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 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  * I'm against tune-ables, but these should probably exist as tweakable globals
  40  * until we can get this working the way we want it to.
  41  */
  42
  43 int zfs_prefetch_disable = 0;
  44
  45 /* max # of streams per zfetch */
  46 uint32_t        zfetch_max_streams = 8;
  47 /* min time before stream reclaim */
  48 uint32_t        zfetch_min_sec_reap = 2;
  49 /* max number of blocks to fetch at a time */
  50 uint32_t        zfetch_block_cap = 256;
  51 /* number of bytes in a array_read at which we stop prefetching (1Mb) */
  52 uint64_t        zfetch_array_rd_sz = 1024 * 1024;
  53
  54 SYSCTL_DECL(_vfs_zfs);
  55 SYSCTL_INT(_vfs_zfs, OID_AUTO, prefetch_disable, CTLFLAG_RW,
  56     &zfs_prefetch_disable, 0, "Disable prefetch");
  57 SYSCTL_NODE(_vfs_zfs, OID_AUTO, zfetch, CTLFLAG_RW, 0, "ZFS ZFETCH");
  58 TUNABLE_INT("vfs.zfs.zfetch.max_streams", &zfetch_max_streams);
  59 SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, max_streams, CTLFLAG_RW,
  60     &zfetch_max_streams, 0, "Max # of streams per zfetch");
  61 TUNABLE_INT("vfs.zfs.zfetch.min_sec_reap", &zfetch_min_sec_reap);
  62 SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, min_sec_reap, CTLFLAG_RDTUN,
  63     &zfetch_min_sec_reap, 0, "Min time before stream reclaim");
  64 TUNABLE_INT("vfs.zfs.zfetch.block_cap", &zfetch_block_cap);
  65 SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, block_cap, CTLFLAG_RDTUN,
  66     &zfetch_block_cap, 0, "Max number of blocks to fetch at a time");
  67 TUNABLE_QUAD("vfs.zfs.zfetch.array_rd_sz", &zfetch_array_rd_sz);
  68 SYSCTL_UQUAD(_vfs_zfs_zfetch, OID_AUTO, array_rd_sz, CTLFLAG_RDTUN,
  69     &zfetch_array_rd_sz, 0,
  70     "Number of bytes in a array_read at which we stop prefetching");
  71
  72 /* forward decls for static routines */
  73 static boolean_t        dmu_zfetch_colinear(zfetch_t *, zstream_t *);
  74 static void             dmu_zfetch_dofetch(zfetch_t *, zstream_t *);
  75 static uint64_t         dmu_zfetch_fetch(dnode_t *, uint64_t, uint64_t);
  76 static uint64_t         dmu_zfetch_fetchsz(dnode_t *, uint64_t, uint64_t);
  77 static boolean_t        dmu_zfetch_find(zfetch_t *, zstream_t *, int);
  78 static int              dmu_zfetch_stream_insert(zfetch_t *, zstream_t *);
  79 static zstream_t        *dmu_zfetch_stream_reclaim(zfetch_t *);
  80 static void             dmu_zfetch_stream_remove(zfetch_t *, zstream_t *);
  81 static int              dmu_zfetch_streams_equal(zstream_t *, zstream_t *);
  82
  83 typedef struct zfetch_stats {
  84         kstat_named_t zfetchstat_hits;
  85         kstat_named_t zfetchstat_misses;
  86         kstat_named_t zfetchstat_colinear_hits;
  87         kstat_named_t zfetchstat_colinear_misses;
  88         kstat_named_t zfetchstat_stride_hits;
  89         kstat_named_t zfetchstat_stride_misses;
  90         kstat_named_t zfetchstat_reclaim_successes;
  91         kstat_named_t zfetchstat_reclaim_failures;
  92         kstat_named_t zfetchstat_stream_resets;
  93         kstat_named_t zfetchstat_stream_noresets;
  94         kstat_named_t zfetchstat_bogus_streams;
  95 } zfetch_stats_t;
  96
  97 static zfetch_stats_t zfetch_stats = {
  98         { "hits",                       KSTAT_DATA_UINT64 },
  99         { "misses",                     KSTAT_DATA_UINT64 },
 100         { "colinear_hits",              KSTAT_DATA_UINT64 },
 101         { "colinear_misses",            KSTAT_DATA_UINT64 },
 102         { "stride_hits",                KSTAT_DATA_UINT64 },
 103         { "stride_misses",              KSTAT_DATA_UINT64 },
 104         { "reclaim_successes",          KSTAT_DATA_UINT64 },
 105         { "reclaim_failures",           KSTAT_DATA_UINT64 },
 106         { "streams_resets",             KSTAT_DATA_UINT64 },
 107         { "streams_noresets",           KSTAT_DATA_UINT64 },
 108         { "bogus_streams",              KSTAT_DATA_UINT64 },
 109 };
 110
 111 #define ZFETCHSTAT_INCR(stat, val) \
 112         atomic_add_64(&zfetch_stats.stat.value.ui64, (val));
 113
 114 #define ZFETCHSTAT_BUMP(stat)           ZFETCHSTAT_INCR(stat, 1);
 115
 116 kstat_t         *zfetch_ksp;
 117
 118 /*
 119  * Given a zfetch structure and a zstream structure, determine whether the
 120  * blocks to be read are part of a co-linear pair of existing prefetch
 121  * streams.  If a set is found, coalesce the streams, removing one, and
 122  * configure the prefetch so it looks for a strided access pattern.
