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 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 typedef struct zfetch_stats { 58 kstat_named_t zfetchstat_hits; 59 kstat_named_t zfetchstat_misses; 60 kstat_named_t zfetchstat_max_streams; 61 kstat_named_t zfetchstat_max_completion_us; 62 kstat_named_t zfetchstat_last_completion_us; 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 { "max_completion_us", KSTAT_DATA_UINT64 }, 71 { "last_completion_us", KSTAT_DATA_UINT64 }, 72 { "io_issued", KSTAT_DATA_UINT64 }, 73 }; 74 75 #define ZFETCHSTAT_BUMP(stat) \ 76 atomic_inc_64(&zfetch_stats.stat.value.ui64) 77 #define ZFETCHSTAT_ADD(stat, val) \ 78 atomic_add_64(&zfetch_stats.stat.value.ui64, val) 79 #define ZFETCHSTAT_SET(stat, val) \ 80 zfetch_stats.stat.value.ui64 = val 81 #define ZFETCHSTAT_GET(stat) \ 82 zfetch_stats.stat.value.ui64 83 84 85 kstat_t *zfetch_ksp; 86 87 void 88 zfetch_init(void) 89 { 90 zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc", 91 KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t), 92 KSTAT_FLAG_VIRTUAL); 93 94 if (zfetch_ksp != NULL) { 95 zfetch_ksp->ks_data = &zfetch_stats; 96 kstat_install(zfetch_ksp); 97 } 98 } 99 100 void 101 zfetch_fini(void) 102 { 103 if (zfetch_ksp != NULL) { 104 kstat_delete(zfetch_ksp); 105 zfetch_ksp = NULL; 106 } 107 } 108 109 /* 110 * This takes a pointer to a zfetch structure and a dnode. It performs the 111 * necessary setup for the zfetch structure, grokking data from the 112 * associated dnode. 113 */ 114 void 115 dmu_zfetch_init(zfetch_t *zf, dnode_t *dno) 116 { 117 if (zf == NULL) 118 return; 119 zf->zf_dnode = dno; 120 zf->zf_numstreams = 0; 121 122 list_create(&zf->zf_stream, sizeof (zstream_t), 123 offsetof(zstream_t, zs_node)); 124 125 rw_init(&zf->zf_rwlock, NULL, RW_DEFAULT, NULL); 126 } 127 128 static void 129 dmu_zfetch_stream_fini(zstream_t *zs) 130 { 131 mutex_destroy(&zs->zs_lock); 132 kmem_free(zs, sizeof (*zs)); 133 } 134 135 static void 136 dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs) 137 { 138 ASSERT(RW_WRITE_HELD(&zf->zf_rwlock)); 139 list_remove(&zf->zf_stream, zs); 140 dmu_zfetch_stream_fini(zs); 141 zf->zf_numstreams--; 142 } 143 144 static void 145 dmu_zfetch_stream_orphan(zfetch_t *zf, zstream_t *zs) 146 { 147 ASSERT(RW_WRITE_HELD(&zf->zf_rwlock)); 148 list_remove(&zf->zf_stream, zs); 149 zs->zs_fetch = NULL; 150 zf->zf_numstreams--; 151 } 152 153 /* 154 * Clean-up state associated with a zfetch structure (e.g. destroy the 155 * streams). This doesn't free the zfetch_t itself, that's left to the caller. 156 */ 157 void 158 dmu_zfetch_fini(zfetch_t *zf) 159 { 160 zstream_t *zs; 161 162 ASSERT(!RW_LOCK_HELD(&zf->zf_rwlock)); 163 164 rw_enter(&zf->zf_rwlock, RW_WRITER); 165 while ((zs = list_head(&zf->zf_stream)) != NULL) { 166 if (zfs_refcount_count(&zs->zs_blocks) != 0) 167 dmu_zfetch_stream_orphan(zf, zs); 168 else 169 dmu_zfetch_stream_remove(zf, zs); 170 } 171 rw_exit(&zf->zf_rwlock); 172 list_destroy(&zf->zf_stream); 173 rw_destroy(&zf->zf_rwlock); 174 175 zf->zf_dnode = NULL; 176 } 177 178 /* 179 * If there aren't too many streams already, create a new stream. 