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-rw-r--r--uts/common/fs/zfs/dmu_zfetch.c724
1 files changed, 724 insertions, 0 deletions
diff --git a/uts/common/fs/zfs/dmu_zfetch.c b/uts/common/fs/zfs/dmu_zfetch.c
new file mode 100644
index 000000000000..37037c30f623
--- /dev/null
+++ b/uts/common/fs/zfs/dmu_zfetch.c
@@ -0,0 +1,724 @@
+/*
+ * 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.
+ */
+
+#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>
+
+/*
+ * I'm against tune-ables, but these should probably exist as tweakable globals
+ * until we can get this working the way we want it to.
+ */
+
+int zfs_prefetch_disable = 0;
+
+/* max # of streams per zfetch */
+uint32_t zfetch_max_streams = 8;
+/* min time before stream reclaim */
+uint32_t zfetch_min_sec_reap = 2;
+/* max number of blocks to fetch at a time */
+uint32_t zfetch_block_cap = 256;
+/* number of bytes in a array_read at which we stop prefetching (1Mb) */
+uint64_t zfetch_array_rd_sz = 1024 * 1024;
+
+/* forward decls for static routines */
+static int dmu_zfetch_colinear(zfetch_t *, zstream_t *);
+static void dmu_zfetch_dofetch(zfetch_t *, zstream_t *);
+static uint64_t dmu_zfetch_fetch(dnode_t *, uint64_t, uint64_t);
+static uint64_t dmu_zfetch_fetchsz(dnode_t *, uint64_t, uint64_t);
+static int dmu_zfetch_find(zfetch_t *, zstream_t *, int);
+static int dmu_zfetch_stream_insert(zfetch_t *, zstream_t *);
+static zstream_t *dmu_zfetch_stream_reclaim(zfetch_t *);
+static void dmu_zfetch_stream_remove(zfetch_t *, zstream_t *);
+static int dmu_zfetch_streams_equal(zstream_t *, zstream_t *);
+
+typedef struct zfetch_stats {
+ kstat_named_t zfetchstat_hits;
+ kstat_named_t zfetchstat_misses;
+ kstat_named_t zfetchstat_colinear_hits;
+ kstat_named_t zfetchstat_colinear_misses;
+ kstat_named_t zfetchstat_stride_hits;
+ kstat_named_t zfetchstat_stride_misses;
+ kstat_named_t zfetchstat_reclaim_successes;
+ kstat_named_t zfetchstat_reclaim_failures;
+ kstat_named_t zfetchstat_stream_resets;
+ kstat_named_t zfetchstat_stream_noresets;
+ kstat_named_t zfetchstat_bogus_streams;
+} zfetch_stats_t;
+
+static zfetch_stats_t zfetch_stats = {
+ { "hits", KSTAT_DATA_UINT64 },
+ { "misses", KSTAT_DATA_UINT64 },
+ { "colinear_hits", KSTAT_DATA_UINT64 },
+ { "colinear_misses", KSTAT_DATA_UINT64 },
+ { "stride_hits", KSTAT_DATA_UINT64 },
+ { "stride_misses", KSTAT_DATA_UINT64 },
+ { "reclaim_successes", KSTAT_DATA_UINT64 },
+ { "reclaim_failures", KSTAT_DATA_UINT64 },
+ { "streams_resets", KSTAT_DATA_UINT64 },
+ { "streams_noresets", KSTAT_DATA_UINT64 },
+ { "bogus_streams", KSTAT_DATA_UINT64 },
+};
+
+#define ZFETCHSTAT_INCR(stat, val) \
+ atomic_add_64(&zfetch_stats.stat.value.ui64, (val));
+
+#define ZFETCHSTAT_BUMP(stat) ZFETCHSTAT_INCR(stat, 1);
+
+kstat_t *zfetch_ksp;
+
+/*
+ * Given a zfetch structure and a zstream structure, determine whether the
+ * blocks to be read are part of a co-linear pair of existing prefetch
+ * streams. If a set is found, coalesce the streams, removing one, and
+ * configure the prefetch so it looks for a strided access pattern.