 123  *
 124  * In other words: if we find two sequential access streams that are
 125  * the same length and distance N appart, and this read is N from the
 126  * last stream, then we are probably in a strided access pattern.  So
 127  * combine the two sequential streams into a single strided stream.
 128  *
 129  * Returns whether co-linear streams were found.
 130  */
 131 static boolean_t
 132 dmu_zfetch_colinear(zfetch_t *zf, zstream_t *zh)
 133 {
 134         zstream_t       *z_walk;
 135         zstream_t       *z_comp;
 136
 137         if (! rw_tryenter(&zf->zf_rwlock, RW_WRITER))
 138                 return (0);
 139
 140         if (zh == NULL) {
 141                 rw_exit(&zf->zf_rwlock);
 142                 return (0);
 143         }
 144
 145         for (z_walk = list_head(&zf->zf_stream); z_walk;
 146             z_walk = list_next(&zf->zf_stream, z_walk)) {
 147                 for (z_comp = list_next(&zf->zf_stream, z_walk); z_comp;
 148                     z_comp = list_next(&zf->zf_stream, z_comp)) {
 149                         int64_t         diff;
 150
 151                         if (z_walk->zst_len != z_walk->zst_stride ||
 152                             z_comp->zst_len != z_comp->zst_stride) {
 153                                 continue;
 154                         }
 155
 156                         diff = z_comp->zst_offset - z_walk->zst_offset;
 157                         if (z_comp->zst_offset + diff == zh->zst_offset) {
 158                                 z_walk->zst_offset = zh->zst_offset;
 159                                 z_walk->zst_direction = diff < 0 ? -1 : 1;
 160                                 z_walk->zst_stride =
 161                                     diff * z_walk->zst_direction;
 162                                 z_walk->zst_ph_offset =
 163                                     zh->zst_offset + z_walk->zst_stride;
 164                                 dmu_zfetch_stream_remove(zf, z_comp);
 165                                 mutex_destroy(&z_comp->zst_lock);
 166                                 kmem_free(z_comp, sizeof (zstream_t));
 167
 168                                 dmu_zfetch_dofetch(zf, z_walk);
 169
 170                                 rw_exit(&zf->zf_rwlock);
 171                                 return (1);
 172                         }
 173
 174                         diff = z_walk->zst_offset - z_comp->zst_offset;
 175                         if (z_walk->zst_offset + diff == zh->zst_offset) {
 176                                 z_walk->zst_offset = zh->zst_offset;
 177                                 z_walk->zst_direction = diff < 0 ? -1 : 1;
 178                                 z_walk->zst_stride =
 179                                     diff * z_walk->zst_direction;
 180                                 z_walk->zst_ph_offset =
 181                                     zh->zst_offset + z_walk->zst_stride;
 182                                 dmu_zfetch_stream_remove(zf, z_comp);
 183                                 mutex_destroy(&z_comp->zst_lock);
 184                                 kmem_free(z_comp, sizeof (zstream_t));
 185
 186                                 dmu_zfetch_dofetch(zf, z_walk);
 187
 188                                 rw_exit(&zf->zf_rwlock);
 189                                 return (1);
 190                         }
 191                 }
 192         }
 193
 194         rw_exit(&zf->zf_rwlock);
 195         return (0);
 196 }
 197
 198 /*
 199  * Given a zstream_t, determine the bounds of the prefetch.  Then call the
 200  * routine that actually prefetches the individual blocks.
