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 bytes to prefetch indirects for per stream (default 64MB) */
  53 uint32_t        zfetch_max_idistance = 64 * 1024 * 1024;
  54 /* max number of bytes in an array_read in which we allow prefetching (1MB) */
  55 uint64_t        zfetch_array_rd_sz = 1024 * 1024;
  56
  57 SYSCTL_DECL(_vfs_zfs);
  58 SYSCTL_INT(_vfs_zfs, OID_AUTO, prefetch_disable, CTLFLAG_RW,
  59     &zfs_prefetch_disable, 0, "Disable prefetch");
  60 SYSCTL_NODE(_vfs_zfs, OID_AUTO, zfetch, CTLFLAG_RW, 0, "ZFS ZFETCH");
  61 SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, max_streams, CTLFLAG_RWTUN,
  62     &zfetch_max_streams, 0, "Max # of streams per zfetch");
  63 SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, min_sec_reap, CTLFLAG_RWTUN,
  64     &zfetch_min_sec_reap, 0, "Min time before stream reclaim");
  65 SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, max_distance, CTLFLAG_RWTUN,
  66     &zfetch_max_distance, 0, "Max bytes to prefetch per stream");
  67 SYSCTL_UQUAD(_vfs_zfs_zfetch, OID_AUTO, array_rd_sz, CTLFLAG_RWTUN,
  68     &zfetch_array_rd_sz, 0,
  69     "Number of bytes in a array_read at which we stop prefetching");
  70
  71 typedef struct zfetch_stats {
  72         kstat_named_t zfetchstat_hits;
  73         kstat_named_t zfetchstat_misses;
  74         kstat_named_t zfetchstat_max_streams;
  75 } zfetch_stats_t;
  76
  77 static zfetch_stats_t zfetch_stats = {
  78         { "hits",                       KSTAT_DATA_UINT64 },
  79         { "misses",                     KSTAT_DATA_UINT64 },
  80         { "max_streams",                KSTAT_DATA_UINT64 },
  81 };
  82
  83 #define ZFETCHSTAT_BUMP(stat) \
  84         atomic_inc_64(&zfetch_stats.stat.value.ui64);
  85
  86 kstat_t         *zfetch_ksp;
  87
  88 void
  89 zfetch_init(void)
  90 {
  91         zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc",
  92             KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t),
  93             KSTAT_FLAG_VIRTUAL);
  94
  95         if (zfetch_ksp != NULL) {
  96                 zfetch_ksp->ks_data = &zfetch_stats;
  97                 kstat_install(zfetch_ksp);
  98         }
  99 }
 100
 101 void
 102 zfetch_fini(void)
 103 {
 104         if (zfetch_ksp != NULL) {
 105                 kstat_delete(zfetch_ksp);
 106                 zfetch_ksp = NULL;
 107         }
 108 }
 109
 110 /*
 111  * This takes a pointer to a zfetch structure and a dnode.  It performs the
 112  * necessary setup for the zfetch structure, grokking data from the
 113  * associated dnode.
 114  */
 115 void
 116 dmu_zfetch_init(zfetch_t *zf, dnode_t *dno)
 117 {
 118         if (zf == NULL)
 119                 return;
 120
 121         zf->zf_dnode = dno;
 122
 123         list_create(&zf->zf_stream, sizeof (zstream_t),
 124             offsetof(zstream_t, zs_node));
 125
 126         rw_init(&zf->zf_rwlock, NULL, RW_DEFAULT, NULL);
 127 }
 128
 129 static void
 130 dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs)
 131 {
 132         ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
 133         list_remove(&zf->zf_stream, zs);
 134         mutex_destroy(&zs->zs_lock);
 135         kmem_free(zs, sizeof (*zs));
 136 }
 137
 138 /*
 139  * Clean-up state associated with a zfetch structure (e.g. destroy the
 140  * streams).  This doesn't free the zfetch_t itself, that's left to the caller.
 141  */
 142 void
 143 dmu_zfetch_fini(zfetch_t *zf)
 144 {
 145         zstream_t *zs;
 146
 147         ASSERT(!RW_LOCK_HELD(&zf->zf_rwlock));
 148
 149         rw_enter(&zf->zf_rwlock, RW_WRITER);
 150         while ((zs = list_head(&zf->zf_stream)) != NULL)
 151                 dmu_zfetch_stream_remove(zf, zs);
 152         rw_exit(&zf->zf_rwlock);
 153         list_destroy(&zf->zf_stream);
 154         rw_destroy(&zf->zf_rwlock);
 155
 156         zf->zf_dnode = NULL;
 157 }
 158
 159 /*
 160  * If there aren't too many streams already, create a new stream.
