sys/contrib/openzfs/module/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, 2017 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 #include <sys/wmsum.h>
  38
  39 /*
  40  * This tunable disables predictive prefetch.  Note that it leaves "prescient"
  41  * prefetch (e.g. prefetch for zfs send) intact.  Unlike predictive prefetch,
  42  * prescient prefetch never issues i/os that end up not being needed,
  43  * so it can't hurt performance.
  44  */
  45
  46 static int zfs_prefetch_disable = B_FALSE;
  47
  48 /* max # of streams per zfetch */
  49 static unsigned int     zfetch_max_streams = 8;
  50 /* min time before stream reclaim */
  51 static unsigned int     zfetch_min_sec_reap = 2;
  52 /* max bytes to prefetch per stream (default 8MB) */
  53 unsigned int    zfetch_max_distance = 8 * 1024 * 1024;
  54 /* max bytes to prefetch indirects for per stream (default 64MB) */
  55 unsigned int    zfetch_max_idistance = 64 * 1024 * 1024;
  56 /* max number of bytes in an array_read in which we allow prefetching (1MB) */
  57 unsigned long   zfetch_array_rd_sz = 1024 * 1024;
  58
  59 typedef struct zfetch_stats {
  60         kstat_named_t zfetchstat_hits;
  61         kstat_named_t zfetchstat_misses;
  62         kstat_named_t zfetchstat_max_streams;
  63         kstat_named_t zfetchstat_io_issued;
  64 } zfetch_stats_t;
  65
  66 static zfetch_stats_t zfetch_stats = {
  67         { "hits",                       KSTAT_DATA_UINT64 },
  68         { "misses",                     KSTAT_DATA_UINT64 },
  69         { "max_streams",                KSTAT_DATA_UINT64 },
  70         { "io_issued",          KSTAT_DATA_UINT64 },
  71 };
  72
  73 struct {
  74         wmsum_t zfetchstat_hits;
  75         wmsum_t zfetchstat_misses;
  76         wmsum_t zfetchstat_max_streams;
  77         wmsum_t zfetchstat_io_issued;
  78 } zfetch_sums;
  79
  80 #define ZFETCHSTAT_BUMP(stat)                                   \
  81         wmsum_add(&zfetch_sums.stat, 1)
  82 #define ZFETCHSTAT_ADD(stat, val)                               \
  83         wmsum_add(&zfetch_sums.stat, val)
  84
  85
  86 static kstat_t          *zfetch_ksp;
  87
  88 static int
  89 zfetch_kstats_update(kstat_t *ksp, int rw)
  90 {
  91         zfetch_stats_t *zs = ksp->ks_data;
  92
  93         if (rw == KSTAT_WRITE)
  94                 return (EACCES);
  95         zs->zfetchstat_hits.value.ui64 =
  96             wmsum_value(&zfetch_sums.zfetchstat_hits);
  97         zs->zfetchstat_misses.value.ui64 =
  98             wmsum_value(&zfetch_sums.zfetchstat_misses);
  99         zs->zfetchstat_max_streams.value.ui64 =
 100             wmsum_value(&zfetch_sums.zfetchstat_max_streams);
 101         zs->zfetchstat_io_issued.value.ui64 =
 102             wmsum_value(&zfetch_sums.zfetchstat_io_issued);
 103         return (0);
 104 }
 105
 106 void
 107 zfetch_init(void)
 108 {
 109         wmsum_init(&zfetch_sums.zfetchstat_hits, 0);
 110         wmsum_init(&zfetch_sums.zfetchstat_misses, 0);
 111         wmsum_init(&zfetch_sums.zfetchstat_max_streams, 0);
 112         wmsum_init(&zfetch_sums.zfetchstat_io_issued, 0);
 113
 114         zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc",
 115             KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t),
 116             KSTAT_FLAG_VIRTUAL);
 117
 118         if (zfetch_ksp != NULL) {
 119                 zfetch_ksp->ks_data = &zfetch_stats;
 120                 zfetch_ksp->ks_update = zfetch_kstats_update;
 121                 kstat_install(zfetch_ksp);
 122         }
 123 }
 124
 125 void
 126 zfetch_fini(void)
 127 {
 128         if (zfetch_ksp != NULL) {
 129                 kstat_delete(zfetch_ksp);
 130                 zfetch_ksp = NULL;
 131         }
 132
 133         wmsum_fini(&zfetch_sums.zfetchstat_hits);
 134         wmsum_fini(&zfetch_sums.zfetchstat_misses);
 135         wmsum_fini(&zfetch_sums.zfetchstat_max_streams);
 136         wmsum_fini(&zfetch_sums.zfetchstat_io_issued);
 137 }
 138
 139 /*
 140  * This takes a pointer to a zfetch structure and a dnode.  It performs the
 141  * necessary setup for the zfetch structure, grokking data from the
 142  * associated dnode.