 201  */
 202 static void
 203 dmu_zfetch_dofetch(zfetch_t *zf, zstream_t *zs)
 204 {
 205         uint64_t        prefetch_tail;
 206         uint64_t        prefetch_limit;
 207         uint64_t        prefetch_ofst;
 208         uint64_t        prefetch_len;
 209         uint64_t        blocks_fetched;
 210
 211         zs->zst_stride = MAX((int64_t)zs->zst_stride, zs->zst_len);
 212         zs->zst_cap = MIN(zfetch_block_cap, 2 * zs->zst_cap);
 213
 214         prefetch_tail = MAX((int64_t)zs->zst_ph_offset,
 215             (int64_t)(zs->zst_offset + zs->zst_stride));
 216         /*
 217          * XXX: use a faster division method?
 218          */
 219         prefetch_limit = zs->zst_offset + zs->zst_len +
 220             (zs->zst_cap * zs->zst_stride) / zs->zst_len;
 221
 222         while (prefetch_tail < prefetch_limit) {
 223                 prefetch_ofst = zs->zst_offset + zs->zst_direction *
 224                     (prefetch_tail - zs->zst_offset);
 225
 226                 prefetch_len = zs->zst_len;
 227
 228                 /*
 229                  * Don't prefetch beyond the end of the file, if working
 230                  * backwards.
 231                  */
 232                 if ((zs->zst_direction == ZFETCH_BACKWARD) &&
 233                     (prefetch_ofst > prefetch_tail)) {
 234                         prefetch_len += prefetch_ofst;
 235                         prefetch_ofst = 0;
 236                 }
 237
 238                 /* don't prefetch more than we're supposed to */
 239                 if (prefetch_len > zs->zst_len)
 240                         break;
 241
 242                 blocks_fetched = dmu_zfetch_fetch(zf->zf_dnode,
 243                     prefetch_ofst, zs->zst_len);
 244
 245                 prefetch_tail += zs->zst_stride;
 246                 /* stop if we've run out of stuff to prefetch */
 247                 if (blocks_fetched < zs->zst_len)
 248                         break;
 249         }
 250         zs->zst_ph_offset = prefetch_tail;
 251         zs->zst_last = ddi_get_lbolt();
 252 }
 253
 254 void
 255 zfetch_init(void)
 256 {
 257
 258         zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc",
 259             KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t),
 260             KSTAT_FLAG_VIRTUAL);
 261
 262         if (zfetch_ksp != NULL) {
 263                 zfetch_ksp->ks_data = &zfetch_stats;
 264                 kstat_install(zfetch_ksp);
 265         }
 266 }
 267
 268 void
 269 zfetch_fini(void)
 270 {
 271         if (zfetch_ksp != NULL) {
 272                 kstat_delete(zfetch_ksp);
 273                 zfetch_ksp = NULL;
 274         }
 275 }
 276
 277 /*
 278  * This takes a pointer to a zfetch structure and a dnode.  It performs the
 279  * necessary setup for the zfetch structure, grokking data from the
 280  * associated dnode.
 281  */
 282 void
 283 dmu_zfetch_init(zfetch_t *zf, dnode_t *dno)
 284 {
 285         if (zf == NULL) {
 286                 return;
 287         }
 288
 289         zf->zf_dnode = dno;
 290         zf->zf_stream_cnt = 0;
 291         zf->zf_alloc_fail = 0;
 292
 293         list_create(&zf->zf_stream, sizeof (zstream_t),
 294             offsetof(zstream_t, zst_node));
 295
 296         rw_init(&zf->zf_rwlock, NULL, RW_DEFAULT, NULL);
 297 }
 298
 299 /*
 300  * This function computes the actual size, in blocks, that can be prefetched,
 301  * and fetches it.
 302  */
 303 static uint64_t
 304 dmu_zfetch_fetch(dnode_t *dn, uint64_t blkid, uint64_t nblks)
 305 {
 306         uint64_t        fetchsz;
 307         uint64_t        i;
 308
 309         fetchsz = dmu_zfetch_fetchsz(dn, blkid, nblks);
 310
 311         for (i = 0; i < fetchsz; i++) {
 312                 dbuf_prefetch(dn, blkid + i, ZIO_PRIORITY_ASYNC_READ);
 313         }
 314
 315         return (fetchsz);
 316 }
 317
 318 /*
 319  * this function returns the number of blocks that would be prefetched, based
 320  * upon the supplied dnode, blockid, and nblks.  This is used so that we can
 321  * update streams in place, and then prefetch with their old value after the
 322  * fact.  This way, we can delay the prefetch, but subsequent accesses to the
 323  * stream won't result in the same data being prefetched multiple times.