 161  * The "blkid" argument is the next block that we expect this stream to access.
 162  * While we're here, clean up old streams (which haven't been
 163  * accessed for at least zfetch_min_sec_reap seconds).
 164  */
 165 static void
 166 dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid)
 167 {
 168         zstream_t *zs_next;
 169         int numstreams = 0;
 170
 171         ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
 172
 173         /*
 174          * Clean up old streams.
 175          */
 176         for (zstream_t *zs = list_head(&zf->zf_stream);
 177             zs != NULL; zs = zs_next) {
 178                 zs_next = list_next(&zf->zf_stream, zs);
 179                 if (((gethrtime() - zs->zs_atime) / NANOSEC) >
 180                     zfetch_min_sec_reap)
 181                         dmu_zfetch_stream_remove(zf, zs);
 182                 else
 183                         numstreams++;
 184         }
 185
 186         /*
 187          * The maximum number of streams is normally zfetch_max_streams,
 188          * but for small files we lower it such that it's at least possible
 189          * for all the streams to be non-overlapping.
 190          *
 191          * If we are already at the maximum number of streams for this file,
 192          * even after removing old streams, then don't create this stream.
 193          */
 194         uint32_t max_streams = MAX(1, MIN(zfetch_max_streams,
 195             zf->zf_dnode->dn_maxblkid * zf->zf_dnode->dn_datablksz /
 196             zfetch_max_distance));
 197         if (numstreams >= max_streams) {
 198                 ZFETCHSTAT_BUMP(zfetchstat_max_streams);
 199                 return;
 200         }
 201
 202         zstream_t *zs = kmem_zalloc(sizeof (*zs), KM_SLEEP);
 203         zs->zs_blkid = blkid;
 204         zs->zs_pf_blkid = blkid;
 205         zs->zs_ipf_blkid = blkid;
 206         zs->zs_atime = gethrtime();
 207         mutex_init(&zs->zs_lock, NULL, MUTEX_DEFAULT, NULL);
 208
 209         list_insert_head(&zf->zf_stream, zs);
 210 }
 211
 212 /*
 213  * This is the predictive prefetch entry point.  It associates dnode access
 214  * specified with blkid and nblks arguments with prefetch stream, predicts
 215  * further accesses based on that stats and initiates speculative prefetch.
 216  * fetch_data argument specifies whether actual data blocks should be fetched:
 217  *   FALSE -- prefetch only indirect blocks for predicted data blocks;
 218  *   TRUE -- prefetch predicted data blocks plus following indirect blocks.
 219  */
 220 void
 221 dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks, boolean_t fetch_data)
 222 {
 223         zstream_t *zs;
 224         int64_t pf_start, ipf_start, ipf_istart, ipf_iend;
 225         int64_t pf_ahead_blks, max_blks;
 226         int epbs, max_dist_blks, pf_nblks, ipf_nblks;
 227         uint64_t end_of_access_blkid = blkid + nblks;
 228
 229         if (zfs_prefetch_disable)
 230                 return;
 231
 232         /*
 233          * As a fast path for small (single-block) files, ignore access
 234          * to the first block.
 235          */
 236         if (blkid == 0)
 237                 return;
 238
 239         rw_enter(&zf->zf_rwlock, RW_READER);
 240
 241         for (zs = list_head(&zf->zf_stream); zs != NULL;
 242             zs = list_next(&zf->zf_stream, zs)) {
 243                 if (blkid == zs->zs_blkid) {
 244                         mutex_enter(&zs->zs_lock);
 245                         /*
 246                          * zs_blkid could have changed before we
 247                          * acquired zs_lock; re-check them here.
 248                          */
 249                         if (blkid != zs->zs_blkid) {
 250                                 mutex_exit(&zs->zs_lock);
 251                                 continue;
 252                         }
 253                         break;
 254                 }
 255         }
 256
 257         if (zs == NULL) {
 258                 /*
 259                  * This access is not part of any existing stream.  Create
 260                  * a new stream for it.