 143  */
 144 void
 145 dmu_zfetch_init(zfetch_t *zf, dnode_t *dno)
 146 {
 147         if (zf == NULL)
 148                 return;
 149         zf->zf_dnode = dno;
 150         zf->zf_numstreams = 0;
 151
 152         list_create(&zf->zf_stream, sizeof (zstream_t),
 153             offsetof(zstream_t, zs_node));
 154
 155         mutex_init(&zf->zf_lock, NULL, MUTEX_DEFAULT, NULL);
 156 }
 157
 158 static void
 159 dmu_zfetch_stream_fini(zstream_t *zs)
 160 {
 161         ASSERT(!list_link_active(&zs->zs_node));
 162         zfs_refcount_destroy(&zs->zs_callers);
 163         zfs_refcount_destroy(&zs->zs_refs);
 164         kmem_free(zs, sizeof (*zs));
 165 }
 166
 167 static void
 168 dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs)
 169 {
 170         ASSERT(MUTEX_HELD(&zf->zf_lock));
 171         list_remove(&zf->zf_stream, zs);
 172         zf->zf_numstreams--;
 173         membar_producer();
 174         if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0)
 175                 dmu_zfetch_stream_fini(zs);
 176 }
 177
 178 /*
 179  * Clean-up state associated with a zfetch structure (e.g. destroy the
 180  * streams).  This doesn't free the zfetch_t itself, that's left to the caller.
 181  */
 182 void
 183 dmu_zfetch_fini(zfetch_t *zf)
 184 {
 185         zstream_t *zs;
 186
 187         mutex_enter(&zf->zf_lock);
 188         while ((zs = list_head(&zf->zf_stream)) != NULL)
 189                 dmu_zfetch_stream_remove(zf, zs);
 190         mutex_exit(&zf->zf_lock);
 191         list_destroy(&zf->zf_stream);
 192         mutex_destroy(&zf->zf_lock);
 193
 194         zf->zf_dnode = NULL;
 195 }
 196
 197 /*
 198  * If there aren't too many streams already, create a new stream.
 199  * The "blkid" argument is the next block that we expect this stream to access.
 200  * While we're here, clean up old streams (which haven't been
 201  * accessed for at least zfetch_min_sec_reap seconds).
 202  */
 203 static void
 204 dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid)
 205 {
 206         zstream_t *zs_next;
 207         hrtime_t now = gethrtime();
 208
 209         ASSERT(MUTEX_HELD(&zf->zf_lock));
 210
 211         /*
 212          * Clean up old streams.
 213          */
 214         for (zstream_t *zs = list_head(&zf->zf_stream);
 215             zs != NULL; zs = zs_next) {
 216                 zs_next = list_next(&zf->zf_stream, zs);
 217                 /*
 218                  * Skip if still active.  1 -- zf_stream reference.
 219                  */
 220                 if (zfs_refcount_count(&zs->zs_refs) != 1)
 221                         continue;
 222                 if (((now - zs->zs_atime) / NANOSEC) >
 223                     zfetch_min_sec_reap)
 224                         dmu_zfetch_stream_remove(zf, zs);
 225         }
 226
 227         /*
 228          * The maximum number of streams is normally zfetch_max_streams,
 229          * but for small files we lower it such that it's at least possible
 230          * for all the streams to be non-overlapping.
 231          *
 232          * If we are already at the maximum number of streams for this file,
 233          * even after removing old streams, then don't create this stream.