+ *
+ * In other words: if we find two sequential access streams that are
+ * the same length and distance N appart, and this read is N from the
+ * last stream, then we are probably in a strided access pattern. So
+ * combine the two sequential streams into a single strided stream.
+ *
+ * If no co-linear streams are found, return NULL.
+ */
+static int
+dmu_zfetch_colinear(zfetch_t *zf, zstream_t *zh)
+{
+ zstream_t *z_walk;
+ zstream_t *z_comp;
+
+ if (! rw_tryenter(&zf->zf_rwlock, RW_WRITER))
+ return (0);
+
+ if (zh == NULL) {
+ rw_exit(&zf->zf_rwlock);
+ return (0);
+ }
+
+ for (z_walk = list_head(&zf->zf_stream); z_walk;
+ z_walk = list_next(&zf->zf_stream, z_walk)) {
+ for (z_comp = list_next(&zf->zf_stream, z_walk); z_comp;
+ z_comp = list_next(&zf->zf_stream, z_comp)) {
+ int64_t diff;
+
+ if (z_walk->zst_len != z_walk->zst_stride ||
+ z_comp->zst_len != z_comp->zst_stride) {
+ continue;
+ }
+
+ diff = z_comp->zst_offset - z_walk->zst_offset;
+ if (z_comp->zst_offset + diff == zh->zst_offset) {
+ z_walk->zst_offset = zh->zst_offset;
+ z_walk->zst_direction = diff < 0 ? -1 : 1;
+ z_walk->zst_stride =
+ diff * z_walk->zst_direction;
+ z_walk->zst_ph_offset =
+ zh->zst_offset + z_walk->zst_stride;
+ dmu_zfetch_stream_remove(zf, z_comp);
+ mutex_destroy(&z_comp->zst_lock);
+ kmem_free(z_comp, sizeof (zstream_t));
+
+ dmu_zfetch_dofetch(zf, z_walk);
+
+ rw_exit(&zf->zf_rwlock);
+ return (1);
+ }
+
+ diff = z_walk->zst_offset - z_comp->zst_offset;
+ if (z_walk->zst_offset + diff == zh->zst_offset) {
+ z_walk->zst_offset = zh->zst_offset;
+ z_walk->zst_direction = diff < 0 ? -1 : 1;
+ z_walk->zst_stride =
+ diff * z_walk->zst_direction;
+ z_walk->zst_ph_offset =
+ zh->zst_offset + z_walk->zst_stride;
+ dmu_zfetch_stream_remove(zf, z_comp);
+ mutex_destroy(&z_comp->zst_lock);
+ kmem_free(z_comp, sizeof (zstream_t));
+
+ dmu_zfetch_dofetch(zf, z_walk);
+
+ rw_exit(&zf->zf_rwlock);
+ return (1);
+ }
+ }
+ }
+
+ rw_exit(&zf->zf_rwlock);
+ return (0);
+}
+
+/*
+ * Given a zstream_t, determine the bounds of the prefetch. Then call the
+ * routine that actually prefetches the individual blocks.
+ */
+static void
+dmu_zfetch_dofetch(zfetch_t *zf, zstream_t *zs)
+{
+ uint64_t prefetch_tail;
+ uint64_t prefetch_limit;
+ uint64_t prefetch_ofst;
+ uint64_t prefetch_len;
+ uint64_t blocks_fetched;
+
+ zs->zst_stride = MAX((int64_t)zs->zst_stride, zs->zst_len);
+ zs->zst_cap = MIN(zfetch_block_cap, 2 * zs->zst_cap);
+
+ prefetch_tail = MAX((int64_t)zs->zst_ph_offset,
+ (int64_t)(zs->zst_offset + zs->zst_stride));
+ /*
+ * XXX: use a faster division method?
+ */
+ prefetch_limit = zs->zst_offset + zs->zst_len +
+ (zs->zst_cap * zs->zst_stride) / zs->zst_len;
+
+ while (prefetch_tail < prefetch_limit) {
+ prefetch_ofst = zs->zst_offset + zs->zst_direction *
+ (prefetch_tail - zs->zst_offset);
+
+ prefetch_len = zs->zst_len;
+
+ /*
+ * Don't prefetch beyond the end of the file, if working
+ * backwards.
