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