 324  */
 325 static uint64_t
 326 dmu_zfetch_fetchsz(dnode_t *dn, uint64_t blkid, uint64_t nblks)
 327 {
 328         uint64_t        fetchsz;
 329
 330         if (blkid > dn->dn_maxblkid) {
 331                 return (0);
 332         }
 333
 334         /* compute fetch size */
 335         if (blkid + nblks + 1 > dn->dn_maxblkid) {
 336                 fetchsz = (dn->dn_maxblkid - blkid) + 1;
 337                 ASSERT(blkid + fetchsz - 1 <= dn->dn_maxblkid);
 338         } else {
 339                 fetchsz = nblks;
 340         }
 341
 342
 343         return (fetchsz);
 344 }
 345
 346 /*
 347  * given a zfetch and a zstream structure, see if there is an associated zstream
 348  * for this block read.  If so, it starts a prefetch for the stream it
 349  * located and returns true, otherwise it returns false
 350  */
 351 static boolean_t
 352 dmu_zfetch_find(zfetch_t *zf, zstream_t *zh, int prefetched)
 353 {
 354         zstream_t       *zs;
 355         int64_t         diff;
 356         int             reset = !prefetched;
 357         int             rc = 0;
 358
 359         if (zh == NULL)
 360                 return (0);
 361
 362         /*
 363          * XXX: This locking strategy is a bit coarse; however, it's impact has
 364          * yet to be tested.  If this turns out to be an issue, it can be
 365          * modified in a number of different ways.
 366          */
 367
 368         rw_enter(&zf->zf_rwlock, RW_READER);
 369 top:
 370
 371         for (zs = list_head(&zf->zf_stream); zs;
 372             zs = list_next(&zf->zf_stream, zs)) {
 373
 374                 /*
 375                  * XXX - should this be an assert?
 376                  */
 377                 if (zs->zst_len == 0) {
 378                         /* bogus stream */
 379                         ZFETCHSTAT_BUMP(zfetchstat_bogus_streams);
 380                         continue;
 381                 }
 382
 383                 /*
 384                  * We hit this case when we are in a strided prefetch stream:
 385                  * we will read "len" blocks before "striding".
 386                  */
 387                 if (zh->zst_offset >= zs->zst_offset &&
 388                     zh->zst_offset < zs->zst_offset + zs->zst_len) {
 389                         if (prefetched) {
 390                                 /* already fetched */
 391                                 ZFETCHSTAT_BUMP(zfetchstat_stride_hits);
 392                                 rc = 1;
 393                                 goto out;
 394                         } else {
 395                                 ZFETCHSTAT_BUMP(zfetchstat_stride_misses);
 396                         }
 397                 }
 398
 399                 /*
 400                  * This is the forward sequential read case: we increment
 401                  * len by one each time we hit here, so we will enter this
 402                  * case on every read.
 403                  */
 404                 if (zh->zst_offset == zs->zst_offset + zs->zst_len) {
 405
 406                         reset = !prefetched && zs->zst_len > 1;
 407
 408                         if (mutex_tryenter(&zs->zst_lock) == 0) {
 409                                 rc = 1;
 410                                 goto out;
 411                         }
 412
 413                         if (zh->zst_offset != zs->zst_offset + zs->zst_len) {
 414                                 mutex_exit(&zs->zst_lock);
 415                                 goto top;
 416                         }
 417                         zs->zst_len += zh->zst_len;
 418                         diff = zs->zst_len - zfetch_block_cap;
 419                         if (diff > 0) {
 420                                 zs->zst_offset += diff;
 421                                 zs->zst_len = zs->zst_len > diff ?
 422                                     zs->zst_len - diff : 0;
 423                         }
 424                         zs->zst_direction = ZFETCH_FORWARD;
 425
 426                         break;
 427
 428                 /*
 429                  * Same as above, but reading backwards through the file.