180 * The "blkid" argument is the next block that we expect this stream to access. 181 * While we're here, clean up old streams (which haven't been 182 * accessed for at least zfetch_min_sec_reap seconds). 183 */ 184 static void 185 dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid) 186 { 187 zstream_t *zs_next; 188 hrtime_t now = gethrtime(); 189 190 ASSERT(RW_WRITE_HELD(&zf->zf_rwlock)); 191 192 /* 193 * Clean up old streams. 194 */ 195 for (zstream_t *zs = list_head(&zf->zf_stream); 196 zs != NULL; zs = zs_next) { 197 zs_next = list_next(&zf->zf_stream, zs); 198 /* 199 * Skip gethrtime() call if there are still references 200 */ 201 if (zfs_refcount_count(&zs->zs_blocks) != 0) 202 continue; 203 if (((now - zs->zs_atime) / NANOSEC) > 204 zfetch_min_sec_reap) 205 dmu_zfetch_stream_remove(zf, zs); 206 } 207 208 /* 209 * The maximum number of streams is normally zfetch_max_streams, 210 * but for small files we lower it such that it's at least possible 211 * for all the streams to be non-overlapping. 212 * 213 * If we are already at the maximum number of streams for this file, 214 * even after removing old streams, then don't create this stream. 215 */ 216 uint32_t max_streams = MAX(1, MIN(zfetch_max_streams, 217 zf->zf_dnode->dn_maxblkid * zf->zf_dnode->dn_datablksz / 218 zfetch_max_distance)); 219 if (zf->zf_numstreams >= max_streams) { 220 ZFETCHSTAT_BUMP(zfetchstat_max_streams); 221 return; 222 } 223 224 zstream_t *zs = kmem_zalloc(sizeof (*zs), KM_SLEEP); 225 zs->zs_blkid = blkid; 226 zs->zs_pf_blkid = blkid; 227 zs->zs_ipf_blkid = blkid; 228 zs->zs_atime = now; 229 zs->zs_fetch = zf; 230 zfs_refcount_create(&zs->zs_blocks); 231 mutex_init(&zs->zs_lock, NULL, MUTEX_DEFAULT, NULL); 232 zf->zf_numstreams++; 233 list_insert_head(&zf->zf_stream, zs); 234 } 235 236 static void 237 dmu_zfetch_stream_done(void *arg, boolean_t io_issued) 238 { 239 zstream_t *zs = arg; 240 241 if (zs->zs_start_time && io_issued) { 242 hrtime_t now = gethrtime(); 243 hrtime_t delta = NSEC2USEC(now - zs->zs_start_time); 244 245 zs->zs_start_time = 0; 246 ZFETCHSTAT_SET(zfetchstat_last_completion_us, delta); 247 if (delta > ZFETCHSTAT_GET(zfetchstat_max_completion_us)) 248 ZFETCHSTAT_SET(zfetchstat_max_completion_us, delta); 249 } 250 251 if (zfs_refcount_remove(&zs->zs_blocks, NULL) != 0) 252 return; 253 254 /* 255 * The parent fetch structure has gone away 256 */ 257 if (zs->zs_fetch == NULL) 258 dmu_zfetch_stream_fini(zs); 259 } 260 261 /* 262 * This is the predictive prefetch entry point. It associates dnode access 263 * specified with blkid and nblks arguments with prefetch stream, predicts 264 * further accesses based on that stats and initiates speculative prefetch. 265 * fetch_data argument specifies whether actual data blocks should be fetched: 266 * FALSE -- prefetch only indirect blocks for predicted data blocks; 267 * TRUE -- prefetch predicted data blocks plus following indirect blocks. 