefetch_tail)) { - prefetch_len += prefetch_ofst; - prefetch_ofst = 0; - } - - /* don't prefetch more than we're supposed to */ - if (prefetch_len > zs->zst_len) - break; - - blocks_fetched = dmu_zfetch_fetch(zf->zf_dnode, - prefetch_ofst, zs->zst_len); - - prefetch_tail += zs->zst_stride; - /* stop if we've run out of stuff to prefetch */ - if (blocks_fetched < zs->zst_len) - break; - } - zs->zst_ph_offset = prefetch_tail; - zs->zst_last = ddi_get_lbolt(); -} - void zfetch_init(void) { - zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc", KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t), KSTAT_FLAG_VIRTUAL); @@ -266,273 +100,41 @@ zfetch_fini(void) void dmu_zfetch_init(zfetch_t *zf, dnode_t *dno) { - if (zf == NULL) { + if (zf == NULL) return; - } zf->zf_dnode = dno; - zf->zf_stream_cnt = 0; - zf->zf_alloc_fail = 0; list_create(&zf->zf_stream, sizeof (zstream_t), - offsetof(zstream_t, zst_node)); + offsetof(zstream_t, zs_node)); rw_init(&zf->zf_rwlock, NULL, RW_DEFAULT, NULL); } -/* - * This function computes the actual size, in blocks, that can be prefetched, - * and fetches it. - */ -static uint64_t -dmu_zfetch_fetch(dnode_t *dn, uint64_t blkid, uint64_t nblks) -{ - uint64_t fetchsz; - uint64_t i; - - fetchsz = dmu_zfetch_fetchsz(dn, blkid, nblks); - - for (i = 0; i < fetchsz; i++) { - dbuf_prefetch(dn, 0, blkid + i, ZIO_PRIORITY_ASYNC_READ, - ARC_FLAG_PREFETCH); - } - - return (fetchsz); -} - -/* - * this function returns the number of blocks that would be prefetched, based - * upon the supplied dnode, blockid, and nblks. This is used so that we can - * update streams in place, and then prefetch with their old value after the - * fact. This way, we can delay the prefetch, but subsequent accesses to the - * stream won't result in the same data being prefetched multiple times. - */ -static uint64_t -dmu_zfetch_fetchsz(dnode_t *dn, uint64_t blkid, uint64_t nblks) -{ - uint64_t fetchsz; - - if (blkid > dn->dn_maxblkid) { - return (0); - } - - /* compute fetch size */ - if (blkid + nblks + 1 > dn->dn_maxblkid) { - fetchsz = (dn->dn_maxblkid - blkid) + 1; - ASSERT(blkid + fetchsz - 1 <= dn->dn_maxblkid); - } else { - fetchsz = nblks; - } - - - return (fetchsz); -} - -/* - * 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) +static void +dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs) { - zstream_t *zs; - int64_t diff; - int reset = !prefetched; - int rc = 0; - - if (zh == NULL) - return (0); - - /* - * XXX: This locking strategy is a bit coarse; however, it's impact has - * yet to be tested. If this turns out to be an issue, it can be - * modified in a number of different ways. - */ - - rw_enter(&zf->zf_rwlock, RW_READER); -top: - - for (zs = list_head(&zf->zf_stream); zs; - zs = list_next(&zf->zf_stream, zs)) { - - /* - * XXX - should this be an assert? - */ - if (zs->zst_len == 0) { - /* bogus stream */ - ZFETCHSTAT_BUMP(zfetchstat_bogus_streams); - continue; - } - - /* - * We hit this case when we are in a strided prefetch stream: - * we will read "len" blocks before "striding". - */ - if (zh->zst_offset >= zs->zst_offset && - zh->zst_offset < zs->zst_offset + zs->zst_len) { - if (prefetched) { - /* already fetched */ - ZFETCHSTAT_BUMP(zfetchstat_stride_hits); - rc = 1; - goto out; - } else { - ZFETCHSTAT_BUMP(zfetchstat_stride_misses); - } - } - - /* - * This is the forward sequential read case: we increment - * len by one each time we hit here, so we will enter this - * case on every read. - */ - if (zh->zst_offset == zs->zst_offset + zs->zst_len) { - - reset = !prefetched && zs->zst_len > 1; - - mutex_enter(&zs->zst_lock); - - if (zh->zst_offset != zs->zst_offset + zs->zst_len) { - mutex_exit(&zs->zst_lock); - goto top; - } - zs->zst_len += zh->zst_len; - diff = zs->zst_len - zfetch_block_cap; - if (diff > 0) { - zs->zst_offset += diff; - zs->zst_len = zs->zst_len > diff ? - zs->zst_len - diff : 0; - } - zs->zst_direction = ZFETCH_FORWARD; - - break; - - /* - * Same as above, but reading backwards through the file. - */ - } else if (zh->zst_offset == zs->zst_offset - zh->zst_len) { - /* backwards sequential access */ - - reset = !prefetched && zs->zst_len > 1; - - mutex_enter(&zs->zst_lock); - - if (zh->zst_offset != zs->zst_offset - zh->zst_len) { - mutex_exit(&zs->zst_lock); - goto top; - } - - zs->zst_offset = zs->zst_offset > zh->zst_len ? - zs->zst_offset - zh->zst_len : 0; - zs->zst_ph_offset = zs->zst_ph_offset > zh->zst_len ? - zs->zst_ph_offset - zh->zst_len : 0; - zs->zst_len += zh->zst_len; - - diff = zs->zst_len - zfetch_block_cap; - if (diff > 0) { - zs->zst_ph_offset = zs->zst_ph_offset > diff ? - zs->zst_ph_offset - diff : 0; - zs->zst_len = zs->zst_len > diff ? - zs->zst_len - diff : zs->zst_len; - } - zs->zst_direction = ZFETCH_BACKWARD; - - break; - - } else if ((zh->zst_offset - zs->zst_offset - zs->zst_stride < - zs->zst_len) && (zs->zst_len != zs->zst_stride)) { - /* strided forward access */ - - mutex_enter(&zs->zst_lock); - - if ((zh->zst_offset - zs->zst_offset - zs->zst_stride >= - zs->zst_len) || (zs->zst_len == zs->zst_stride)) { - mutex_exit(&zs->zst_lock); - goto top; - } - - zs->zst_offset += zs->zst_stride; - zs->zst_direction = ZFETCH_FORWARD; - - break; - - } else if ((zh->zst_offset - zs->zst_offset + zs->zst_stride < - zs->zst_len) && (zs->zst_len != zs->zst_stride)) { - /* strided reverse access */ - - mutex_enter(&zs->zst_lock); - - if ((zh->zst_offset - zs->zst_offset + zs->zst_stride >= - zs->zst_len) || (zs->zst_len == zs->zst_stride)) { - mutex_exit(&zs->zst_lock); - goto top; - } - - zs->zst_offset = zs->zst_offset > zs->zst_stride ? - zs->zst_offset - zs->zst_stride : 0; - zs->zst_ph_offset = (zs->zst_ph_offset > - (2 * zs->zst_stride)) ? - (zs->zst_ph_offset - (2 * zs->zst_stride)) : 0; - zs->zst_direction = ZFETCH_BACKWARD; - - break; - } - } - - if (zs) { - if (reset) { - zstream_t *remove = zs; - - ZFETCHSTAT_BUMP(zfetchstat_stream_resets); - rc = 0; - mutex_exit(&zs->zst_lock); - rw_exit(&zf->zf_rwlock); - rw_enter(&zf->zf_rwlock, RW_WRITER); - /* - * Relocate the stream, in case someone removes - * it while we were acquiring the WRITER lock. - */ - for (zs = list_head(&zf->zf_stream); zs; - zs = list_next(&zf->zf_stream, zs)) { - if (zs == remove) { - dmu_zfetch_stream_remove(zf, zs); - mutex_destroy(&zs->zst_lock); - kmem_free(zs, sizeof (zstream_t)); - break; - } - } - } else { - ZFETCHSTAT_BUMP(zfetchstat_stream_noresets); - rc = 1; - dmu_zfetch_dofetch(zf, zs); - mutex_exit(&zs->zst_lock); - } - } -out: - rw_exit(&zf->zf_rwlock); - return (rc); + ASSERT(RW_WRITE_HELD(&zf->zf_rwlock)); + list_remove(&zf->zf_stream, zs); + mutex_destroy(&zs->zs_lock); + kmem_free(zs, sizeof (*zs)); } /* - * Clean-up state associated with a zfetch structure. This frees allocated - * structure members, empties the zf_stream tree, and generally makes things - * nice. This doesn't free the zfetch_t itself, that's left to the caller. + * Clean-up state associated with a zfetch structure (e.g. destroy the + * streams). This doesn't free the zfetch_t itself, that's left to the caller. */ void -dmu_zfetch_rele(zfetch_t *zf) +dmu_zfetch_fini(zfetch_t *zf) { - zstream_t *zs; - zstream_t *zs_next; + zstream_t *zs; ASSERT(!RW_LOCK_HELD(&zf->zf_rwlock)); - for (zs = list_head(&zf->zf_stream); zs; zs = zs_next) { - zs_next = list_next(&zf->zf_stream, zs); - - list_remove(&zf->zf_stream, zs); - mutex_destroy(&zs->zst_lock); - kmem_free(zs, sizeof (zstream_t)); - } + rw_enter(&zf->zf_rwlock, RW_WRITER); + while ((zs = list_head(&zf->zf_stream)) != NULL) + dmu_zfetch_stream_remove(zf, zs); + rw_exit(&zf->zf_rwlock); list_destroy(&zf->zf_stream); rw_destroy(&zf->zf_rwlock); @@ -540,101 +142,57 @@ dmu_zfetch_rele(zfetch_t *zf) } /* - * Given a zfetch and zstream structure, insert the zstream structure into the - * AVL tree contained within the zfetch structure. Peform the appropriate - * book-keeping. It is possible that another thread has inserted a stream which - * matches one that we are about to insert, so we must be sure to check for this - * case. If one is found, return failure, and let the caller cleanup the - * duplicates. + * If there aren't too many streams already, create a new stream. + * The "blkid" argument is the next block that we expect this stream to access. + * While we're here, clean up old streams (which haven't been + * accessed for at least zfetch_min_sec_reap seconds). */ -static int -dmu_zfetch_stream_insert(zfetch_t *zf, zstream_t *zs) +static void +dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid) { - zstream_t *zs_walk; - zstream_t *zs_next; + zstream_t *zs; + zstream_t *zs_next; + int numstreams = 0; + uint32_t max_streams; ASSERT(RW_WRITE_HELD(&zf->zf_rwlock)); - for (zs_walk = list_head(&zf->zf_stream); zs_walk; zs_walk = zs_next) { - zs_next = list_next(&zf->zf_stream, zs_walk); - - if (dmu_zfetch_streams_equal(zs_walk, zs)) { - return (0); - } - } - - list_insert_head(&zf->zf_stream, zs); - zf->zf_stream_cnt++; - return (1); -} - - -/* - * Walk the list of zstreams in the given zfetch, find an old one (by time), and - * reclaim it for use by the caller. - */ -static zstream_t * -dmu_zfetch_stream_reclaim(zfetch_t *zf) -{ - zstream_t *zs; - - if (! rw_tryenter(&zf->zf_rwlock, RW_WRITER)) - return (0); - - for (zs = list_head(&zf->zf_stream); zs; - zs = list_next(&zf->zf_stream, zs)) { - - if (((ddi_get_lbolt() - zs->zst_last)/hz) > zfetch_min_sec_reap) - break; + /* + * Clean up old streams. + */ + for (zs = list_head(&zf->zf_stream); + zs != NULL; zs = zs_next) { + zs_next = list_next(&zf->zf_stream, zs); + if (((gethrtime() - zs->zs_atime) / NANOSEC) > + zfetch_min_sec_reap) + dmu_zfetch_stream_remove(zf, zs); + else + numstreams++; } - if (zs) { - dmu_zfetch_stream_remove(zf, zs); - mutex_destroy(&zs->zst_lock); - bzero(zs, sizeof (zstream_t)); - } else { - zf->zf_alloc_fail++; + /* + * The