sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_zfetch.c

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 /*
  22  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  23  * Use is subject to license terms.
  24  */
  25
  26 /*
  27  * Copyright (c) 2013, 2015 by Delphix. All rights reserved.
  28  */
  29
  30 #include <sys/zfs_context.h>
  31 #include <sys/dnode.h>
  32 #include <sys/dmu_objset.h>
  33 #include <sys/dmu_zfetch.h>
  34 #include <sys/dmu.h>
  35 #include <sys/dbuf.h>
  36 #include <sys/kstat.h>
  37
  38 /*
  39  * This tunable disables predictive prefetch.  Note that it leaves "prescient"
  40  * prefetch (e.g. prefetch for zfs send) intact.  Unlike predictive prefetch,
  41  * prescient prefetch never issues i/os that end up not being needed,
  42  * so it can't hurt performance.
  43  */
  44 boolean_t zfs_prefetch_disable = B_FALSE;
  45
  46 /* max # of streams per zfetch */
  47 uint32_t        zfetch_max_streams = 8;
  48 /* min time before stream reclaim */
  49 uint32_t        zfetch_min_sec_reap = 2;
  50 /* max bytes to prefetch per stream (default 8MB) */
  51 uint32_t        zfetch_max_distance = 8 * 1024 * 1024;
  52 /* max number of bytes in an array_read in which we allow prefetching (1MB) */
  53 uint64_t        zfetch_array_rd_sz = 1024 * 1024;
  54
  55 SYSCTL_DECL(_vfs_zfs);
  56 SYSCTL_INT(_vfs_zfs, OID_AUTO, prefetch_disable, CTLFLAG_RW,
  57     &zfs_prefetch_disable, 0, "Disable prefetch");
  58 SYSCTL_NODE(_vfs_zfs, OID_AUTO, zfetch, CTLFLAG_RW, 0, "ZFS ZFETCH");
  59 SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, max_streams, CTLFLAG_RWTUN,
  60     &zfetch_max_streams, 0, "Max # of streams per zfetch");
  61 SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, min_sec_reap, CTLFLAG_RWTUN,
  62     &zfetch_min_sec_reap, 0, "Min time before stream reclaim");
  63 SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, max_distance, CTLFLAG_RWTUN,
  64     &zfetch_max_distance, 0, "Max bytes to prefetch per stream");
  65 SYSCTL_UQUAD(_vfs_zfs_zfetch, OID_AUTO, array_rd_sz, CTLFLAG_RWTUN,
  66     &zfetch_array_rd_sz, 0,
  67     "Number of bytes in a array_read at which we stop prefetching");
  68
  69 typedef struct zfetch_stats {
  70         kstat_named_t zfetchstat_hits;
  71         kstat_named_t zfetchstat_misses;
  72         kstat_named_t zfetchstat_max_streams;
  73 } zfetch_stats_t;
  74
  75 static zfetch_stats_t zfetch_stats = {
  76         { "hits",                       KSTAT_DATA_UINT64 },
  77         { "misses",                     KSTAT_DATA_UINT64 },
  78         { "max_streams",                KSTAT_DATA_UINT64 },
  79 };
  80
  81 #define ZFETCHSTAT_BUMP(stat) \
  82         atomic_inc_64(&zfetch_stats.stat.value.ui64);
  83
  84 kstat_t         *zfetch_ksp;
  85
  86 void
  87 zfetch_init(void)
  88 {
  89         zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc",
  90             KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t),
  91             KSTAT_FLAG_VIRTUAL);
  92
  93         if (zfetch_ksp != NULL) {
  94                 zfetch_ksp->ks_data = &zfetch_stats;
  95                 kstat_install(zfetch_ksp);
  96         }
  97 }
  98
  99 void
 100 zfetch_fini(void)
 101 {
 102         if (zfetch_ksp != NULL) {
 103                 kstat_delete(zfetch_ksp);
 104                 zfetch_ksp = NULL;
 105         }
 106 }
 107
 108 /*
 109  * This takes a pointer to a zfetch structure and a dnode.  It performs the
 110  * necessary setup for the zfetch structure, grokking data from the
 111  * associated dnode.
 112  */
 113 void
 114 dmu_zfetch_init(zfetch_t *zf, dnode_t *dno)
 115 {
 116         if (zf == NULL)
 117                 return;
 118
 119         zf->zf_dnode = dno;
 120
 121         list_create(&zf->zf_stream, sizeof (zstream_t),
 122             offsetof(zstream_t, zs_node));
 123
 124         rw_init(&zf->zf_rwlock, NULL, RW_DEFAULT, NULL);
 125 }
 126
 127 static void
 128 dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs)
 129 {
 130         ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
 131         list_remove(&zf->zf_stream, zs);
 132         mutex_destroy(&zs->zs_lock);
 133         kmem_free(zs, sizeof (*zs));
 134 }
 135
 136 /*
 137  * Clean-up state associated with a zfetch structure (e.g. destroy the
 138  * streams).  This doesn't free the zfetch_t itself, that's left to the caller.
 139  */
 140 void
 141 dmu_zfetch_fini(zfetch_t *zf)
 142 {
 143         zstream_t *zs;
 144
 145         ASSERT(!RW_LOCK_HELD(&zf->zf_rwlock));
 146
 147         rw_enter(&zf->zf_rwlock, RW_WRITER);
 148         while ((zs = list_head(&zf->zf_stream)) != NULL)
 149                 dmu_zfetch_stream_remove(zf, zs);
 150         rw_exit(&zf->zf_rwlock);
 151         list_destroy(&zf->zf_stream);
 152         rw_destroy(&zf->zf_rwlock);
 153
 154         zf->zf_dnode = NULL;
 155 }
 156
 157 /*
 158  * If there aren't too many streams already, create a new stream.