268 */ 269 void 270 dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks, boolean_t fetch_data, 271 boolean_t have_lock) 272 { 273 zstream_t *zs; 274 int64_t pf_start, ipf_start, ipf_istart, ipf_iend; 275 int64_t pf_ahead_blks, max_blks; 276 int epbs, max_dist_blks, pf_nblks, ipf_nblks, issued; 277 uint64_t end_of_access_blkid = blkid + nblks; 278 spa_t *spa = zf->zf_dnode->dn_objset->os_spa; 279 280 if (zfs_prefetch_disable) 281 return; 282 283 /* 284 * If we haven't yet loaded the indirect vdevs' mappings, we 285 * can only read from blocks that we carefully ensure are on 286 * concrete vdevs (or previously-loaded indirect vdevs). So we 287 * can't allow the predictive prefetcher to attempt reads of other 288 * blocks (e.g. of the MOS's dnode obejct). 289 */ 290 if (!spa_indirect_vdevs_loaded(spa)) 291 return; 292 293 /* 294 * As a fast path for small (single-block) files, ignore access 295 * to the first block. 296 */ 297 if (!have_lock && blkid == 0) 298 return; 299 300 if (!have_lock) 301 rw_enter(&zf->zf_dnode->dn_struct_rwlock, RW_READER); 302 303 304 /* 305 * A fast path for small files for which no prefetch will 306 * happen. 307 */ 308 if (zf->zf_dnode->dn_maxblkid < 2) { 309 if (!have_lock) 310 rw_exit(&zf->zf_dnode->dn_struct_rwlock); 311 return; 312 } 313 rw_enter(&zf->zf_rwlock, RW_READER); 314 315 /* 316 * Find matching prefetch stream. Depending on whether the accesses 317 * are block-aligned, first block of the new access may either follow 318 * the last block of the previous access, or be equal to it. 319 */ 320 for (zs = list_head(&zf->zf_stream); zs != NULL; 321 zs = list_next(&zf->zf_stream, zs)) { 322 if (blkid == zs->zs_blkid || blkid + 1 == zs->zs_blkid) { 323 mutex_enter(&zs->zs_lock); 324 /* 325 * zs_blkid could have changed before we 326 * acquired zs_lock; re-check them here. 327 */ 328 if (blkid == zs->zs_blkid) { 329 break; 330 } else if (blkid + 1 == zs->zs_blkid) { 331 blkid++; 332 nblks--; 333 if (nblks == 0) { 334 /* Already prefetched this before. */ 335 mutex_exit(&zs->zs_lock); 336 rw_exit(&zf->zf_rwlock); 337 if (!have_lock) { 338 rw_exit(&zf->zf_dnode-> 339 dn_struct_rwlock); 340 } 341 return; 342 } 343 break; 344 } 345 mutex_exit(&zs->zs_lock); 346 } 347 } 348 349 if (zs == NULL) { 350 /* 351 * This access is not part of any existing stream. Create 352 * a new stream for it. 353 */ 354 ZFETCHSTAT_BUMP(zfetchstat_misses); 355 if (rw_tryupgrade(&zf->zf_rwlock)) 356 dmu_zfetch_stream_create(zf, end_of_access_blkid); 357 rw_exit(&zf->zf_rwlock); 358 if (!have_lock) 359 rw_exit(&zf->zf_dnode->dn_struct_rwlock); 360 return; 361 } 362 363 /* 364 * This access was to a block that we issued a prefetch for on 365 * behalf of this stream. Issue further prefetches for this stream. 366 * 367 * Normally, we start prefetching where we stopped 368 * prefetching last (zs_pf_blkid). But when we get our first 369 * hit on this stream, zs_pf_blkid == zs_blkid, we don't 370 * want to prefetch the block we just accessed. In this case, 371 * start just after the block we just accessed. 