+ */
+ if ((zs->zst_direction == ZFETCH_BACKWARD) &&
+ (prefetch_ofst > prefetch_tail)) {
+ prefetch_len += prefetch_ofst;
+ prefetch_ofst = 0;
+ }
+
+ /* don't prefetch more than we're supposed to */
+ if (prefetch_len > zs->zst_len)
+ break;
+
+ blocks_fetched = dmu_zfetch_fetch(zf->zf_dnode,
+ prefetch_ofst, zs->zst_len);
+
+ prefetch_tail += zs->zst_stride;
+ /* stop if we've run out of stuff to prefetch */
+ if (blocks_fetched < zs->zst_len)
+ break;
+ }
+ zs->zst_ph_offset = prefetch_tail;
+ zs->zst_last = ddi_get_lbolt();
+}
+
+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;
+ zf->zf_stream_cnt = 0;
+ zf->zf_alloc_fail = 0;
+
+ list_create(&zf->zf_stream, sizeof (zstream_t),
+ offsetof(zstream_t, zst_node));
+
+ rw_init(&zf->zf_rwlock, NULL, RW_DEFAULT, NULL);
+}
+
+/*
+ * This function computes the actual size, in blocks, that can be prefetched,
+ * and fetches it.
+ */
+static uint64_t
+dmu_zfetch_fetch(dnode_t *dn, uint64_t blkid, uint64_t nblks)
+{
+ uint64_t fetchsz;
+ uint64_t i;
+
+ fetchsz = dmu_zfetch_fetchsz(dn, blkid, nblks);
+
+ for (i = 0; i < fetchsz; i++) {
+ dbuf_prefetch(dn, blkid + i);
+ }
+
+ return (fetchsz);
+}
+
+/*
+ * this function returns the number of blocks that would be prefetched, based
+ * upon the supplied dnode, blockid, and nblks. This is used so that we can
+ * update streams in place, and then prefetch with their old value after the
+ * fact. This way, we can delay the prefetch, but subsequent accesses to the
+ * stream won't result in the same data being prefetched multiple times.
+ */
+static uint64_t
+dmu_zfetch_fetchsz(dnode_t *dn, uint64_t blkid, uint64_t nblks)
+{
+ uint64_t fetchsz;
+
+ if (blkid > dn->dn_maxblkid) {
+ return (0);
+ }
+
+ /* compute fetch size */
+ if (blkid + nblks + 1 > dn->dn_maxblkid) {
+ fetchsz = (dn->dn_maxblkid - blkid) + 1;
+ ASSERT(blkid + fetchsz - 1 <= dn->dn_maxblkid);
+ } else {
+ fetchsz = nblks;
+ }
+
+
+ return (fetchsz);
+}
+
+/*
+ * given a zfetch and a zstream structure, see if there is an associated zstream
+ * for this block read. If so, it starts a prefetch for the stream it
+ * located and returns true, otherwise it returns false
+ */
+static int
+dmu_zfetch_find(zfetch_t *zf, zstream_t *zh, int prefetched)
+{
+ zstream_t *zs;
+ int64_t diff;
+ int reset = !prefetched;
+ int rc = 0;
+
+ if (zh == NULL)
+ return (0);
+
+ /*
+ * XXX: This locking strategy is a bit coarse; however, it's impact has
+ * yet to be tested. If this turns out to be an issue, it can be
+ * modified in a number of different ways.
+ */
+
+ rw_enter(&zf->zf_rwlock, RW_READER);
+top:
+
+ for (zs = list_head(&zf->zf_stream); zs;
+ zs = list_next(&zf->zf_stream, zs)) {
+
+ /*
+ * XXX - should this be an assert?
+ */
+ if (zs->zst_len == 0) {
+ /* bogus stream */
+ ZFETCHSTAT_BUMP(zfetchstat_bogus_streams);
+ continue;
+ }
+
+ /*
+ * We hit this case when we are in a strided prefetch stream:
+ * we will read "len" blocks before "striding".
