/* * CDDL HEADER START * * The contents of this file are subject to the terms of the * Common Development and Distribution License (the "License"). * You may not use this file except in compliance with the License. * * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE * or http://www.opensolaris.org/os/licensing. * See the License for the specific language governing permissions * and limitations under the License. * * When distributing Covered Code, include this CDDL HEADER in each * file and include the License file at usr/src/OPENSOLARIS.LICENSE. * If applicable, add the following below this CDDL HEADER, with the * fields enclosed by brackets "[]" replaced with your own identifying * information: Portions Copyright [yyyy] [name of copyright owner] * * CDDL HEADER END */ /* * Copyright 2009 Sun Microsystems, Inc. All rights reserved. * Use is subject to license terms. */ /* * Copyright (c) 2013, 2017 by Delphix. All rights reserved. */ #include #include #include #include #include #include #include #include /* * 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. */ static int zfs_prefetch_disable = B_FALSE; /* max # of streams per zfetch */ static unsigned int zfetch_max_streams = 8; /* min time before stream reclaim */ static unsigned int zfetch_min_sec_reap = 2; /* max bytes to prefetch per stream (default 8MB) */ unsigned int zfetch_max_distance = 8 * 1024 * 1024; /* max bytes to prefetch indirects for per stream (default 64MB) */ unsigned int zfetch_max_idistance = 64 * 1024 * 1024; /* max number of bytes in an array_read in which we allow prefetching (1MB) */ unsigned long zfetch_array_rd_sz = 1024 * 1024; typedef struct zfetch_stats { kstat_named_t zfetchstat_hits; kstat_named_t zfetchstat_misses; kstat_named_t zfetchstat_max_streams; kstat_named_t zfetchstat_io_issued; } zfetch_stats_t; static zfetch_stats_t zfetch_stats = { { "hits", KSTAT_DATA_UINT64 }, { "misses", KSTAT_DATA_UINT64 }, { "max_streams", KSTAT_DATA_UINT64 }, { "io_issued", KSTAT_DATA_UINT64 }, }; struct { wmsum_t zfetchstat_hits; wmsum_t zfetchstat_misses; wmsum_t zfetchstat_max_streams; wmsum_t zfetchstat_io_issued; } zfetch_sums; #define ZFETCHSTAT_BUMP(stat) \ wmsum_add(&zfetch_sums.stat, 1) #define ZFETCHSTAT_ADD(stat, val) \ wmsum_add(&zfetch_sums.stat, val) static kstat_t *zfetch_ksp; static int zfetch_kstats_update(kstat_t *ksp, int rw) { zfetch_stats_t *zs = ksp->ks_data; if (rw == KSTAT_WRITE) return (EACCES); zs->zfetchstat_hits.value.ui64 = wmsum_value(&zfetch_sums.zfetchstat_hits); zs->zfetchstat_misses.value.ui64 = wmsum_value(&zfetch_sums.zfetchstat_misses); zs->zfetchstat_max_streams.value.ui64 = wmsum_value(&zfetch_sums.zfetchstat_max_streams); zs->zfetchstat_io_issued.value.ui64 = wmsum_value(&zfetch_sums.zfetchstat_io_issued); return (0); } void zfetch_init(void) { wmsum_init(&zfetch_sums.zfetchstat_hits, 0); wmsum_init(&zfetch_sums.zfetchstat_misses, 0); wmsum_init(&zfetch_sums.zfetchstat_max_streams, 0); wmsum_init(&zfetch_sums.zfetchstat_io_issued, 0); zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc", KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t), KSTAT_FLAG_VIRTUAL); if (zfetch_ksp != NULL) { zfetch_ksp->ks_data = &zfetch_stats; zfetch_ksp->ks_update = zfetch_kstats_update; kstat_install(zfetch_ksp); } } void zfetch_fini(void) { if (zfetch_ksp != NULL) { kstat_delete(zfetch_ksp); zfetch_ksp = NULL; } wmsum_fini(&zfetch_sums.zfetchstat_hits); wmsum_fini(&zfetch_sums.zfetchstat_misses); wmsum_fini(&zfetch_sums.zfetchstat_max_streams); wmsum_fini(&zfetch_sums.zfetchstat_io_issued); } /* * This takes a pointer to a zfetch structure and a dnode. It performs