 159  * The "blkid" argument is the next block that we expect this stream to access.
 160  * While we're here, clean up old streams (which haven't been
 161  * accessed for at least zfetch_min_sec_reap seconds).
 162  */
 163 static void
 164 dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid)
 165 {
 166         zstream_t *zs_next;
 167         int numstreams = 0;
 168
 169         ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
 170
 171         /*
 172          * Clean up old streams.
 173          */
 174         for (zstream_t *zs = list_head(&zf->zf_stream);
 175             zs != NULL; zs = zs_next) {
 176                 zs_next = list_next(&zf->zf_stream, zs);
 177                 if (((gethrtime() - zs->zs_atime) / NANOSEC) >
 178                     zfetch_min_sec_reap)
 179                         dmu_zfetch_stream_remove(zf, zs);
 180                 else
 181                         numstreams++;
 182         }
 183
 184         /*
 185          * The maximum number of streams is normally zfetch_max_streams,
 186          * but for small files we lower it such that it's at least possible
 187          * for all the streams to be non-overlapping.
 188          *
 189          * If we are already at the maximum number of streams for this file,
 190          * even after removing old streams, then don't create this stream.
 191          */
 192         uint32_t max_streams = MAX(1, MIN(zfetch_max_streams,
 193             zf->zf_dnode->dn_maxblkid * zf->zf_dnode->dn_datablksz /
 194             zfetch_max_distance));
 195         if (numstreams >= max_streams) {
 196                 ZFETCHSTAT_BUMP(zfetchstat_max_streams);
 197                 return;
 198         }
 199
 200         zstream_t *zs = kmem_zalloc(sizeof (*zs), KM_SLEEP);
 201         zs->zs_blkid = blkid;
 202         zs->zs_pf_blkid = blkid;
 203         zs->zs_atime = gethrtime();
 204         mutex_init(&zs->zs_lock, NULL, MUTEX_DEFAULT, NULL);
 205
 206         list_insert_head(&zf->zf_stream, zs);
 207 }
 208
 209 /*
 210  * This is the prefetch entry point.  It calls all of the other dmu_zfetch
 211  * routines to create, delete, find, or operate upon prefetch streams.
 212  */
 213 void
 214 dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks)
 215 {
 216         zstream_t *zs;
 217
 218         if (zfs_prefetch_disable)
 219                 return;
 220
 221         /*
 222          * As a fast path for small (single-block) files, ignore access
 223          * to the first block.
 224          */
 225         if (blkid == 0)
 226                 return;
 227
 228         rw_enter(&zf->zf_rwlock, RW_READER);
 229
 230         for (zs = list_head(&zf->zf_stream); zs != NULL;
 231             zs = list_next(&zf->zf_stream, zs)) {
 232                 if (blkid == zs->zs_blkid) {
 233                         mutex_enter(&zs->zs_lock);
 234                         /*
 235                          * zs_blkid could have changed before we
 236                          * acquired zs_lock; re-check them here.
 237                          */
 238                         if (blkid != zs->zs_blkid) {
 239                                 mutex_exit(&zs->zs_lock);
 240                                 continue;
 241                         }
 242                         break;
 243                 }
 244         }
 245
 246         if (zs == NULL) {
 247                 /*
 248                  * This access is not part of any existing stream.  Create
 249                  * a new stream for it.
 250                  */
 251                 ZFETCHSTAT_BUMP(zfetchstat_misses);
 252                 if (rw_tryupgrade(&zf->zf_rwlock))
 253                         dmu_zfetch_stream_create(zf, blkid + nblks);
 254                 rw_exit(&zf->zf_rwlock);
 255                 return;
 256         }
 257
 258         /*
 259          * This access was to a block that we issued a prefetch for on
 260          * behalf of this stream. Issue further prefetches for this stream.
 261          *
 262          * Normally, we start prefetching where we stopped
 263          * prefetching last (zs_pf_blkid).  But when we get our first
 264          * hit on this stream, zs_pf_blkid == zs_blkid, we don't
 265          * want to prefetch to block we just accessed.  In this case,
 266          * start just after the block we just accessed.
 267          */
 268         int64_t pf_start = MAX(zs->zs_pf_blkid, blkid + nblks);
 269
 270         /*
 271          * Double our amount of prefetched data, but don't let the
 272          * prefetch get further ahead than zfetch_max_distance.
 273          */
 274         int pf_nblks =
 275             MIN((int64_t)zs->zs_pf_blkid - zs->zs_blkid + nblks,
 276             zs->zs_blkid + nblks +
 277             (zfetch_max_distance >> zf->zf_dnode->dn_datablkshift) - pf_start);
 278
 279         zs->zs_pf_blkid = pf_start + pf_nblks;
 280         zs->zs_atime = gethrtime();
 281         zs->zs_blkid = blkid + nblks;
 282
 283         /*
 284          * dbuf_prefetch() issues the prefetch i/o
 285          * asynchronously, but it may need to wait for an
 286          * indirect block to be read from disk.  Therefore
 287          * we do not want to hold any locks while we call it.
 288          */
 289         mutex_exit(&zs->zs_lock);
 290         rw_exit(&zf->zf_rwlock);
 291         for (int i = 0; i < pf_nblks; i++) {
 292                 dbuf_prefetch(zf->zf_dnode, 0, pf_start + i,
 293                     ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH);
 294         }
 295         ZFETCHSTAT_BUMP(zfetchstat_hits);
 296 }