 234          */
 235         uint32_t max_streams = MAX(1, MIN(zfetch_max_streams,
 236             zf->zf_dnode->dn_maxblkid * zf->zf_dnode->dn_datablksz /
 237             zfetch_max_distance));
 238         if (zf->zf_numstreams >= max_streams) {
 239                 ZFETCHSTAT_BUMP(zfetchstat_max_streams);
 240                 return;
 241         }
 242
 243         zstream_t *zs = kmem_zalloc(sizeof (*zs), KM_SLEEP);
 244         zs->zs_blkid = blkid;
 245         zs->zs_pf_blkid1 = blkid;
 246         zs->zs_pf_blkid = blkid;
 247         zs->zs_ipf_blkid1 = blkid;
 248         zs->zs_ipf_blkid = blkid;
 249         zs->zs_atime = now;
 250         zs->zs_fetch = zf;
 251         zs->zs_missed = B_FALSE;
 252         zfs_refcount_create(&zs->zs_callers);
 253         zfs_refcount_create(&zs->zs_refs);
 254         /* One reference for zf_stream. */
 255         zfs_refcount_add(&zs->zs_refs, NULL);
 256         zf->zf_numstreams++;
 257         list_insert_head(&zf->zf_stream, zs);
 258 }
 259
 260 static void
 261 dmu_zfetch_stream_done(void *arg, boolean_t io_issued)
 262 {
 263         (void) io_issued;
 264         zstream_t *zs = arg;
 265
 266         if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0)
 267                 dmu_zfetch_stream_fini(zs);
 268 }
 269
 270 /*
 271  * This is the predictive prefetch entry point.  dmu_zfetch_prepare()
 272  * associates dnode access specified with blkid and nblks arguments with
 273  * prefetch stream, predicts further accesses based on that stats and returns
 274  * the stream pointer on success.  That pointer must later be passed to
 275  * dmu_zfetch_run() to initiate the speculative prefetch for the stream and
 276  * release it.  dmu_zfetch() is a wrapper for simple cases when window between
 277  * prediction and prefetch initiation is not needed.
 278  * fetch_data argument specifies whether actual data blocks should be fetched:
 279  *   FALSE -- prefetch only indirect blocks for predicted data blocks;
 280  *   TRUE -- prefetch predicted data blocks plus following indirect blocks.
 281  */
 282 zstream_t *
 283 dmu_zfetch_prepare(zfetch_t *zf, uint64_t blkid, uint64_t nblks,
 284     boolean_t fetch_data, boolean_t have_lock)
 285 {
 286         zstream_t *zs;
 287         int64_t pf_start, ipf_start;
 288         int64_t pf_ahead_blks, max_blks;
 289         int max_dist_blks, pf_nblks, ipf_nblks;
 290         uint64_t end_of_access_blkid, maxblkid;
 291         end_of_access_blkid = blkid + nblks;
 292         spa_t *spa = zf->zf_dnode->dn_objset->os_spa;
 293
 294         if (zfs_prefetch_disable)
 295                 return (NULL);
 296         /*
 297          * If we haven't yet loaded the indirect vdevs' mappings, we
 298          * can only read from blocks that we carefully ensure are on
 299          * concrete vdevs (or previously-loaded indirect vdevs).  So we
 300          * can't allow the predictive prefetcher to attempt reads of other
 301          * blocks (e.g. of the MOS's dnode object).
 302          */
 303         if (!spa_indirect_vdevs_loaded(spa))
 304                 return (NULL);
 305
 306         /*
 307          * As a fast path for small (single-block) files, ignore access
 308          * to the first block.
 309          */
 310         if (!have_lock && blkid == 0)
 311                 return (NULL);
 312
 313         if (!have_lock)
 314                 rw_enter(&zf->zf_dnode->dn_struct_rwlock, RW_READER);
 315
 316         /*
 317          * A fast path for small files for which no prefetch will
 318          * happen.
 319          */
 320         maxblkid = zf->zf_dnode->dn_maxblkid;
 321         if (maxblkid < 2) {
 322                 if (!have_lock)
 323                         rw_exit(&zf->zf_dnode->dn_struct_rwlock);
 324                 return (NULL);
 325         }
 326         mutex_enter(&zf->zf_lock);
 327
 328         /*
 329          * Find matching prefetch stream.  Depending on whether the accesses
 330          * are block-aligned, first block of the new access may either follow
 331          * the last block of the previous access, or be equal to it.
 332          */
 333         for (zs = list_head(&zf->zf_stream); zs != NULL;
 334             zs = list_next(&zf->zf_stream, zs)) {
 335                 if (blkid == zs->zs_blkid) {
 336                         break;
 337                 } else if (blkid + 1 == zs->zs_blkid) {
 338                         blkid++;
 339                         nblks--;
 340                         break;
 341                 }
 342         }
 343
 344         /*
 345          * If the file is ending, remove the matching stream if found.
 346          * If not found then it is too late to create a new one now.
