| /* |
| * 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, 2016 by Delphix. All rights reserved. |
| */ |
| |
| #include <sys/zfs_context.h> |
| #include <sys/spa.h> |
| #include <sys/vdev_impl.h> |
| #include <sys/zio.h> |
| #include <sys/kstat.h> |
| #include <sys/abd.h> |
| |
| /* |
| * Virtual device read-ahead caching. |
| * |
| * This file implements a simple LRU read-ahead cache. When the DMU reads |
| * a given block, it will often want other, nearby blocks soon thereafter. |
| * We take advantage of this by reading a larger disk region and caching |
| * the result. In the best case, this can turn 128 back-to-back 512-byte |
| * reads into a single 64k read followed by 127 cache hits; this reduces |
| * latency dramatically. In the worst case, it can turn an isolated 512-byte |
| * read into a 64k read, which doesn't affect latency all that much but is |
| * terribly wasteful of bandwidth. A more intelligent version of the cache |
| * could keep track of access patterns and not do read-ahead unless it sees |
| * at least two temporally close I/Os to the same region. Currently, only |
| * metadata I/O is inflated. A further enhancement could take advantage of |
| * more semantic information about the I/O. And it could use something |
| * faster than an AVL tree; that was chosen solely for convenience. |
| * |
| * There are five cache operations: allocate, fill, read, write, evict. |
| * |
| * (1) Allocate. This reserves a cache entry for the specified region. |
| * We separate the allocate and fill operations so that multiple threads |
| * don't generate I/O for the same cache miss. |
| * |
| * (2) Fill. When the I/O for a cache miss completes, the fill routine |
| * places the data in the previously allocated cache entry. |
| * |
| * (3) Read. Read data from the cache. |
| * |
| * (4) Write. Update cache contents after write completion. |
| * |
| * (5) Evict. When allocating a new entry, we evict the oldest (LRU) entry |
| * if the total cache size exceeds zfs_vdev_cache_size. |
| */ |
| |
| /* |
| * These tunables are for performance analysis. |
| */ |
| /* |
| * All i/os smaller than zfs_vdev_cache_max will be turned into |
| * 1<<zfs_vdev_cache_bshift byte reads by the vdev_cache (aka software |
| * track buffer). At most zfs_vdev_cache_size bytes will be kept in each |
| * vdev's vdev_cache. |
| * |
| * TODO: Note that with the current ZFS code, it turns out that the |
| * vdev cache is not helpful, and in some cases actually harmful. It |
| * is better if we disable this. Once some time has passed, we should |
| * actually remove this to simplify the code. For now we just disable |
| * it by setting the zfs_vdev_cache_size to zero. Note that Solaris 11 |
| * has made these same changes. |
| */ |
| int zfs_vdev_cache_max = 1<<14; /* 16KB */ |
| int zfs_vdev_cache_size = 0; |
| int zfs_vdev_cache_bshift = 16; |
| |
| #define VCBS (1 << zfs_vdev_cache_bshift) /* 64KB */ |
| |
| kstat_t *vdc_ksp = NULL; |
| |
| typedef struct vdc_stats { |
| kstat_named_t vdc_stat_delegations; |
| kstat_named_t vdc_stat_hits; |