the * necessary setup for the zfetch structure, grokking data from the * associated dnode. */ void dmu_zfetch_init(zfetch_t *zf, dnode_t *dno) { if (zf == NULL) return; zf->zf_dnode = dno; zf->zf_numstreams = 0; list_create(&zf->zf_stream, sizeof (zstream_t), offsetof(zstream_t, zs_node)); mutex_init(&zf->zf_lock, NULL, MUTEX_DEFAULT, NULL); } static void dmu_zfetch_stream_fini(zstream_t *zs) { ASSERT(!list_link_active(&zs->zs_node)); zfs_refcount_destroy(&zs->zs_callers); zfs_refcount_destroy(&zs->zs_refs); kmem_free(zs, sizeof (*zs)); } static void dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs) { ASSERT(MUTEX_HELD(&zf->zf_lock)); list_remove(&zf->zf_stream, zs); zf->zf_numstreams--; membar_producer(); if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0) dmu_zfetch_stream_fini(zs); } /* * 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_fini(zfetch_t *zf) { zstream_t *zs; mutex_enter(&zf->zf_lock); while ((zs = list_head(&zf->zf_stream)) != NULL) dmu_zfetch_stream_remove(zf, zs); mutex_exit(&zf->zf_lock); list_destroy(&zf->zf_stream); mutex_destroy(&zf->zf_lock); zf->zf_dnode = NULL; } /* * 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 void dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid) { zstream_t *zs_next; hrtime_t now = gethrtime(); ASSERT(MUTEX_HELD(&zf->zf_lock)); /* * Clean up old streams. */ for (zstream_t *zs = list_head(&zf->zf_stream); zs != NULL; zs = zs_next) { zs_next = list_next(&zf->zf_stream, zs); /* * Skip if still active. 1 -- zf_stream reference. */ if (zfs_refcount_count(&zs->zs_refs) != 1) continue; if (((now - zs->zs_atime) / NANOSEC) > zfetch_min_sec_reap) dmu_zfetch_stream_remove(zf, zs); } /* * 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. */ uint32_t max_streams = MAX(1, MIN(zfetch_max_streams, zf->zf_dnode->dn_maxblkid * zf->zf_dnode->dn_datablksz / zfetch_max_distance)); if (zf->zf_numstreams >= max_streams) { ZFETCHSTAT_BUMP(zfetchstat_max_streams); return; } zstream_t *zs = kmem_zalloc(sizeof (*zs), KM_SLEEP); zs->zs_blkid = blkid; zs->zs_pf_blkid1 = blkid; zs->zs_pf_blkid = blkid; zs->zs_ipf_blkid1 = blkid; zs->zs_ipf_blkid = blkid; zs->zs_atime = now; zs->zs_fetch = zf; zs->zs_missed = B_FALSE; zfs_refcount_create(&zs->zs_callers); zfs_refcount_create(&zs->zs_refs); /* One reference for zf_stream. */ zfs_refcount_add(&zs->zs_refs, NULL); zf->zf_numstreams++; list_insert_head(&zf->zf_stream, zs); } static void dmu_zfetch_stream_done(void *arg, boolean_t io_issued) { (void) io_issued; zstream_t *zs = arg; if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0) dmu_zfetch_stream_fini(zs); } /* * This is the predictive prefetch entry point. dmu_zfetch_prepare() * associates dnode access specified with blkid and nblks arguments with * prefetch stream, predicts further accesses based on that stats and returns * the stream pointer on success. That pointer must later be passed to * dmu_zfetch_run() to initiate the speculative prefetch for the stream and * release it. dmu_zfetch() is a wrapper for simple cases when window between * prediction and prefetch initiation is not needed. * fetch_data argument specifies whether actual data blocks should be fetched: * FALSE -- prefetch only indirect blocks for predicted data blocks; * TRUE -- prefetch predicted data blocks plus following indirect blocks. */ zstream_t * dmu_zfetch_prepare(zfetch_t *zf, uint64_t blkid, uint64_t nblks, boolean_t fetch_data, boolean_t have_lock) { zstream_t *zs; int64_t pf_start, ipf_start; int64_t pf_ahead_blks, max_blks; int max_dist_blks, pf_nblks, ipf_nblks; uint64_t end_of_access_blkid, maxblkid; end_of_access_blkid = blkid + nblks; spa_t *spa = zf->zf_dnode->dn_objset->os_spa; if (zfs_prefetch_disable) return (NULL); /* * If we haven't yet loaded the indirect vdevs' mappings, we * can only read from blocks that we carefully ensure are on * concrete vdevs (or previously-loaded indirect vdevs). So we * can't allow the predictive prefetcher to attempt reads of other * blocks (e.g. of the MOS's dnode object). */ if (!spa_indirect_vdevs_loaded(spa)) return (NULL); /* * As a fast path for small (single-block) files, ignore access * to the first block. */ if (!have_lock && blkid == 0) return (NULL); if (!have_lock) rw_enter(&zf->zf_dnode->dn_struct_rwlock, RW_READER); /* * A fast path for small files for which no prefetch will * happen. */ maxblkid = zf->zf_dnode->dn_maxblkid; if (maxblkid < 2) { if (!have_lock) rw_exit(&zf->zf_dnode->dn_struct_rwlock); return (NULL); } mutex_enter(&zf->zf_lock); /* * Find matching prefetch stream. Depending on whether the accesses * are block-aligned, first block of the new access may either follow * the last block of the previous access, or be equal to it. */ for (zs = list_head(&zf->zf_stream); zs != NULL; zs = list_next(&zf->zf_stream, zs)) { if (blkid == zs->zs_blkid) { break; } else if (blkid + 1 == zs->zs_blkid) { blkid++; nblks--; break; } } /* * If the file is ending, remove the matching stream if found. * If not found then it is too late to create a new one now. */ if (end_of_access_blkid >= maxblkid) { if (zs != NULL) dmu_zfetch_stream_remove(zf, zs); mutex_exit(&zf->zf_lock); if (!have_lock) rw_exit(&zf->zf_dnode->dn_struct_rwlock); return (NULL); } /* Exit if we already prefetched this block before. */ if (nblks == 0) { mutex_exit(&zf->zf_lock); if (!have_lock) rw_exit(&zf->zf_dnode->dn_struct_rwlock); return (NULL); } if (zs == NULL) { /* * This access is not part of any existing stream. Create * a new stream for it. */ dmu_zfetch_stream_create(zf, end_of_access_blkid); mutex_exit(&zf->zf_lock); if (!have_lock) rw_exit(&zf->zf_dnode->dn_struct_rwlock); ZFETCHSTAT_BUMP(zfetchstat_misses); return (NULL); } /* * 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 the block we just accessed. In this case, * start just after the block we just accessed. */ pf_start = MAX(zs->zs_pf_blkid, end_of_access_blkid); if (zs->zs_pf_blkid1 < end_of_access_blkid) zs->zs_pf_blkid1 = end_of_access_blkid; if (zs->zs_ipf_blkid1 < end_of_access_blkid) zs->zs_ipf_blkid1 = end_of_access_blkid; /* * Double our amount of prefetched data, but don't let the * prefetch get further ahead than zfetch_max_distance. */ if (fetch_data) { max_dist_blks = zfetch_max_distance >> zf->zf_dnode->dn_datablkshift; /* * Previously, we were (zs_pf_blkid - blkid) ahead. We * want to now be double that, so read that amount again, * plus the amount we are catching up by (i.e. the amount * read just now). */ pf_ahead_blks = zs->zs_pf_blkid - blkid + nblks; max_blks = max_dist_blks - (pf_start - end_of_access_blkid); pf_nblks = MIN(pf_ahead_blks, max_blks); } else { pf_nblks = 0; } zs->zs_pf_blkid = pf_start + pf_nblks; /* * Do the same for indirects, starting from where we stopped last, * or where we will stop reading data blocks (and the indirects * that point to them). */ ipf_start = MAX(zs->zs_ipf_blkid, zs->zs_pf_blkid); max_dist_blks = zfetch_max_idistance >> zf->zf_dnode->dn_datablkshift; /* * We want to double our distance ahead of the data prefetch * (or reader, if we are not prefetching data). Previously, we * were (zs_ipf_blkid - blkid) ahead. To double that, we read * that amount again, plus the amount we are catching up by * (i.e. the amount read now + the amount of data prefetched