 430                  */
 431                 } else if (zh->zst_offset == zs->zst_offset - zh->zst_len) {
 432                         /* backwards sequential access */
 433
 434                         reset = !prefetched && zs->zst_len > 1;
 435
 436                         if (mutex_tryenter(&zs->zst_lock) == 0) {
 437                                 rc = 1;
 438                                 goto out;
 439                         }
 440
 441                         if (zh->zst_offset != zs->zst_offset - zh->zst_len) {
 442                                 mutex_exit(&zs->zst_lock);
 443                                 goto top;
 444                         }
 445
 446                         zs->zst_offset = zs->zst_offset > zh->zst_len ?
 447                             zs->zst_offset - zh->zst_len : 0;
 448                         zs->zst_ph_offset = zs->zst_ph_offset > zh->zst_len ?
 449                             zs->zst_ph_offset - zh->zst_len : 0;
 450                         zs->zst_len += zh->zst_len;
 451
 452                         diff = zs->zst_len - zfetch_block_cap;
 453                         if (diff > 0) {
 454                                 zs->zst_ph_offset = zs->zst_ph_offset > diff ?
 455                                     zs->zst_ph_offset - diff : 0;
 456                                 zs->zst_len = zs->zst_len > diff ?
 457                                     zs->zst_len - diff : zs->zst_len;
 458                         }
 459                         zs->zst_direction = ZFETCH_BACKWARD;
 460
 461                         break;
 462
 463                 } else if ((zh->zst_offset - zs->zst_offset - zs->zst_stride <
 464                     zs->zst_len) && (zs->zst_len != zs->zst_stride)) {
 465                         /* strided forward access */
 466
 467                         if (mutex_tryenter(&zs->zst_lock) == 0) {
 468                                 rc = 1;
 469                                 goto out;
 470                         }
 471
 472                         if ((zh->zst_offset - zs->zst_offset - zs->zst_stride >=
 473                             zs->zst_len) || (zs->zst_len == zs->zst_stride)) {
 474                                 mutex_exit(&zs->zst_lock);
 475                                 goto top;
 476                         }
 477
 478                         zs->zst_offset += zs->zst_stride;
 479                         zs->zst_direction = ZFETCH_FORWARD;
 480
 481                         break;
 482
 483                 } else if ((zh->zst_offset - zs->zst_offset + zs->zst_stride <
 484                     zs->zst_len) && (zs->zst_len != zs->zst_stride)) {
 485                         /* strided reverse access */
 486
 487                         if (mutex_tryenter(&zs->zst_lock) == 0) {
 488                                 rc = 1;
 489                                 goto out;
 490                         }
 491
 492                         if ((zh->zst_offset - zs->zst_offset + zs->zst_stride >=
 493                             zs->zst_len) || (zs->zst_len == zs->zst_stride)) {
 494                                 mutex_exit(&zs->zst_lock);
 495                                 goto top;
 496                         }
 497
 498                         zs->zst_offset = zs->zst_offset > zs->zst_stride ?
 499                             zs->zst_offset - zs->zst_stride : 0;
 500                         zs->zst_ph_offset = (zs->zst_ph_offset >
 501                             (2 * zs->zst_stride)) ?
 502                             (zs->zst_ph_offset - (2 * zs->zst_stride)) : 0;
 503                         zs->zst_direction = ZFETCH_BACKWARD;
 504
 505                         break;
 506                 }
 507         }
 508
 509         if (zs) {
 510                 if (reset) {
 511                         zstream_t *remove = zs;
 512
 513                         ZFETCHSTAT_BUMP(zfetchstat_stream_resets);
 514                         rc = 0;
 515                         mutex_exit(&zs->zst_lock);
 516                         rw_exit(&zf->zf_rwlock);
 517                         rw_enter(&zf->zf_rwlock, RW_WRITER);
 518                         /*
 519                          * Relocate the stream, in case someone removes
 520                          * it while we were acquiring the WRITER lock.
 521                          */
 522                         for (zs = list_head(&zf->zf_stream); zs;
 523                             zs = list_next(&zf->zf_stream, zs)) {
 524                                 if (zs == remove) {
 525                                         dmu_zfetch_stream_remove(zf, zs);
 526                                         mutex_destroy(&zs->zst_lock);
 527                                         kmem_free(zs, sizeof (zstream_t));
 528                                         break;
 529                                 }
 530                         }
 531                 } else {
 532                         ZFETCHSTAT_BUMP(zfetchstat_stream_noresets);
 533                         rc = 1;
 534                         dmu_zfetch_dofetch(zf, zs);
 535                         mutex_exit(&zs->zst_lock);
 536                 }
 537         }
 538 out:
 539         rw_exit(&zf->zf_rwlock);
 540         return (rc);
 541 }
 542
 543 /*
 544  * Clean-up state associated with a zfetch structure.  This frees allocated
 545  * structure members, empties the zf_stream tree, and generally makes things
 546  * nice.  This doesn't free the zfetch_t itself, that's left to the caller.