| kstat_named_t vdc_stat_misses; |
| } vdc_stats_t; |
| |
| static vdc_stats_t vdc_stats = { |
| { "delegations", KSTAT_DATA_UINT64 }, |
| { "hits", KSTAT_DATA_UINT64 }, |
| { "misses", KSTAT_DATA_UINT64 } |
| }; |
| |
| #define VDCSTAT_BUMP(stat) atomic_inc_64(&vdc_stats.stat.value.ui64); |
| |
| static inline int |
| vdev_cache_offset_compare(const void *a1, const void *a2) |
| { |
| const vdev_cache_entry_t *ve1 = (const vdev_cache_entry_t *)a1; |
| const vdev_cache_entry_t *ve2 = (const vdev_cache_entry_t *)a2; |
| |
| return (AVL_CMP(ve1->ve_offset, ve2->ve_offset)); |
| } |
| |
| static int |
| vdev_cache_lastused_compare(const void *a1, const void *a2) |
| { |
| const vdev_cache_entry_t *ve1 = (const vdev_cache_entry_t *)a1; |
| const vdev_cache_entry_t *ve2 = (const vdev_cache_entry_t *)a2; |
| |
| int cmp = AVL_CMP(ve1->ve_lastused, ve2->ve_lastused); |
| if (likely(cmp)) |
| return (cmp); |
| |
| /* |
| * Among equally old entries, sort by offset to ensure uniqueness. |
| */ |
| return (vdev_cache_offset_compare(a1, a2)); |
| } |
| |
| /* |
| * Evict the specified entry from the cache. |
| */ |
| static void |
| vdev_cache_evict(vdev_cache_t *vc, vdev_cache_entry_t *ve) |
| { |
| ASSERT(MUTEX_HELD(&vc->vc_lock)); |
| ASSERT3P(ve->ve_fill_io, ==, NULL); |
| ASSERT3P(ve->ve_abd, !=, NULL); |
| |
| avl_remove(&vc->vc_lastused_tree, ve); |
| avl_remove(&vc->vc_offset_tree, ve); |
| abd_free(ve->ve_abd); |
| kmem_free(ve, sizeof (vdev_cache_entry_t)); |
| } |
| |
| /* |
| * Allocate an entry in the cache. At the point we don't have the data, |
| * we're just creating a placeholder so that multiple threads don't all |
| * go off and read the same blocks. |
| */ |
| static vdev_cache_entry_t * |
| vdev_cache_allocate(zio_t *zio) |
| { |
| vdev_cache_t *vc = &zio->io_vd->vdev_cache; |
| uint64_t offset = P2ALIGN(zio->io_offset, VCBS); |
| vdev_cache_entry_t *ve; |
| |
| ASSERT(MUTEX_HELD(&vc->vc_lock)); |
| |
| if (zfs_vdev_cache_size == 0) |
| return (NULL); |
| |
| /* |
| * If adding a new entry would exceed the cache size, |
| * evict the oldest entry (LRU). |
| */ |
| if ((avl_numnodes(&vc->vc_lastused_tree) << zfs_vdev_cache_bshift) > |
| zfs_vdev_cache_size) { |
| ve = avl_first(&vc->vc_lastused_tree); |
| if (ve->ve_fill_io != NULL) |
| return (NULL); |
| ASSERT3U(ve->ve_hits, !=, 0); |
| vdev_cache_evict(vc, ve); |
| } |
| |
| ve = kmem_zalloc(sizeof (vdev_cache_entry_t), KM_SLEEP); |
| ve->ve_offset = offset; |
| ve->ve_lastused = ddi_get_lbolt(); |
| ve->ve_abd = abd_alloc_for_io(VCBS, B_TRUE); |
| |
| avl_add(&vc->vc_offset_tree, ve); |
| avl_add(&vc->vc_lastused_tree, ve); |
| |
| return (ve); |
| } |
| |
| static void |
| vdev_cache_hit(vdev_cache_t *vc, vdev_cache_entry_t *ve, zio_t *zio) |
| { |
| uint64_t cache_phase = P2PHASE(zio->io_offset, VCBS); |
| |
| ASSERT(MUTEX_HELD(&vc->vc_lock)); |
| ASSERT3P(ve->ve_fill_io, ==, NULL); |
| |
| if (ve->ve_lastused != ddi_get_lbolt()) { |
| avl_remove(&vc->vc_lastused_tree, ve); |
| ve->ve_lastused = ddi_get_lbolt(); |
| avl_add(&vc->vc_lastused_tree, ve); |
