/* * 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 https://opensource.org/licenses/CDDL-1.0. * 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 #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 = 1; /* max time before stream delete */ static unsigned int zfetch_max_sec_reap = 2; /* min bytes to prefetch per stream (default 4MB) */ static unsigned int zfetch_min_distance = 4 * 1024 * 1024; /* max bytes to prefetch per stream (default 64MB) */ unsigned int zfetch_max_distance = 64 * 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) */ uint64_t 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; kstat_named_t zfetchstat_io_active; } 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 }, { "io_active", KSTAT_DATA_UINT64 }, }; struct { wmsum_t zfetchstat_hits; wmsum_t zfetchstat_misses; wmsum_t zfetchstat_max_streams; wmsum_t zfetchstat_io_issued; aggsum_t zfetchstat_io_active; } 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); zs->zfetchstat_io_active.value.ui64 = aggsum_value(&zfetch_sums.zfetchstat_io_active); 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); aggsum_init(&zfetch_sums.zfetchstat_io_active, 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); ASSERT0(aggsum_value(&zfetch_sums.zfetchstat_io_active)); aggsum_fini(&zfetch_sums.zfetchstat_io_active); } /* * 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 active streams already, create one more. * In process delete/reuse all streams without hits for zfetch_max_sec_reap. * If needed, reuse oldest stream without hits for zfetch_min_sec_reap or ever. * The "blkid" argument is the next block that we expect this stream to access. */ static void dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid) { zstream_t *zs, *zs_next, *zs_old = NULL; hrtime_t now = gethrtime(), t; ASSERT(MUTEX_HELD(&zf->zf_lock)); /* * Delete too old streams, reusing the first found one. */ t = now - SEC2NSEC(zfetch_max_sec_reap); for (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 (zs->zs_atime > t) continue; if (zs_old) dmu_zfetch_stream_remove(zf, zs); else zs_old = zs; } if (zs_old) { zs = zs_old; goto reuse; } /* * 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. */ 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) { t = now - SEC2NSEC(zfetch_min_sec_reap); for (zs = list_head(&zf->zf_stream); zs != NULL; zs = list_next(&zf->zf_stream, zs)) { if (zfs_refcount_count(&zs->zs_refs) != 1) continue; if (zs->zs_atime > t) continue; if (zs_old == NULL || zs->zs_atime < zs_old->zs_atime) zs_old = zs; } if (zs_old) { zs = zs_old; goto reuse; } ZFETCHSTAT_BUMP(zfetchstat_max_streams); return; } zs = kmem_zalloc(sizeof (*zs), KM_SLEEP); zs->zs_fetch = zf; 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); reuse: zs->zs_blkid = blkid; zs->zs_pf_dist = 0; zs->zs_pf_start = blkid; zs->zs_pf_end = blkid; zs->zs_ipf_dist = 0; zs->zs_ipf_start = blkid; zs->zs_ipf_end = blkid; /* Allow immediate stream reuse until first hit. */ zs->zs_atime = now - SEC2NSEC(zfetch_min_sec_reap); zs->zs_missed = B_FALSE; zs->zs_more = B_FALSE; } static void dmu_zfetch_done(void *arg, uint64_t level, uint64_t blkid, boolean_t io_issued) { zstream_t *zs = arg; if (io_issued && level == 0 && blkid < zs->zs_blkid) zs->zs_more = B_TRUE; if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0) dmu_zfetch_stream_fini(zs); aggsum_add(&zfetch_sums.zfetchstat_io_active, -1); } /* * 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; 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. */ uint64_t 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. */ uint64_t end_of_access_blkid = blkid + nblks; 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. Calculate further prefetch distances. * * Start prefetch from the demand access size (nblks). Double the * distance every access up to zfetch_min_distance. After that only * if needed increase the distance by 1/8 up to zfetch_max_distance. * * Don't double the distance beyond single block if we have more * than ~6% of ARC held by active prefetches. It should help with * getting out of RAM on some badly mispredicted read patterns. */ unsigned int dbs = zf->zf_dnode->dn_datablkshift; unsigned int nbytes = nblks << dbs; unsigned int pf_nblks; if (fetch_data) { if (unlikely(zs->zs_pf_dist < nbytes)) zs->zs_pf_dist = nbytes; else if (zs->zs_pf_dist < zfetch_min_distance && (zs->zs_pf_dist < (1 << dbs) || aggsum_compare(&zfetch_sums.zfetchstat_io_active, arc_c_max >> (4 + dbs)) < 0)) zs->zs_pf_dist *= 2; else if (zs->zs_more) zs->zs_pf_dist += zs->zs_pf_dist / 8; zs->zs_more = B_FALSE; if (zs->zs_pf_dist > zfetch_max_distance) zs->zs_pf_dist = zfetch_max_distance; pf_nblks = zs->zs_pf_dist >> dbs; } else { pf_nblks = 0; } if (zs->zs_pf_start < end_of_access_blkid) zs->zs_pf_start = end_of_access_blkid; if (zs->zs_pf_end < end_of_access_blkid + pf_nblks) zs->zs_pf_end = end_of_access_blkid + pf_nblks; /* * Do the same for indirects, starting where we will stop reading * data blocks (and the indirects that point to them). */ if (unlikely(zs->zs_ipf_dist < nbytes)) zs->zs_ipf_dist = nbytes; else zs->zs_ipf_dist *= 2; if (zs->zs_ipf_dist > zfetch_max_idistance) zs->zs_ipf_dist = zfetch_max_idistance; pf_nblks = zs->zs_ipf_dist >> dbs; if (zs->zs_ipf_start < zs->zs_pf_end) zs->zs_ipf_start = zs->zs_pf_end; if (zs->zs_ipf_end < zs->zs_pf_end + pf_nblks) zs->zs_ipf_end = zs->zs_pf_end + pf_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_start; pf_end = zs->zs_pf_start = zs->zs_pf_end; } else { pf_start = pf_end = 0; } ipf_start = zs->zs_ipf_start; ipf_end = zs->zs_ipf_start = zs->zs_ipf_end; 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; } aggsum_add(&zfetch_sums.zfetchstat_io_active, issued); 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, 0, dmu_zfetch_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, 0, dmu_zfetch_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_sec_reap, UINT, ZMOD_RW, "Max time before stream delete"); ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, min_distance, UINT, ZMOD_RW, "Min bytes to prefetch per stream"); 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, U64, ZMOD_RW, "Number of bytes in a array_read");