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 | CTLFLAG_MPSAFE, 0,
  61     "ZFS ZFETCH");
  62 SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, max_streams, CTLFLAG_RWTUN,
  63     &zfetch_max_streams, 0, "Max # of streams per zfetch");
  64 SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, min_sec_reap, CTLFLAG_RWTUN,
  65     &zfetch_min_sec_reap, 0, "Min time before stream reclaim");
  66 SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, max_distance, CTLFLAG_RWTUN,
  67     &zfetch_max_distance, 0, "Max bytes to prefetch per stream");
  68 SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, max_idistance, CTLFLAG_RWTUN,
  69     &zfetch_max_idistance, 0, "Max bytes to prefetch indirects for per stream");
  70 SYSCTL_UQUAD(_vfs_zfs_zfetch, OID_AUTO, array_rd_sz, CTLFLAG_RWTUN,
  71     &zfetch_array_rd_sz, 0,
  72     "Number of bytes in a array_read at which we stop prefetching");
  73
  74 typedef struct zfetch_stats {
  75         kstat_named_t zfetchstat_hits;
  76         kstat_named_t zfetchstat_misses;
  77         kstat_named_t zfetchstat_max_streams;
  78 } zfetch_stats_t;
  79
  80 static zfetch_stats_t zfetch_stats = {
  81         { "hits",                       KSTAT_DATA_UINT64 },
  82         { "misses",                     KSTAT_DATA_UINT64 },
  83         { "max_streams",                KSTAT_DATA_UINT64 },
  84 };
  85
  86 #define ZFETCHSTAT_BUMP(stat) \
  87         atomic_inc_64(&zfetch_stats.stat.value.ui64);
  88
  89 kstat_t         *zfetch_ksp;
  90
  91 void
  92 zfetch_init(void)
  93 {
  94         zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc",
  95             KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t),
  96             KSTAT_FLAG_VIRTUAL);
  97
  98         if (zfetch_ksp != NULL) {
  99                 zfetch_ksp->ks_data = &zfetch_stats;
 100                 kstat_install(zfetch_ksp);
 101         }
 102 }
 103
 104 void
 105 zfetch_fini(void)
 106 {
 107         if (zfetch_ksp != NULL) {
 108                 kstat_delete(zfetch_ksp);
 109                 zfetch_ksp = NULL;
 110         }
 111 }
 112
 113 /*
 114  * This takes a pointer to a zfetch structure and a dnode.  It performs the
 115  * necessary setup for the zfetch structure, grokking data from the
 116  * associated dnode.
 117  */
 118 void
 119 dmu_zfetch_init(zfetch_t *zf, dnode_t *dno)
 120 {
 121         if (zf == NULL)
 122                 return;
 123
 124         zf->zf_dnode = dno;
 125
 126         list_create(&zf->zf_stream, sizeof (zstream_t),
 127             offsetof(zstream_t, zs_node));
 128
 129         rw_init(&zf->zf_rwlock, NULL, RW_DEFAULT, NULL);
 130 }
 131
 132 static void
 133 dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs)
 134 {
 135         ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
 136         list_remove(&zf->zf_stream, zs);
 137         mutex_destroy(&zs->zs_lock);
 138         kmem_free(zs, sizeof (*zs));
 139 }
 140
 141 /*
 142  * Clean-up state associated with a zfetch structure (e.g. destroy the
 143  * streams).  This doesn't free the zfetch_t itself, that's left to the caller.
 144  */
 145 void
 146 dmu_zfetch_fini(zfetch_t *zf)
 147 {
 148         zstream_t *zs;
 149
 150         ASSERT(!RW_LOCK_HELD(&zf->zf_rwlock));
 151
 152         rw_enter(&zf->zf_rwlock, RW_WRITER);
 153         while ((zs = list_head(&zf->zf_stream)) != NULL)
 154                 dmu_zfetch_stream_remove(zf, zs);
 155         rw_exit(&zf->zf_rwlock);
 156         list_destroy(&zf->zf_stream);
 157         rw_destroy(&zf->zf_rwlock);
 158
 159         zf->zf_dnode = NULL;
 160 }
 161
 162 /*
 163  * If there aren't too many streams already, create a new stream.
 164  * The "blkid" argument is the next block that we expect this stream to access.
 165  * While we're here, clean up old streams (which haven't been
 166  * accessed for at least zfetch_min_sec_reap seconds).
 167  */
 168 static void
 169 dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid)
 170 {
 171         zstream_t *zs_next;
 172         int numstreams = 0;
 173
 174         ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
 175
 176         /*
 177          * Clean up old streams.