| } |
| |
| ve->ve_hits++; |
| abd_copy_off(zio->io_abd, ve->ve_abd, 0, cache_phase, zio->io_size); |
| } |
| |
| /* |
| * Fill a previously allocated cache entry with data. |
| */ |
| static void |
| vdev_cache_fill(zio_t *fio) |
| { |
| vdev_t *vd = fio->io_vd; |
| vdev_cache_t *vc = &vd->vdev_cache; |
| vdev_cache_entry_t *ve = fio->io_private; |
| zio_t *pio; |
| |
| ASSERT3U(fio->io_size, ==, VCBS); |
| |
| /* |
| * Add data to the cache. |
| */ |
| mutex_enter(&vc->vc_lock); |
| |
| ASSERT3P(ve->ve_fill_io, ==, fio); |
| ASSERT3U(ve->ve_offset, ==, fio->io_offset); |
| ASSERT3P(ve->ve_abd, ==, fio->io_abd); |
| |
| ve->ve_fill_io = NULL; |
| |
| /* |
| * Even if this cache line was invalidated by a missed write update, |
| * any reads that were queued up before the missed update are still |
| * valid, so we can satisfy them from this line before we evict it. |
| */ |
| zio_link_t *zl = NULL; |
| while ((pio = zio_walk_parents(fio, &zl)) != NULL) |
| vdev_cache_hit(vc, ve, pio); |
| |
| if (fio->io_error || ve->ve_missed_update) |
| vdev_cache_evict(vc, ve); |
| |
| mutex_exit(&vc->vc_lock); |
| } |
| |
| /* |
| * Read data from the cache. Returns B_TRUE cache hit, B_FALSE on miss. |
| */ |
| boolean_t |
| vdev_cache_read(zio_t *zio) |
| { |
| vdev_cache_t *vc = &zio->io_vd->vdev_cache; |
| vdev_cache_entry_t *ve, *ve_search; |
| uint64_t cache_offset = P2ALIGN(zio->io_offset, VCBS); |
| zio_t *fio; |
| ASSERTV(uint64_t cache_phase = P2PHASE(zio->io_offset, VCBS)); |
| |
| ASSERT3U(zio->io_type, ==, ZIO_TYPE_READ); |
| |
| if (zio->io_flags & ZIO_FLAG_DONT_CACHE) |
| return (B_FALSE); |
| |
| if (zio->io_size > zfs_vdev_cache_max) |
| return (B_FALSE); |
| |
| /* |
| * If the I/O straddles two or more cache blocks, don't cache it. |
| */ |
| if (P2BOUNDARY(zio->io_offset, zio->io_size, VCBS)) |
| return (B_FALSE); |
| |
| ASSERT3U(cache_phase + zio->io_size, <=, VCBS); |
| |
| mutex_enter(&vc->vc_lock); |
| |
| ve_search = kmem_alloc(sizeof (vdev_cache_entry_t), KM_SLEEP); |
| ve_search->ve_offset = cache_offset; |
| ve = avl_find(&vc->vc_offset_tree, ve_search, NULL); |
| kmem_free(ve_search, sizeof (vdev_cache_entry_t)); |
| |
| if (ve != NULL) { |
| if (ve->ve_missed_update) { |
| mutex_exit(&vc->vc_lock); |
| return (B_FALSE); |
| } |
| |
| if ((fio = ve->ve_fill_io) != NULL) { |
| zio_vdev_io_bypass(zio); |
| zio_add_child(zio, fio); |
| mutex_exit(&vc->vc_lock); |
| VDCSTAT_BUMP(vdc_stat_delegations); |
| return (B_TRUE); |
| } |
| |
| vdev_cache_hit(vc, ve, zio); |
| zio_vdev_io_bypass(zio); |
| |
| mutex_exit(&vc->vc_lock); |
| VDCSTAT_BUMP(vdc_stat_hits); |
| return (B_TRUE); |
| } |
| |
| ve = vdev_cache_allocate(zio); |
| |
| if (ve == NULL) { |
| mutex_exit(&vc->vc_lock); |
| return (B_FALSE); |
| } |
| |
| fio = zio_vdev_delegated_io(zio->io_vd, cache_offset, |
| ve->ve_abd, VCBS, ZIO_TYPE_READ, ZIO_PRIORITY_NOW, |
| ZIO_FLAG_DONT_CACHE, vdev_cache_fill, ve); |
| |
| ve->ve_fill_io = fio; |
| zio_vdev_io_bypass(zio); |
| zio_add_child(zio, fio); |
| |
| mutex_exit(&vc->vc_lock); |
| zio_nowait(fio); |