+ */
+ if (zh->zst_offset >= zs->zst_offset &&
+ zh->zst_offset < zs->zst_offset + zs->zst_len) {
+ if (prefetched) {
+ /* already fetched */
+ ZFETCHSTAT_BUMP(zfetchstat_stride_hits);
+ rc = 1;
+ goto out;
+ } else {
+ ZFETCHSTAT_BUMP(zfetchstat_stride_misses);
+ }
+ }
+
+ /*
+ * This is the forward sequential read case: we increment
+ * len by one each time we hit here, so we will enter this
+ * case on every read.
+ */
+ if (zh->zst_offset == zs->zst_offset + zs->zst_len) {
+
+ reset = !prefetched && zs->zst_len > 1;
+
+ mutex_enter(&zs->zst_lock);
+
+ if (zh->zst_offset != zs->zst_offset + zs->zst_len) {
+ mutex_exit(&zs->zst_lock);
+ goto top;
+ }
+ zs->zst_len += zh->zst_len;
+ diff = zs->zst_len - zfetch_block_cap;
+ if (diff > 0) {
+ zs->zst_offset += diff;
+ zs->zst_len = zs->zst_len > diff ?
+ zs->zst_len - diff : 0;
+ }
+ zs->zst_direction = ZFETCH_FORWARD;
+
+ break;
+
+ /*
+ * Same as above, but reading backwards through the file.
+ */
+ } else if (zh->zst_offset == zs->zst_offset - zh->zst_len) {
+ /* backwards sequential access */
+
+ reset = !prefetched && zs->zst_len > 1;
+
+ mutex_enter(&zs->zst_lock);
+
+ if (zh->zst_offset != zs->zst_offset - zh->zst_len) {
+ mutex_exit(&zs->zst_lock);
+ goto top;
+ }
+
+ zs->zst_offset = zs->zst_offset > zh->zst_len ?
+ zs->zst_offset - zh->zst_len : 0;
+ zs->zst_ph_offset = zs->zst_ph_offset > zh->zst_len ?
+ zs->zst_ph_offset - zh->zst_len : 0;
+ zs->zst_len += zh->zst_len;
+
+ diff = zs->zst_len - zfetch_block_cap;
+ if (diff > 0) {
+ zs->zst_ph_offset = zs->zst_ph_offset > diff ?
+ zs->zst_ph_offset - diff : 0;
+ zs->zst_len = zs->zst_len > diff ?
+ zs->zst_len - diff : zs->zst_len;
+ }
+ zs->zst_direction = ZFETCH_BACKWARD;
+
+ break;
+
+ } else if ((zh->zst_offset - zs->zst_offset - zs->zst_stride <
+ zs->zst_len) && (zs->zst_len != zs->zst_stride)) {
+ /* strided forward access */
+
+ mutex_enter(&zs->zst_lock);
+
+ if ((zh->zst_offset - zs->zst_offset - zs->zst_stride >=
+ zs->zst_len) || (zs->zst_len == zs->zst_stride)) {
+ mutex_exit(&zs->zst_lock);
+ goto top;
+ }
+
+ zs->zst_offset += zs->zst_stride;
+ zs->zst_direction = ZFETCH_FORWARD;
+
+ break;
+
+ } else if ((zh->zst_offset - zs->zst_offset + zs->zst_stride <
+ zs->zst_len) && (zs->zst_len != zs->zst_stride)) {
+ /* strided reverse access */
+
+ mutex_enter(&zs->zst_lock);
+
+ if ((zh->zst_offset - zs->zst_offset + zs->zst_stride >=
+ zs->zst_len) || (zs->zst_len == zs->zst_stride)) {
+ mutex_exit(&zs->zst_lock);
+ goto top;
+ }
+
+ zs->zst_offset = zs->zst_offset > zs->zst_stride ?
+ zs->zst_offset - zs->zst_stride : 0;
+ zs->zst_ph_offset = (zs->zst_ph_offset >
+ (2 * zs->zst_stride)) ?
+ (zs->zst_ph_offset - (2 * zs->zst_stride)) : 0;
+ zs->zst_direction = ZFETCH_BACKWARD;
+
+ break;
+ }
+ }
+
+ if (zs) {
+ if (reset) {
+ zstream_t *remove = zs;
+
+ ZFETCHSTAT_BUMP(zfetchstat_stream_resets);
+ rc = 0;
+ mutex_exit(&zs->zst_lock);
+ rw_exit(&zf->zf_rwlock);
+ rw_enter(&zf->zf_rwlock, RW_WRITER);
+ /*
+ * Relocate the stream, in case someone removes
+ * it while we were acquiring the WRITER lock.
