--- /dev/null
+/*
+ * 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
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