 547  */
 548 void
 549 dmu_zfetch_rele(zfetch_t *zf)
 550 {
 551         zstream_t       *zs;
 552         zstream_t       *zs_next;
 553
 554         ASSERT(!RW_LOCK_HELD(&zf->zf_rwlock));
 555
 556         for (zs = list_head(&zf->zf_stream); zs; zs = zs_next) {
 557                 zs_next = list_next(&zf->zf_stream, zs);
 558
 559                 list_remove(&zf->zf_stream, zs);
 560                 mutex_destroy(&zs->zst_lock);
 561                 kmem_free(zs, sizeof (zstream_t));
 562         }
 563         list_destroy(&zf->zf_stream);
 564         rw_destroy(&zf->zf_rwlock);
 565
 566         zf->zf_dnode = NULL;
 567 }
 568
 569 /*
 570  * Given a zfetch and zstream structure, insert the zstream structure into the
 571  * AVL tree contained within the zfetch structure.  Peform the appropriate
 572  * book-keeping.  It is possible that another thread has inserted a stream which
 573  * matches one that we are about to insert, so we must be sure to check for this
 574  * case.  If one is found, return failure, and let the caller cleanup the
 575  * duplicates.
 576  */
 577 static int
 578 dmu_zfetch_stream_insert(zfetch_t *zf, zstream_t *zs)
 579 {
 580         zstream_t       *zs_walk;
 581         zstream_t       *zs_next;
 582
 583         ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
 584
 585         for (zs_walk = list_head(&zf->zf_stream); zs_walk; zs_walk = zs_next) {
 586                 zs_next = list_next(&zf->zf_stream, zs_walk);
 587
 588                 if (dmu_zfetch_streams_equal(zs_walk, zs)) {
 589                         return (0);
 590                 }
 591         }
 592
 593         list_insert_head(&zf->zf_stream, zs);
 594         zf->zf_stream_cnt++;
 595         return (1);
 596 }
 597
 598
 599 /*
 600  * Walk the list of zstreams in the given zfetch, find an old one (by time), and
 601  * reclaim it for use by the caller.
 602  */
 603 static zstream_t *
 604 dmu_zfetch_stream_reclaim(zfetch_t *zf)
 605 {
 606         zstream_t       *zs;
 607         clock_t         ticks;
 608
 609         ticks = zfetch_min_sec_reap * hz;
 610         if (! rw_tryenter(&zf->zf_rwlock, RW_WRITER))
 611                 return (0);
 612
 613         for (zs = list_head(&zf->zf_stream); zs;
 614             zs = list_next(&zf->zf_stream, zs)) {
 615
 616                 if (ddi_get_lbolt() - zs->zst_last > ticks)
 617                         break;
 618         }
 619
 620         if (zs) {
 621                 dmu_zfetch_stream_remove(zf, zs);
 622                 mutex_destroy(&zs->zst_lock);
 623                 bzero(zs, sizeof (zstream_t));
 624         } else {
 625                 zf->zf_alloc_fail++;
 626         }
 627         rw_exit(&zf->zf_rwlock);
 628
 629         return (zs);
 630 }
 631
 632 /*
 633  * Given a zfetch and zstream structure, remove the zstream structure from its
 634  * container in the zfetch structure.  Perform the appropriate book-keeping.
 635  */
 636 static void
 637 dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs)
 638 {
 639         ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
 640
 641         list_remove(&zf->zf_stream, zs);
 642         zf->zf_stream_cnt--;
 643 }
 644
 645 static int
 646 dmu_zfetch_streams_equal(zstream_t *zs1, zstream_t *zs2)
 647 {
 648         if (zs1->zst_offset != zs2->zst_offset)
 649                 return (0);
 650
 651         if (zs1->zst_len != zs2->zst_len)
 652                 return (0);
 653
 654         if (zs1->zst_stride != zs2->zst_stride)
 655                 return (0);
 656
 657         if (zs1->zst_ph_offset != zs2->zst_ph_offset)
 658                 return (0);
 659
 660         if (zs1->zst_cap != zs2->zst_cap)
 661                 return (0);
 662
 663         if (zs1->zst_direction != zs2->zst_direction)
 664                 return (0);
 665
 666         return (1);
 667 }
 668
 669 /*
 670  * This is the prefetch entry point.  It calls all of the other dmu_zfetch
 671  * routines to create, delete, find, or operate upon prefetch streams.