+ */
+ for (zs = list_head(&zf->zf_stream); zs;
+ zs = list_next(&zf->zf_stream, zs)) {
+ if (zs == remove) {
+ dmu_zfetch_stream_remove(zf, zs);
+ mutex_destroy(&zs->zst_lock);
+ kmem_free(zs, sizeof (zstream_t));
+ break;
+ }
+ }
+ } else {
+ ZFETCHSTAT_BUMP(zfetchstat_stream_noresets);
+ rc = 1;
+ dmu_zfetch_dofetch(zf, zs);
+ mutex_exit(&zs->zst_lock);
+ }
+ }
+out:
+ rw_exit(&zf->zf_rwlock);
+ return (rc);
+}
+
+/*
+ * Clean-up state associated with a zfetch structure. This frees allocated
+ * structure members, empties the zf_stream tree, and generally makes things
+ * nice. This doesn't free the zfetch_t itself, that's left to the caller.
+ */
+void
+dmu_zfetch_rele(zfetch_t *zf)
+{
+ zstream_t *zs;
+ zstream_t *zs_next;
+
+ ASSERT(!RW_LOCK_HELD(&zf->zf_rwlock));
+
+ for (zs = list_head(&zf->zf_stream); zs; zs = zs_next) {
+ zs_next = list_next(&zf->zf_stream, zs);
+
+ list_remove(&zf->zf_stream, zs);
+ mutex_destroy(&zs->zst_lock);
+ kmem_free(zs, sizeof (zstream_t));
+ }
+ list_destroy(&zf->zf_stream);
+ rw_destroy(&zf->zf_rwlock);
+
+ zf->zf_dnode = NULL;
+}
+
+/*
+ * Given a zfetch and zstream structure, insert the zstream structure into the
+ * AVL tree contained within the zfetch structure. Peform the appropriate
+ * book-keeping. It is possible that another thread has inserted a stream which
+ * matches one that we are about to insert, so we must be sure to check for this
+ * case. If one is found, return failure, and let the caller cleanup the
+ * duplicates.
+ */
+static int
+dmu_zfetch_stream_insert(zfetch_t *zf, zstream_t *zs)
+{
+ zstream_t *zs_walk;
+ zstream_t *zs_next;
+
+ ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
+
+ for (zs_walk = list_head(&zf->zf_stream); zs_walk; zs_walk = zs_next) {
+ zs_next = list_next(&zf->zf_stream, zs_walk);
+
+ if (dmu_zfetch_streams_equal(zs_walk, zs)) {
+ return (0);
+ }
+ }
+
+ list_insert_head(&zf->zf_stream, zs);
+ zf->zf_stream_cnt++;
+ return (1);
+}
+
+
+/*
+ * Walk the list of zstreams in the given zfetch, find an old one (by time), and
+ * reclaim it for use by the caller.
+ */
+static zstream_t *
+dmu_zfetch_stream_reclaim(zfetch_t *zf)
+{
+ zstream_t *zs;
+
+ if (! rw_tryenter(&zf->zf_rwlock, RW_WRITER))
+ return (0);
+
+ for (zs = list_head(&zf->zf_stream); zs;
+ zs = list_next(&zf->zf_stream, zs)) {
+
+ if (((ddi_get_lbolt() - zs->zst_last)/hz) > zfetch_min_sec_reap)
+ break;
+ }
+
+ if (zs) {
+ dmu_zfetch_stream_remove(zf, zs);
+ mutex_destroy(&zs->zst_lock);
+ bzero(zs, sizeof (zstream_t));
+ } else {
+ zf->zf_alloc_fail++;
+ }
+ rw_exit(&zf->zf_rwlock);
+
+ return (zs);
+}
+
+/*
+ * Given a zfetch and zstream structure, remove the zstream structure from its
+ * container in the zfetch structure. Perform the appropriate book-keeping.