now). */ pf_ahead_blks = zs->zs_ipf_blkid - blkid + nblks + pf_nblks; max_blks = max_dist_blks - (ipf_start - zs->zs_pf_blkid); ipf_nblks = MIN(pf_ahead_blks, max_blks); zs->zs_ipf_blkid = ipf_start + ipf_nblks; zs->zs_blkid = end_of_access_blkid; /* Protect the stream from reclamation. */ zs->zs_atime = gethrtime(); zfs_refcount_add(&zs->zs_refs, NULL); /* Count concurrent callers. */ zfs_refcount_add(&zs->zs_callers, NULL); mutex_exit(&zf->zf_lock); if (!have_lock) rw_exit(&zf->zf_dnode->dn_struct_rwlock); ZFETCHSTAT_BUMP(zfetchstat_hits); return (zs); } void dmu_zfetch_run(zstream_t *zs, boolean_t missed, boolean_t have_lock) { zfetch_t *zf = zs->zs_fetch; int64_t pf_start, pf_end, ipf_start, ipf_end; int epbs, issued; if (missed) zs->zs_missed = missed; /* * Postpone the prefetch if there are more concurrent callers. * It happens when multiple requests are waiting for the same * indirect block. The last one will run the prefetch for all. */ if (zfs_refcount_remove(&zs->zs_callers, NULL) != 0) { /* Drop reference taken in dmu_zfetch_prepare(). */ if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0) dmu_zfetch_stream_fini(zs); return; } mutex_enter(&zf->zf_lock); if (zs->zs_missed) { pf_start = zs->zs_pf_blkid1; pf_end = zs->zs_pf_blkid1 = zs->zs_pf_blkid; } else { pf_start = pf_end = 0; } ipf_start = MAX(zs->zs_pf_blkid1, zs->zs_ipf_blkid1); ipf_end = zs->zs_ipf_blkid1 = zs->zs_ipf_blkid; mutex_exit(&zf->zf_lock); ASSERT3S(pf_start, <=, pf_end); ASSERT3S(ipf_start, <=, ipf_end); epbs = zf->zf_dnode->dn_indblkshift - SPA_BLKPTRSHIFT; ipf_start = P2ROUNDUP(ipf_start, 1 << epbs) >> epbs; ipf_end = P2ROUNDUP(ipf_end, 1 << epbs) >> epbs; ASSERT3S(ipf_start, <=, ipf_end); issued = pf_end - pf_start + ipf_end - ipf_start; if (issued > 1) { /* More references on top of taken in dmu_zfetch_prepare(). */ for (int i = 0; i < issued - 1; i++) zfs_refcount_add(&zs->zs_refs, NULL); } else if (issued == 0) { /* Some other thread has done our work, so drop the ref. */ if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0) dmu_zfetch_stream_fini(zs); return; } if (!have_lock) rw_enter(&zf->zf_dnode->dn_struct_rwlock, RW_READER); issued = 0; for (int64_t blk = pf_start; blk < pf_end; blk++) { issued += dbuf_prefetch_impl(zf->zf_dnode, 0, blk, ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH, dmu_zfetch_stream_done, zs); } for (int64_t iblk = ipf_start; iblk < ipf_end; iblk++) { issued += dbuf_prefetch_impl(zf->zf_dnode, 1, iblk, ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH, dmu_zfetch_stream_done, zs); } if (!have_lock) rw_exit(&zf->zf_dnode->dn_struct_rwlock); if (issued) ZFETCHSTAT_ADD(zfetchstat_io_issued, issued); } void dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks, boolean_t fetch_data, boolean_t missed, boolean_t have_lock) { zstream_t *zs; zs = dmu_zfetch_prepare(zf, blkid, nblks, fetch_data, have_lock); if (zs) dmu_zfetch_run(zs, missed, have_lock); } ZFS_MODULE_PARAM(zfs_prefetch, zfs_prefetch_, disable, INT, ZMOD_RW, "Disable all ZFS prefetching"); ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_streams, UINT, ZMOD_RW, "Max number of streams per zfetch"); ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, min_sec_reap, UINT, ZMOD_RW, "Min time before stream reclaim"); ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_distance, UINT, ZMOD_RW, "Max bytes to prefetch per stream"); ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_idistance, UINT, ZMOD_RW, "Max bytes to prefetch indirects for per stream"); ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, array_rd_sz, ULONG, ZMOD_RW, "Number of bytes in a array_read");