 261                  */
 262                 ZFETCHSTAT_BUMP(zfetchstat_misses);
 263                 if (rw_tryupgrade(&zf->zf_rwlock))
 264                         dmu_zfetch_stream_create(zf, end_of_access_blkid);
 265                 rw_exit(&zf->zf_rwlock);
 266                 return;
 267         }
 268
 269         /*
 270          * This access was to a block that we issued a prefetch for on
 271          * behalf of this stream. Issue further prefetches for this stream.
 272          *
 273          * Normally, we start prefetching where we stopped
 274          * prefetching last (zs_pf_blkid).  But when we get our first
 275          * hit on this stream, zs_pf_blkid == zs_blkid, we don't
 276          * want to prefetch the block we just accessed.  In this case,
 277          * start just after the block we just accessed.
 278          */
 279         pf_start = MAX(zs->zs_pf_blkid, end_of_access_blkid);
 280
 281         /*
 282          * Double our amount of prefetched data, but don't let the
 283          * prefetch get further ahead than zfetch_max_distance.
 284          */
 285         if (fetch_data) {
 286                 max_dist_blks =
 287                     zfetch_max_distance >> zf->zf_dnode->dn_datablkshift;
 288                 /*
 289                  * Previously, we were (zs_pf_blkid - blkid) ahead.  We
 290                  * want to now be double that, so read that amount again,
 291                  * plus the amount we are catching up by (i.e. the amount
 292                  * read just now).
 293                  */
 294                 pf_ahead_blks = zs->zs_pf_blkid - blkid + nblks;
 295                 max_blks = max_dist_blks - (pf_start - end_of_access_blkid);
 296                 pf_nblks = MIN(pf_ahead_blks, max_blks);
 297         } else {
 298                 pf_nblks = 0;
 299         }
 300
 301         zs->zs_pf_blkid = pf_start + pf_nblks;
 302
 303         /*
 304          * Do the same for indirects, starting from where we stopped last,
 305          * or where we will stop reading data blocks (and the indirects
 306          * that point to them).
 307          */
 308         ipf_start = MAX(zs->zs_ipf_blkid, zs->zs_pf_blkid);
 309         max_dist_blks = zfetch_max_idistance >> zf->zf_dnode->dn_datablkshift;
 310         /*
 311          * We want to double our distance ahead of the data prefetch
 312          * (or reader, if we are not prefetching data).  Previously, we
 313          * were (zs_ipf_blkid - blkid) ahead.  To double that, we read
 314          * that amount again, plus the amount we are catching up by
 315          * (i.e. the amount read now + the amount of data prefetched now).
 316          */
 317         pf_ahead_blks = zs->zs_ipf_blkid - blkid + nblks + pf_nblks;
 318         max_blks = max_dist_blks - (ipf_start - end_of_access_blkid);
 319         ipf_nblks = MIN(pf_ahead_blks, max_blks);
 320         zs->zs_ipf_blkid = ipf_start + ipf_nblks;
 321
 322         epbs = zf->zf_dnode->dn_indblkshift - SPA_BLKPTRSHIFT;
 323         ipf_istart = P2ROUNDUP(ipf_start, 1 << epbs) >> epbs;
 324         ipf_iend = P2ROUNDUP(zs->zs_ipf_blkid, 1 << epbs) >> epbs;
 325
 326         zs->zs_atime = gethrtime();
 327         zs->zs_blkid = end_of_access_blkid;
 328         mutex_exit(&zs->zs_lock);
 329         rw_exit(&zf->zf_rwlock);
 330
 331         /*
 332          * dbuf_prefetch() is asynchronous (even when it needs to read
 333          * indirect blocks), but we still prefer to drop our locks before
 334          * calling it to reduce the time we hold them.
 335          */
 336
 337         for (int i = 0; i < pf_nblks; i++) {
 338                 dbuf_prefetch(zf->zf_dnode, 0, pf_start + i,
 339                     ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH);
 340         }
 341         for (int64_t iblk = ipf_istart; iblk < ipf_iend; iblk++) {
 342                 dbuf_prefetch(zf->zf_dnode, 1, iblk,
 343                     ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH);
 344         }
 345         ZFETCHSTAT_BUMP(zfetchstat_hits);
 346 }