 178          */
 179         for (zstream_t *zs = list_head(&zf->zf_stream);
 180             zs != NULL; zs = zs_next) {
 181                 zs_next = list_next(&zf->zf_stream, zs);
 182                 if (((gethrtime() - zs->zs_atime) / NANOSEC) >
 183                     zfetch_min_sec_reap)
 184                         dmu_zfetch_stream_remove(zf, zs);
 185                 else
 186                         numstreams++;
 187         }
 188
 189         /*
 190          * The maximum number of streams is normally zfetch_max_streams,
 191          * but for small files we lower it such that it's at least possible
 192          * for all the streams to be non-overlapping.
 193          *
 194          * If we are already at the maximum number of streams for this file,
 195          * even after removing old streams, then don't create this stream.
 196          */
 197         uint32_t max_streams = MAX(1, MIN(zfetch_max_streams,
 198             zf->zf_dnode->dn_maxblkid * zf->zf_dnode->dn_datablksz /
 199             zfetch_max_distance));
 200         if (numstreams >= max_streams) {
 201                 ZFETCHSTAT_BUMP(zfetchstat_max_streams);
 202                 return;
 203         }
 204
 205         zstream_t *zs = kmem_zalloc(sizeof (*zs), KM_SLEEP);
 206         zs->zs_blkid = blkid;
 207         zs->zs_pf_blkid = blkid;
 208         zs->zs_ipf_blkid = blkid;
 209         zs->zs_atime = gethrtime();
 210         mutex_init(&zs->zs_lock, NULL, MUTEX_DEFAULT, NULL);
 211
 212         list_insert_head(&zf->zf_stream, zs);
 213 }
 214
 215 /*
 216  * This is the predictive prefetch entry point.  It associates dnode access
 217  * specified with blkid and nblks arguments with prefetch stream, predicts
 218  * further accesses based on that stats and initiates speculative prefetch.
 219  * fetch_data argument specifies whether actual data blocks should be fetched:
 220  *   FALSE -- prefetch only indirect blocks for predicted data blocks;
 221  *   TRUE -- prefetch predicted data blocks plus following indirect blocks.
 222  */
 223 void
 224 dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks, boolean_t fetch_data)
 225 {
 226         zstream_t *zs;
 227         int64_t pf_start, ipf_start, ipf_istart, ipf_iend;
 228         int64_t pf_ahead_blks, max_blks;
 229         int epbs, max_dist_blks, pf_nblks, ipf_nblks;
 230         uint64_t end_of_access_blkid = blkid + nblks;
 231         spa_t *spa = zf->zf_dnode->dn_objset->os_spa;
 232
 233         if (zfs_prefetch_disable)
 234                 return;
 235
 236         /*
 237          * If we haven't yet loaded the indirect vdevs' mappings, we
 238          * can only read from blocks that we carefully ensure are on
 239          * concrete vdevs (or previously-loaded indirect vdevs).  So we
 240          * can't allow the predictive prefetcher to attempt reads of other
 241          * blocks (e.g. of the MOS's dnode obejct).
 242          */
 243         if (!spa_indirect_vdevs_loaded(spa))
 244                 return;
 245
 246         /*
 247          * As a fast path for small (single-block) files, ignore access
 248          * to the first block.
 249          */
 250         if (blkid == 0)
 251                 return;
 252
 253         rw_enter(&zf->zf_rwlock, RW_READER);
 254
 255         /*
 256          * Find matching prefetch stream.  Depending on whether the accesses
 257          * are block-aligned, first block of the new access may either follow
 258          * the last block of the previous access, or be equal to it.
 259          */
 260         for (zs = list_head(&zf->zf_stream); zs != NULL;
 261             zs = list_next(&zf->zf_stream, zs)) {
 262                 if (blkid == zs->zs_blkid || blkid + 1 == zs->zs_blkid) {
 263                         mutex_enter(&zs->zs_lock);
 264                         /*
 265                          * zs_blkid could have changed before we
 266                          * acquired zs_lock; re-check them here.
 267                          */
 268                         if (blkid == zs->zs_blkid) {
 269                                 break;
 270                         } else if (blkid + 1 == zs->zs_blkid) {
 271                                 blkid++;
 272                                 nblks--;
 273                                 if (nblks == 0) {
 274                                         /* Already prefetched this before. */
 275                                         mutex_exit(&zs->zs_lock);
 276                                         rw_exit(&zf->zf_rwlock);
 277                                         return;
 278                                 }
 279                                 break;
 280                         }
 281                         mutex_exit(&zs->zs_lock);
 282                 }
 283         }
 284
 285         if (zs == NULL) {
 286                 /*
 287                  * This access is not part of any existing stream.  Create
 288                  * a new stream for it.
