| /* |
| * 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, 2015 by Delphix. All rights reserved. |
| */ |
| |
| #include <sys/zfs_context.h> |
| #include <sys/dnode.h> |
| #include <sys/dmu_objset.h> |
| #include <sys/dmu_zfetch.h> |
| #include <sys/dmu.h> |
| #include <sys/dbuf.h> |
| #include <sys/kstat.h> |
| |
| /* |
| * 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 = 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 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; |
| } zfetch_stats_t; |
| |
| static zfetch_stats_t zfetch_stats = { |
| { "hits", KSTAT_DATA_UINT64 }, |
| { "misses", KSTAT_DATA_UINT64 }, |
| { "max_streams", KSTAT_DATA_UINT64 }, |
| }; |
| |
| #define ZFETCHSTAT_BUMP(stat) \ |
| atomic_inc_64(&zfetch_stats.stat.value.ui64); |
| |
| kstat_t *zfetch_ksp; |
| |
| 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); |
| |
| if (zfetch_ksp != NULL) { |
| zfetch_ksp->ks_data = &zfetch_stats; |
| kstat_install(zfetch_ksp); |
| } |
| } |
| |
| void |
| zfetch_fini(void) |
| { |
| if (zfetch_ksp != NULL) { |
| kstat_delete(zfetch_ksp); |
| zfetch_ksp = NULL; |
| } |
| } |
| |
| /* |
| * 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; |
| |
| list_create(&zf->zf_stream, sizeof (zstream_t), |
| offsetof(zstream_t, zs_node)); |
| |
| rw_init(&zf->zf_rwlock, NULL, RW_DEFAULT, NULL); |
| } |
| |
| static void |
| dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs) |
| { |
| 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 (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; |
| |
| ASSERT(!RW_LOCK_HELD(&zf->zf_rwlock)); |
| |
| 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); |
| |
| 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; |
| int numstreams = 0; |
| |
| ASSERT(RW_WRITE_HELD(&zf->zf_rwlock)); |
| |
| /* |
| * 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); |
| if (((gethrtime() - zs->zs_atime) / NANOSEC) > |
| zfetch_min_sec_reap) |
| dmu_zfetch_stream_remove(zf, zs); |
| else |
| numstreams++; |
| } |
| |
| /* |
| * 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 (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_blkid = blkid; |
| zs->zs_ipf_blkid = blkid; |
| zs->zs_atime = gethrtime(); |
| mutex_init(&zs->zs_lock, NULL, MUTEX_DEFAULT, NULL); |
| |
| list_insert_head(&zf->zf_stream, zs); |
| } |
| |
| /* |
| * This is the predictive prefetch entry point. It associates dnode access |
| * specified with blkid and nblks arguments with prefetch stream, predicts |
| * further accesses based on that stats and initiates speculative prefetch. |
| * 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. |
| */ |
| void |
| dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks, boolean_t fetch_data) |
| { |
| zstream_t *zs; |
| int64_t pf_start, ipf_start, ipf_istart, ipf_iend; |
| int64_t pf_ahead_blks, max_blks; |
| int epbs, max_dist_blks, pf_nblks, ipf_nblks; |
| uint64_t end_of_access_blkid; |
| end_of_access_blkid = blkid + nblks; |
| spa_t *spa = zf->zf_dnode->dn_objset->os_spa; |
| krw_t rw = RW_READER; |
| |
| if (zfs_prefetch_disable) |
| return; |
| /* |
| * 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; |
| |
| /* |
| * As a fast path for small (single-block) files, ignore access |
| * to the first block. |
| */ |
| if (blkid == 0) |
| return; |
| |
| retry: |
| rw_enter(&zf->zf_rwlock, rw); |
| |
| /* |
| * 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 || blkid + 1 == 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) { |
| break; |
| } else if (blkid + 1 == zs->zs_blkid) { |
| blkid++; |
| nblks--; |
| if (nblks == 0) { |
| /* Already prefetched this before. */ |
| mutex_exit(&zs->zs_lock); |
| rw_exit(&zf->zf_rwlock); |
| return; |
| } |
| break; |
| } |
| mutex_exit(&zs->zs_lock); |
| } |
| } |
| |
| if (zs == NULL) { |
| /* |
| * This access is not part of any existing stream. Create |
| * a new stream for it. |
| */ |
| ZFETCHSTAT_BUMP(zfetchstat_misses); |
| if (rw == RW_READER && !rw_tryupgrade(&zf->zf_rwlock)) { |
| rw_exit(&zf->zf_rwlock); |
| rw = RW_WRITER; |
| goto retry; |
| } |
| |
| dmu_zfetch_stream_create(zf, end_of_access_blkid); |
| rw_exit(&zf->zf_rwlock); |
| return; |
| } |
| |
| /* |
| * 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); |
| |
| /* |
| * 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 - end_of_access_blkid); |
| ipf_nblks = MIN(pf_ahead_blks, max_blks); |
| zs->zs_ipf_blkid = ipf_start + ipf_nblks; |
| |
| epbs = zf->zf_dnode->dn_indblkshift - SPA_BLKPTRSHIFT; |
| ipf_istart = P2ROUNDUP(ipf_start, 1 << epbs) >> epbs; |
| ipf_iend = P2ROUNDUP(zs->zs_ipf_blkid, 1 << epbs) >> epbs; |
| |
| zs->zs_atime = gethrtime(); |
| zs->zs_blkid = end_of_access_blkid; |
| mutex_exit(&zs->zs_lock); |
| rw_exit(&zf->zf_rwlock); |
| |
| /* |
| * dbuf_prefetch() is asynchronous (even when it needs to read |
| * indirect blocks), but we still prefer to drop our locks before |
| * calling it to reduce the time we hold them. |
| */ |
| |
| for (int i = 0; i < pf_nblks; i++) { |
| dbuf_prefetch(zf->zf_dnode, 0, pf_start + i, |
| ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH); |
| } |
| for (int64_t iblk = ipf_istart; iblk < ipf_iend; iblk++) { |
| dbuf_prefetch(zf->zf_dnode, 1, iblk, |
| ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH); |
| } |
| ZFETCHSTAT_BUMP(zfetchstat_hits); |
| } |
| |
| #if defined(_KERNEL) |
| /* BEGIN CSTYLED */ |
| module_param(zfs_prefetch_disable, int, 0644); |
| MODULE_PARM_DESC(zfs_prefetch_disable, "Disable all ZFS prefetching"); |
| |
| module_param(zfetch_max_streams, uint, 0644); |
| 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_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"); |
| /* END CSTYLED */ |
| #endif |