maximum number of streams is normally zfetch_max_streams, + * but for small files we lower it such that it's at least possible + * for all the streams to be non-overlapping. + * + * If we are already at the maximum number of streams for this file, + * even after removing old streams, then don't create this stream. + */ + max_streams = MAX(1, MIN(zfetch_max_streams, + zf->zf_dnode->dn_maxblkid * zf->zf_dnode->dn_datablksz / + zfetch_max_distance)); + if (numstreams >= max_streams) { + ZFETCHSTAT_BUMP(zfetchstat_max_streams); + return; } - rw_exit(&zf->zf_rwlock); - - return (zs); -} -/* - * Given a zfetch and zstream structure, remove the zstream structure from its - * container in the zfetch structure. Perform the appropriate book-keeping. - */ -static void -dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs) -{ - ASSERT(RW_WRITE_HELD(&zf->zf_rwlock)); + zs = kmem_zalloc(sizeof (*zs), KM_SLEEP); + zs->zs_blkid = blkid; + zs->zs_pf_blkid = blkid; + zs->zs_atime = gethrtime(); + mutex_init(&zs->zs_lock, NULL, MUTEX_DEFAULT, NULL); - list_remove(&zf->zf_stream, zs); - zf->zf_stream_cnt--; -} - -static int -dmu_zfetch_streams_equal(zstream_t *zs1, zstream_t *zs2) -{ - if (zs1->zst_offset != zs2->zst_offset) - return (0); - - if (zs1->zst_len != zs2->zst_len) - return (0); - - if (zs1->zst_stride != zs2->zst_stride) - return (0); - - if (zs1->zst_ph_offset != zs2->zst_ph_offset) - return (0); - - if (zs1->zst_cap != zs2->zst_cap) - return (0); - - if (zs1->zst_direction != zs2->zst_direction) - return (0); - - return (1); + list_insert_head(&zf->zf_stream, zs); } /* @@ -642,93 +200,91 @@ dmu_zfetch_streams_equal(zstream_t *zs1, zstream_t *zs2) * routines to create, delete, find, or operate upon prefetch streams. */ void -dmu_zfetch(zfetch_t *zf, uint64_t offset, uint64_t size, int prefetched) +dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks) { - zstream_t zst; - zstream_t *newstream; - boolean_t fetched; - int inserted; - unsigned int blkshft; - uint64_t blksz; + zstream_t *zs; + int64_t pf_start; + int pf_nblks; + int i; if (zfs_prefetch_disable) return; - /* files that aren't ln2 blocksz are only one block -- nothing to do */ - if (!zf->zf_dnode->dn_datablkshift) + /* + * As a fast path for small (single-block) files, ignore access + * to the first block. + */ + if (blkid == 0) return; - /* convert offset and size, into blockid and nblocks */ - blkshft = zf->zf_dnode->dn_datablkshift; - blksz = (1 << blkshft); - - bzero(&zst, sizeof (zstream_t)); - zst.zst_offset = offset >> blkshft; - zst.zst_len = (P2ROUNDUP(offset + size, blksz) - - P2ALIGN(offset, blksz)) >> blkshft; + rw_enter(&zf->zf_rwlock, RW_READER); - 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); + for (zs = list_head(&zf->zf_stream); zs != NULL; + zs = list_next(&zf->zf_stream, zs)) { + if (blkid == zs->zs_blkid) { + mutex_enter(&zs->zs_lock); + /* + * zs_blkid could have changed before we + * acquired zs_lock; re-check them here. + */ + if (blkid != zs->zs_blkid) { + mutex_exit(&zs->zs_lock); + continue; + } + break; } } - if (!fetched) { - newstream = dmu_zfetch_stream_reclaim(zf); - + if (zs == NULL) { /* - * we still couldn't find a stream, drop the lock, and allocate - * one if possible. Otherwise, give up and go home. + * This access is not