 347          */
 348         if (end_of_access_blkid >= maxblkid) {
 349                 if (zs != NULL)
 350                         dmu_zfetch_stream_remove(zf, zs);
 351                 mutex_exit(&zf->zf_lock);
 352                 if (!have_lock)
 353                         rw_exit(&zf->zf_dnode->dn_struct_rwlock);
 354                 return (NULL);
 355         }
 356
 357         /* Exit if we already prefetched this block before. */
 358         if (nblks == 0) {
 359                 mutex_exit(&zf->zf_lock);
 360                 if (!have_lock)
 361                         rw_exit(&zf->zf_dnode->dn_struct_rwlock);
 362                 return (NULL);
 363         }
 364
 365         if (zs == NULL) {
 366                 /*
 367                  * This access is not part of any existing stream.  Create
 368                  * a new stream for it.
 369                  */
 370                 dmu_zfetch_stream_create(zf, end_of_access_blkid);
 371                 mutex_exit(&zf->zf_lock);
 372                 if (!have_lock)
 373                         rw_exit(&zf->zf_dnode->dn_struct_rwlock);
 374                 ZFETCHSTAT_BUMP(zfetchstat_misses);
 375                 return (NULL);
 376         }
 377
 378         /*
 379          * This access was to a block that we issued a prefetch for on
 380          * behalf of this stream. Issue further prefetches for this stream.
 381          *
 382          * Normally, we start prefetching where we stopped
 383          * prefetching last (zs_pf_blkid).  But when we get our first
 384          * hit on this stream, zs_pf_blkid == zs_blkid, we don't
 385          * want to prefetch the block we just accessed.  In this case,
 386          * start just after the block we just accessed.
 387          */
 388         pf_start = MAX(zs->zs_pf_blkid, end_of_access_blkid);
 389         if (zs->zs_pf_blkid1 < end_of_access_blkid)
 390                 zs->zs_pf_blkid1 = end_of_access_blkid;
 391         if (zs->zs_ipf_blkid1 < end_of_access_blkid)
 392                 zs->zs_ipf_blkid1 = end_of_access_blkid;
 393
 394         /*
 395          * Double our amount of prefetched data, but don't let the
 396          * prefetch get further ahead than zfetch_max_distance.
 397          */
 398         if (fetch_data) {
 399                 max_dist_blks =
 400                     zfetch_max_distance >> zf->zf_dnode->dn_datablkshift;
 401                 /*
 402                  * Previously, we were (zs_pf_blkid - blkid) ahead.  We
 403                  * want to now be double that, so read that amount again,
 404                  * plus the amount we are catching up by (i.e. the amount
 405                  * read just now).
 406                  */
 407                 pf_ahead_blks = zs->zs_pf_blkid - blkid + nblks;
 408                 max_blks = max_dist_blks - (pf_start - end_of_access_blkid);
 409                 pf_nblks = MIN(pf_ahead_blks, max_blks);
 410         } else {
 411                 pf_nblks = 0;
 412         }
 413
 414         zs->zs_pf_blkid = pf_start + pf_nblks;
 415
 416         /*
 417          * Do the same for indirects, starting from where we stopped last,
 418          * or where we will stop reading data blocks (and the indirects
 419          * that point to them).
 420          */
 421         ipf_start = MAX(zs->zs_ipf_blkid, zs->zs_pf_blkid);
 422         max_dist_blks = zfetch_max_idistance >> zf->zf_dnode->dn_datablkshift;
 423         /*
 424          * We want to double our distance ahead of the data prefetch
 425          * (or reader, if we are not prefetching data).  Previously, we
 426          * were (zs_ipf_blkid - blkid) ahead.  To double that, we read
 427          * that amount again, plus the amount we are catching up by
 428          * (i.e. the amount read now + the amount of data prefetched now).
 429          */
 430         pf_ahead_blks = zs->zs_ipf_blkid - blkid + nblks + pf_nblks;
 431         max_blks = max_dist_blks - (ipf_start - zs->zs_pf_blkid);
 432         ipf_nblks = MIN(pf_ahead_blks, max_blks);
 433         zs->zs_ipf_blkid = ipf_start + ipf_nblks;
 434
 435         zs->zs_blkid = end_of_access_blkid;
 436         /* Protect the stream from reclamation. */
 437         zs->zs_atime = gethrtime();
 438         zfs_refcount_add(&zs->zs_refs, NULL);
 439         /* Count concurrent callers. */
 440         zfs_refcount_add(&zs->zs_callers, NULL);
 441         mutex_exit(&zf->zf_lock);
 442
 443         if (!have_lock)
 444                 rw_exit(&zf->zf_dnode->dn_struct_rwlock);
 445
 446         ZFETCHSTAT_BUMP(zfetchstat_hits);
 447         return (zs);
 448 }
 449
 450 void
 451 dmu_zfetch_run(zstream_t *zs, boolean_t missed, boolean_t have_lock)
 452 {
 453         zfetch_t *zf = zs->zs_fetch;
 454         int64_t pf_start, pf_end, ipf_start, ipf_end;
 455         int epbs, issued;
 456
 457         if (missed)
 458                 zs->zs_missed = missed;
 459
 460         /*
 461          * Postpone the prefetch if there are more concurrent callers.