| VDCSTAT_BUMP(vdc_stat_misses); |
| |
| return (B_TRUE); |
| } |
| |
| /* |
| * Update cache contents upon write completion. |
| */ |
| void |
| vdev_cache_write(zio_t *zio) |
| { |
| vdev_cache_t *vc = &zio->io_vd->vdev_cache; |
| vdev_cache_entry_t *ve, ve_search; |
| uint64_t io_start = zio->io_offset; |
| uint64_t io_end = io_start + zio->io_size; |
| uint64_t min_offset = P2ALIGN(io_start, VCBS); |
| uint64_t max_offset = P2ROUNDUP(io_end, VCBS); |
| avl_index_t where; |
| |
| ASSERT3U(zio->io_type, ==, ZIO_TYPE_WRITE); |
| |
| mutex_enter(&vc->vc_lock); |
| |
| ve_search.ve_offset = min_offset; |
| ve = avl_find(&vc->vc_offset_tree, &ve_search, &where); |
| |
| if (ve == NULL) |
| ve = avl_nearest(&vc->vc_offset_tree, where, AVL_AFTER); |
| |
| while (ve != NULL && ve->ve_offset < max_offset) { |
| uint64_t start = MAX(ve->ve_offset, io_start); |
| uint64_t end = MIN(ve->ve_offset + VCBS, io_end); |
| |
| if (ve->ve_fill_io != NULL) { |
| ve->ve_missed_update = 1; |
| } else { |
| abd_copy_off(ve->ve_abd, zio->io_abd, |
| start - ve->ve_offset, start - io_start, |
| end - start); |
| } |
| ve = AVL_NEXT(&vc->vc_offset_tree, ve); |
| } |
| mutex_exit(&vc->vc_lock); |
| } |
| |
| void |
| vdev_cache_purge(vdev_t *vd) |
| { |
| vdev_cache_t *vc = &vd->vdev_cache; |
| vdev_cache_entry_t *ve; |
| |
| mutex_enter(&vc->vc_lock); |
| while ((ve = avl_first(&vc->vc_offset_tree)) != NULL) |
| vdev_cache_evict(vc, ve); |
| mutex_exit(&vc->vc_lock); |
| } |
| |
| void |
| vdev_cache_init(vdev_t *vd) |
| { |
| vdev_cache_t *vc = &vd->vdev_cache; |
| |
| mutex_init(&vc->vc_lock, NULL, MUTEX_DEFAULT, NULL); |
| |
| avl_create(&vc->vc_offset_tree, vdev_cache_offset_compare, |
| sizeof (vdev_cache_entry_t), |
| offsetof(struct vdev_cache_entry, ve_offset_node)); |
| |
| avl_create(&vc->vc_lastused_tree, vdev_cache_lastused_compare, |
| sizeof (vdev_cache_entry_t), |
| offsetof(struct vdev_cache_entry, ve_lastused_node)); |
| } |
| |
| void |
| vdev_cache_fini(vdev_t *vd) |
| { |
| vdev_cache_t *vc = &vd->vdev_cache; |
| |
| vdev_cache_purge(vd); |
| |
| avl_destroy(&vc->vc_offset_tree); |
| avl_destroy(&vc->vc_lastused_tree); |
| |
| mutex_destroy(&vc->vc_lock); |
| } |
| |
| void |
| vdev_cache_stat_init(void) |
| { |
| vdc_ksp = kstat_create("zfs", 0, "vdev_cache_stats", "misc", |
| KSTAT_TYPE_NAMED, sizeof (vdc_stats) / sizeof (kstat_named_t), |
| KSTAT_FLAG_VIRTUAL); |
| if (vdc_ksp != NULL) { |
| vdc_ksp->ks_data = &vdc_stats; |
| kstat_install(vdc_ksp); |
| } |
| } |
| |
| void |
| vdev_cache_stat_fini(void) |
| { |
| if (vdc_ksp != NULL) { |
| kstat_delete(vdc_ksp); |
| vdc_ksp = NULL; |
| } |
| } |
| |
| #if defined(_KERNEL) |
| module_param(zfs_vdev_cache_max, int, 0644); |
| MODULE_PARM_DESC(zfs_vdev_cache_max, "Inflate reads small than max"); |
| |
| module_param(zfs_vdev_cache_size, int, 0444); |
| MODULE_PARM_DESC(zfs_vdev_cache_size, "Total size of the per-disk cache"); |
| |
| module_param(zfs_vdev_cache_bshift, int, 0644); |
| MODULE_PARM_DESC(zfs_vdev_cache_bshift, "Shift size to inflate reads too"); |
| #endif |