/* * 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 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> /* * 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 futher 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_add_64(&vdc_stats.stat.value.ui64, 1); static int vdev_cache_offset_compare(const void *a1, const void *a2) { const vdev_cache_entry_t *ve1 = a1; const vdev_cache_entry_t *ve2 = a2; if (ve1->ve_offset < ve2->ve_offset) return (-1); if (ve1->ve_offset > ve2->ve_offset) return (1); return (0); } static int vdev_cache_lastused_compare(const void *a1, const void *a2) { const vdev_cache_entry_t *ve1 = a1; const vdev_cache_entry_t *ve2 = a2; if (ddi_time_before(ve1->ve_lastused, ve2->ve_lastused)) return (-1); if (ddi_time_after(ve1->ve_lastused, ve2->ve_lastused)) return (1); /* * 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)); ASSERT(ve->ve_fill_io == NULL); ASSERT(ve->ve_data != NULL); avl_remove(&vc->vc_lastused_tree, ve); avl_remove(&vc->vc_offset_tree, ve); zio_buf_free(ve->ve_data, VCBS); 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); ASSERT(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_data = zio_buf_alloc(VCBS); 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)); ASSERT(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++; bcopy(ve->ve_data + cache_phase, zio->io_data, 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; ASSERT(fio->io_size == VCBS); /* * Add data to the cache. */ mutex_enter(&vc->vc_lock); ASSERT(ve->ve_fill_io == fio); ASSERT(ve->ve_offset == fio->io_offset); ASSERT(ve->ve_data == fio->io_data); 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. */ while ((pio = zio_walk_parents(fio)) != 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)); ASSERT(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); ASSERT(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_data, 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; ASSERT(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 { bcopy((char *)zio->io_data + start - io_start, ve->ve_data + start - ve->ve_offset, 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) && defined(HAVE_SPL) 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