 672  */
 673 void
 674 dmu_zfetch(zfetch_t *zf, uint64_t offset, uint64_t size, int prefetched)
 675 {
 676         zstream_t       zst;
 677         zstream_t       *newstream;
 678         boolean_t       fetched;
 679         int             inserted;
 680         unsigned int    blkshft;
 681         uint64_t        blksz;
 682
 683         if (zfs_prefetch_disable)
 684                 return;
 685
 686         /* files that aren't ln2 blocksz are only one block -- nothing to do */
 687         if (!zf->zf_dnode->dn_datablkshift)
 688                 return;
 689
 690         /* convert offset and size, into blockid and nblocks */
 691         blkshft = zf->zf_dnode->dn_datablkshift;
 692         blksz = (1 << blkshft);
 693
 694         bzero(&zst, sizeof (zstream_t));
 695         zst.zst_offset = offset >> blkshft;
 696         zst.zst_len = (P2ROUNDUP(offset + size, blksz) -
 697             P2ALIGN(offset, blksz)) >> blkshft;
 698
 699         fetched = dmu_zfetch_find(zf, &zst, prefetched);
 700         if (fetched) {
 701                 ZFETCHSTAT_BUMP(zfetchstat_hits);
 702         } else {
 703                 ZFETCHSTAT_BUMP(zfetchstat_misses);
 704                 fetched = dmu_zfetch_colinear(zf, &zst);
 705                 if (fetched) {
 706                         ZFETCHSTAT_BUMP(zfetchstat_colinear_hits);
 707                 } else {
 708                         ZFETCHSTAT_BUMP(zfetchstat_colinear_misses);
 709                 }
 710         }
 711
 712         if (!fetched) {
 713                 newstream = dmu_zfetch_stream_reclaim(zf);
 714
 715                 /*
 716                  * we still couldn't find a stream, drop the lock, and allocate
 717                  * one if possible.  Otherwise, give up and go home.
 718                  */
 719                 if (newstream) {
 720                         ZFETCHSTAT_BUMP(zfetchstat_reclaim_successes);
 721                 } else {
 722                         uint64_t        maxblocks;
 723                         uint32_t        max_streams;
 724                         uint32_t        cur_streams;
 725
 726                         ZFETCHSTAT_BUMP(zfetchstat_reclaim_failures);
 727                         cur_streams = zf->zf_stream_cnt;
 728                         maxblocks = zf->zf_dnode->dn_maxblkid;
 729
 730                         max_streams = MIN(zfetch_max_streams,
 731                             (maxblocks / zfetch_block_cap));
 732                         if (max_streams == 0) {
 733                                 max_streams++;
 734                         }
 735
 736                         if (cur_streams >= max_streams) {
 737                                 return;
 738                         }
 739                         newstream = kmem_zalloc(sizeof (zstream_t), KM_SLEEP);
 740                 }
 741
 742                 newstream->zst_offset = zst.zst_offset;
 743                 newstream->zst_len = zst.zst_len;
 744                 newstream->zst_stride = zst.zst_len;
 745                 newstream->zst_ph_offset = zst.zst_len + zst.zst_offset;
 746                 newstream->zst_cap = zst.zst_len;
 747                 newstream->zst_direction = ZFETCH_FORWARD;
 748                 newstream->zst_last = ddi_get_lbolt();
 749
 750                 mutex_init(&newstream->zst_lock, NULL, MUTEX_DEFAULT, NULL);
 751
 752                 rw_enter(&zf->zf_rwlock, RW_WRITER);
 753                 inserted = dmu_zfetch_stream_insert(zf, newstream);
 754                 rw_exit(&zf->zf_rwlock);
 755
 756                 if (!inserted) {
 757                         mutex_destroy(&newstream->zst_lock);
 758                         kmem_free(newstream, sizeof (zstream_t));
 759                 }
 760         }
 761 }