part of any existing stream. Create + * a new stream for it. */ - if (newstream) { - ZFETCHSTAT_BUMP(zfetchstat_reclaim_successes); - } else { - uint64_t maxblocks; - uint32_t max_streams; - uint32_t cur_streams; - - ZFETCHSTAT_BUMP(zfetchstat_reclaim_failures); - cur_streams = zf->zf_stream_cnt; - maxblocks = zf->zf_dnode->dn_maxblkid; - - max_streams = MIN(zfetch_max_streams, - (maxblocks / zfetch_block_cap)); - if (max_streams == 0) { - max_streams++; - } - - if (cur_streams >= max_streams) { - return; - } - newstream = - kmem_zalloc(sizeof (zstream_t), KM_SLEEP); - } + ZFETCHSTAT_BUMP(zfetchstat_misses); + if (rw_tryupgrade(&zf->zf_rwlock)) + dmu_zfetch_stream_create(zf, blkid + nblks); + rw_exit(&zf->zf_rwlock); + return; + } - newstream->zst_offset = zst.zst_offset; - newstream->zst_len = zst.zst_len; - newstream->zst_stride = zst.zst_len; - newstream->zst_ph_offset = zst.zst_len + zst.zst_offset; - newstream->zst_cap = zst.zst_len; - newstream->zst_direction = ZFETCH_FORWARD; - newstream->zst_last = ddi_get_lbolt(); + /* + * This access was to a block that we issued a prefetch for on + * behalf of this stream. Issue further prefetches for this stream. + * + * Normally, we start prefetching where we stopped + * prefetching last (zs_pf_blkid). But when we get our first + * hit on this stream, zs_pf_blkid == zs_blkid, we don't + * want to prefetch to block we just accessed. In this case, + * start just after the block we just accessed. + */ + pf_start = MAX(zs->zs_pf_blkid, blkid + nblks); - mutex_init(&newstream->zst_lock, NULL, MUTEX_DEFAULT, NULL); + /* + * Double our amount of prefetched data, but don't let the + * prefetch get further ahead than zfetch_max_distance. + */ + pf_nblks = + MIN((int64_t)zs->zs_pf_blkid - zs->zs_blkid + nblks, + zs->zs_blkid + nblks + + (zfetch_max_distance >> zf->zf_dnode->dn_datablkshift) - pf_start); - rw_enter(&zf->zf_rwlock, RW_WRITER); - inserted = dmu_zfetch_stream_insert(zf, newstream); - rw_exit(&zf->zf_rwlock); + zs->zs_pf_blkid = pf_start + pf_nblks; + zs->zs_atime = gethrtime(); + zs->zs_blkid = blkid + nblks; - if (!inserted) { - mutex_destroy(&newstream->zst_lock); - kmem_free(newstream, sizeof (zstream_t)); - } + /* + * dbuf_prefetch() issues the prefetch i/o + * asynchronously, but it may need to wait for an + * indirect block to be read from disk. Therefore + * we do not want to hold any locks while we call it. + */ + mutex_exit(&zs->zs_lock); + rw_exit(&zf->zf_rwlock); + for (i = 0; i < pf_nblks; i++) { + dbuf_prefetch(zf->zf_dnode, 0, pf_start + i, + ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH); } + ZFETCHSTAT_BUMP(zfetchstat_hits); } #if defined(_KERNEL) && defined(HAVE_SPL) @@ -741,8 +297,9 @@ MODULE_PARM_DESC(zfetch_max_streams, "Max number of streams per zfetch"); module_param(zfetch_min_sec_reap, uint, 0644); MODULE_PARM_DESC(zfetch_min_sec_reap, "Min time before stream reclaim"); -module_param(zfetch_block_cap, uint, 0644); -MODULE_PARM_DESC(zfetch_block_cap, "Max number of blocks to fetch at a time"); +module_param(zfetch_max_distance, uint, 0644); +MODULE_PARM_DESC(zfetch_max_distance, + "Max bytes to prefetch per stream (default 8MB)"); module_param(zfetch_array_rd_sz, ulong, 0644); MODULE_PARM_DESC(zfetch_array_rd_sz, "Number of bytes in a array_read"); |