 462          * It happens when multiple requests are waiting for the same
 463          * indirect block.  The last one will run the prefetch for all.
 464          */
 465         if (zfs_refcount_remove(&zs->zs_callers, NULL) != 0) {
 466                 /* Drop reference taken in dmu_zfetch_prepare(). */
 467                 if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0)
 468                         dmu_zfetch_stream_fini(zs);
 469                 return;
 470         }
 471
 472         mutex_enter(&zf->zf_lock);
 473         if (zs->zs_missed) {
 474                 pf_start = zs->zs_pf_blkid1;
 475                 pf_end = zs->zs_pf_blkid1 = zs->zs_pf_blkid;
 476         } else {
 477                 pf_start = pf_end = 0;
 478         }
 479         ipf_start = MAX(zs->zs_pf_blkid1, zs->zs_ipf_blkid1);
 480         ipf_end = zs->zs_ipf_blkid1 = zs->zs_ipf_blkid;
 481         mutex_exit(&zf->zf_lock);
 482         ASSERT3S(pf_start, <=, pf_end);
 483         ASSERT3S(ipf_start, <=, ipf_end);
 484
 485         epbs = zf->zf_dnode->dn_indblkshift - SPA_BLKPTRSHIFT;
 486         ipf_start = P2ROUNDUP(ipf_start, 1 << epbs) >> epbs;
 487         ipf_end = P2ROUNDUP(ipf_end, 1 << epbs) >> epbs;
 488         ASSERT3S(ipf_start, <=, ipf_end);
 489         issued = pf_end - pf_start + ipf_end - ipf_start;
 490         if (issued > 1) {
 491                 /* More references on top of taken in dmu_zfetch_prepare(). */
 492                 for (int i = 0; i < issued - 1; i++)
 493                         zfs_refcount_add(&zs->zs_refs, NULL);
 494         } else if (issued == 0) {
 495                 /* Some other thread has done our work, so drop the ref. */
 496                 if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0)
 497                         dmu_zfetch_stream_fini(zs);
 498                 return;
 499         }
 500
 501         if (!have_lock)
 502                 rw_enter(&zf->zf_dnode->dn_struct_rwlock, RW_READER);
 503
 504         issued = 0;
 505         for (int64_t blk = pf_start; blk < pf_end; blk++) {
 506                 issued += dbuf_prefetch_impl(zf->zf_dnode, 0, blk,
 507                     ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH,
 508                     dmu_zfetch_stream_done, zs);
 509         }
 510         for (int64_t iblk = ipf_start; iblk < ipf_end; iblk++) {
 511                 issued += dbuf_prefetch_impl(zf->zf_dnode, 1, iblk,
 512                     ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH,
 513                     dmu_zfetch_stream_done, zs);
 514         }
 515
 516         if (!have_lock)
 517                 rw_exit(&zf->zf_dnode->dn_struct_rwlock);
 518
 519         if (issued)
 520                 ZFETCHSTAT_ADD(zfetchstat_io_issued, issued);
 521 }
 522
 523 void
 524 dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks, boolean_t fetch_data,
 525     boolean_t missed, boolean_t have_lock)
 526 {
 527         zstream_t *zs;
 528
 529         zs = dmu_zfetch_prepare(zf, blkid, nblks, fetch_data, have_lock);
 530         if (zs)
 531                 dmu_zfetch_run(zs, missed, have_lock);
 532 }
 533
 534 ZFS_MODULE_PARAM(zfs_prefetch, zfs_prefetch_, disable, INT, ZMOD_RW,
 535         "Disable all ZFS prefetching");
 536
 537 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_streams, UINT, ZMOD_RW,
 538         "Max number of streams per zfetch");
 539
 540 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, min_sec_reap, UINT, ZMOD_RW,
 541         "Min time before stream reclaim");
 542
 543 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_distance, UINT, ZMOD_RW,
 544         "Max bytes to prefetch per stream");
 545
 546 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_idistance, UINT, ZMOD_RW,
 547         "Max bytes to prefetch indirects for per stream");
 548
 549 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, array_rd_sz, ULONG, ZMOD_RW,
 550         "Number of bytes in a array_read");