+ */
+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);
+ zf->zf_stream_cnt--;
+}
+
+static int
+dmu_zfetch_streams_equal(zstream_t *zs1, zstream_t *zs2)
+{
+ if (zs1->zst_offset != zs2->zst_offset)
+ return (0);
+
+ if (zs1->zst_len != zs2->zst_len)
+ return (0);
+
+ if (zs1->zst_stride != zs2->zst_stride)
+ return (0);
+
+ if (zs1->zst_ph_offset != zs2->zst_ph_offset)
+ return (0);
+
+ if (zs1->zst_cap != zs2->zst_cap)
+ return (0);
+
+ if (zs1->zst_direction != zs2->zst_direction)
+ return (0);
+
+ return (1);
+}
+
+/*
+ * This is the prefetch entry point. It calls all of the other dmu_zfetch
+ * routines to create, delete, find, or operate upon prefetch streams.
+ */
+void
+dmu_zfetch(zfetch_t *zf, uint64_t offset, uint64_t size, int prefetched)
+{
+ zstream_t zst;
+ zstream_t *newstream;
+ int fetched;
+ int inserted;
+ unsigned int blkshft;
+ uint64_t blksz;
+
+ if (zfs_prefetch_disable)
+ return;
+
+ /* files that aren't ln2 blocksz are only one block -- nothing to do */
+ if (!zf->zf_dnode->dn_datablkshift)
+ return;
+
+ /* convert offset and size, into blockid and nblocks */
+ blkshft = zf->zf_dnode->dn_datablkshift;
+ blksz = (1 << blkshft);
+
+ bzero(&zst, sizeof (zstream_t));
+ zst.zst_offset = offset >> blkshft;
+ zst.zst_len = (P2ROUNDUP(offset + size, blksz) -
+ P2ALIGN(offset, blksz)) >> blkshft;
+
+ fetched = dmu_zfetch_find(zf, &zst, prefetched);
+ if (fetched) {
+ ZFETCHSTAT_BUMP(zfetchstat_hits);
+ } else {
+ ZFETCHSTAT_BUMP(zfetchstat_misses);
+ if (fetched = dmu_zfetch_colinear(zf, &zst)) {
+ ZFETCHSTAT_BUMP(zfetchstat_colinear_hits);
+ } else {
+ ZFETCHSTAT_BUMP(zfetchstat_colinear_misses);
+ }
+ }
+
+ if (!fetched) {
+ newstream = dmu_zfetch_stream_reclaim(zf);
+
+ /*
+ * we still couldn't find a stream, drop the lock, and allocate
+ * one if possible. Otherwise, give up and go home.
+ */
+ if (newstream) {
+ ZFETCHSTAT_BUMP(zfetchstat_reclaim_successes);
+ } else {
+ uint64_t maxblocks;
+ uint32_t max_streams;
+ uint32_t cur_streams;
+
+ ZFETCHSTAT_BUMP(zfetchstat_reclaim_failures);
+ cur_streams = zf->zf_stream_cnt;
+ maxblocks = zf->zf_dnode->dn_maxblkid;
+
+ max_streams = MIN(zfetch_max_streams,
+ (maxblocks / zfetch_block_cap));
+ if (max_streams == 0) {
+ max_streams++;
+ }
+
+ if (cur_streams >= max_streams) {
+ return;
+ }
+ newstream = kmem_zalloc(sizeof (zstream_t), KM_SLEEP);
+ }
+
+ newstream->zst_offset = zst.zst_offset;
+ newstream->zst_len = zst.zst_len;
+ newstream->zst_stride = zst.zst_len;
+ newstream->zst_ph_offset = zst.zst_len + zst.zst_offset;
+ newstream->zst_cap = zst.zst_len;
+ newstream->zst_direction = ZFETCH_FORWARD;
+ newstream->zst_last = ddi_get_lbolt();
+
+ mutex_init(&newstream->zst_lock, NULL, MUTEX_DEFAULT, NULL);
+
+ rw_enter(&zf->zf_rwlock, RW_WRITER);
+ inserted = dmu_zfetch_stream_insert(zf, newstream);
+ rw_exit(&zf->zf_rwlock);
+
+ if (!inserted) {
+ mutex_destroy(&newstream->zst_lock);
+ kmem_free(newstream, sizeof (zstream_t));
+ }
+ }
+}