372 */ 373 pf_start = MAX(zs->zs_pf_blkid, end_of_access_blkid); 374 375 /* 376 * Double our amount of prefetched data, but don't let the 377 * prefetch get further ahead than zfetch_max_distance. 378 */ 379 if (fetch_data) { 380 max_dist_blks = 381 zfetch_max_distance >> zf->zf_dnode->dn_datablkshift; 382 /* 383 * Previously, we were (zs_pf_blkid - blkid) ahead. We 384 * want to now be double that, so read that amount again, 385 * plus the amount we are catching up by (i.e. the amount 386 * read just now). 387 */ 388 pf_ahead_blks = zs->zs_pf_blkid - blkid + nblks; 389 max_blks = max_dist_blks - (pf_start - end_of_access_blkid); 390 pf_nblks = MIN(pf_ahead_blks, max_blks); 391 } else { 392 pf_nblks = 0; 393 } 394 395 zs->zs_pf_blkid = pf_start + pf_nblks; 396 397 /* 398 * Do the same for indirects, starting from where we stopped last, 399 * or where we will stop reading data blocks (and the indirects 400 * that point to them). 401 */ 402 ipf_start = MAX(zs->zs_ipf_blkid, zs->zs_pf_blkid); 403 max_dist_blks = zfetch_max_idistance >> zf->zf_dnode->dn_datablkshift; 404 /* 405 * We want to double our distance ahead of the data prefetch 406 * (or reader, if we are not prefetching data). Previously, we 407 * were (zs_ipf_blkid - blkid) ahead. To double that, we read 408 * that amount again, plus the amount we are catching up by 409 * (i.e. the amount read now + the amount of data prefetched now). 410 */ 411 pf_ahead_blks = zs->zs_ipf_blkid - blkid + nblks + pf_nblks; 412 max_blks = max_dist_blks - (ipf_start - end_of_access_blkid); 413 ipf_nblks = MIN(pf_ahead_blks, max_blks); 414 zs->zs_ipf_blkid = ipf_start + ipf_nblks; 415 416 epbs = zf->zf_dnode->dn_indblkshift - SPA_BLKPTRSHIFT; 417 ipf_istart = P2ROUNDUP(ipf_start, 1 << epbs) >> epbs; 418 ipf_iend = P2ROUNDUP(zs->zs_ipf_blkid, 1 << epbs) >> epbs; 419 420 zs->zs_atime = gethrtime(); 421 /* no prior reads in progress */ 422 if (zfs_refcount_count(&zs->zs_blocks) == 0) 423 zs->zs_start_time = zs->zs_atime; 424 zs->zs_blkid = end_of_access_blkid; 425 zfs_refcount_add_few(&zs->zs_blocks, pf_nblks + ipf_iend - ipf_istart, 426 NULL); 427 mutex_exit(&zs->zs_lock); 428 rw_exit(&zf->zf_rwlock); 429 issued = 0; 430 431 /* 432 * dbuf_prefetch() is asynchronous (even when it needs to read 433 * indirect blocks), but we still prefer to drop our locks before 434 * calling it to reduce the time we hold them. 435 */ 436 437 for (int i = 0; i < pf_nblks; i++) { 438 issued += dbuf_prefetch_impl(zf->zf_dnode, 0, pf_start + i, 439 ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH, 440 dmu_zfetch_stream_done, zs); 441 } 442 for (int64_t iblk = ipf_istart; iblk < ipf_iend; iblk++) { 443 issued += dbuf_prefetch_impl(zf->zf_dnode, 1, iblk, 444 ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH, 445 dmu_zfetch_stream_done, zs); 446 } 447 if (!have_lock) 448 rw_exit(&zf->zf_dnode->dn_struct_rwlock); 449 ZFETCHSTAT_BUMP(zfetchstat_hits); 450 451 if (issued) 452 ZFETCHSTAT_ADD(zfetchstat_io_issued, issued); 453 } 454