 289                  */
 290                 ZFETCHSTAT_BUMP(zfetchstat_misses);
 291                 if (rw_tryupgrade(&zf->zf_rwlock))
 292                         dmu_zfetch_stream_create(zf, end_of_access_blkid);
 293                 rw_exit(&zf->zf_rwlock);
 294                 return;
 295         }
 296
 297         /*
 298          * This access was to a block that we issued a prefetch for on
 299          * behalf of this stream. Issue further prefetches for this stream.
 300          *
 301          * Normally, we start prefetching where we stopped
 302          * prefetching last (zs_pf_blkid).  But when we get our first
 303          * hit on this stream, zs_pf_blkid == zs_blkid, we don't
 304          * want to prefetch the block we just accessed.  In this case,
 305          * start just after the block we just accessed.
 306          */
 307         pf_start = MAX(zs->zs_pf_blkid, end_of_access_blkid);
 308
 309         /*
 310          * Double our amount of prefetched data, but don't let the
 311          * prefetch get further ahead than zfetch_max_distance.
 312          */
 313         if (fetch_data) {
 314                 max_dist_blks =
 315                     zfetch_max_distance >> zf->zf_dnode->dn_datablkshift;
 316                 /*
 317                  * Previously, we were (zs_pf_blkid - blkid) ahead.  We
 318                  * want to now be double that, so read that amount again,
 319                  * plus the amount we are catching up by (i.e. the amount
 320                  * read just now).
 321                  */
 322                 pf_ahead_blks = zs->zs_pf_blkid - blkid + nblks;
 323                 max_blks = max_dist_blks - (pf_start - end_of_access_blkid);
 324                 pf_nblks = MIN(pf_ahead_blks, max_blks);
 325         } else {
 326                 pf_nblks = 0;
 327         }
 328
 329         zs->zs_pf_blkid = pf_start + pf_nblks;
 330
 331         /*
 332          * Do the same for indirects, starting from where we stopped last,
 333          * or where we will stop reading data blocks (and the indirects
 334          * that point to them).
 335          */
 336         ipf_start = MAX(zs->zs_ipf_blkid, zs->zs_pf_blkid);
 337         max_dist_blks = zfetch_max_idistance >> zf->zf_dnode->dn_datablkshift;
 338         /*
 339          * We want to double our distance ahead of the data prefetch
 340          * (or reader, if we are not prefetching data).  Previously, we
 341          * were (zs_ipf_blkid - blkid) ahead.  To double that, we read
 342          * that amount again, plus the amount we are catching up by
 343          * (i.e. the amount read now + the amount of data prefetched now).
 344          */
 345         pf_ahead_blks = zs->zs_ipf_blkid - blkid + nblks + pf_nblks;
 346         max_blks = max_dist_blks - (ipf_start - end_of_access_blkid);
 347         ipf_nblks = MIN(pf_ahead_blks, max_blks);
 348         zs->zs_ipf_blkid = ipf_start + ipf_nblks;
 349
 350         epbs = zf->zf_dnode->dn_indblkshift - SPA_BLKPTRSHIFT;
 351         ipf_istart = P2ROUNDUP(ipf_start, 1 << epbs) >> epbs;
 352         ipf_iend = P2ROUNDUP(zs->zs_ipf_blkid, 1 << epbs) >> epbs;
 353
 354         zs->zs_atime = gethrtime();
 355         zs->zs_blkid = end_of_access_blkid;
 356         mutex_exit(&zs->zs_lock);
 357         rw_exit(&zf->zf_rwlock);
 358
 359         /*
 360          * dbuf_prefetch() is asynchronous (even when it needs to read
 361          * indirect blocks), but we still prefer to drop our locks before
 362          * calling it to reduce the time we hold them.
 363          */
 364
 365         for (int i = 0; i < pf_nblks; i++) {
 366                 dbuf_prefetch(zf->zf_dnode, 0, pf_start + i,
 367                     ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH);
 368         }
 369         for (int64_t iblk = ipf_istart; iblk < ipf_iend; iblk++) {
 370                 dbuf_prefetch(zf->zf_dnode, 1, iblk,
 371                     ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH);
 372         }
 373         ZFETCHSTAT_BUMP(zfetchstat_hits);
 374 }