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 typedef struct zfetch_stats { 58 kstat_named_t zfetchstat_hits; 59 kstat_named_t zfetchstat_misses; 60 kstat_named_t zfetchstat_max_streams; 61 } zfetch_stats_t; 62 63 static zfetch_stats_t zfetch_stats = { 64 { "hits", KSTAT_DATA_UINT64 }, 65 { "misses", KSTAT_DATA_UINT64 }, 66 { "max_streams", KSTAT_DATA_UINT64 }, 67 }; 68 69 #define ZFETCHSTAT_BUMP(stat) \ 70 atomic_inc_64(&zfetch_stats.stat.value.ui64); 71 72 kstat_t *zfetch_ksp; 73 74 void 75 zfetch_init(void) 76 { 77 zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc", 78 KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t), 79 KSTAT_FLAG_VIRTUAL); 80 81 if (zfetch_ksp != NULL) { 82 zfetch_ksp->ks_data = &zfetch_stats; 83 kstat_install(zfetch_ksp); 84 } 85 } 86 87 void 88 zfetch_fini(void) 89 { 90 if (zfetch_ksp != NULL) { 91 kstat_delete(zfetch_ksp); 92 zfetch_ksp = NULL; 93 } 94 } 95 96 /* 97 * This takes a pointer to a zfetch structure and a dnode. It performs the 98 * necessary setup for the zfetch structure, grokking data from the 99 * associated dnode. 100 */ 101 void 102 dmu_zfetch_init(zfetch_t *zf, dnode_t *dno) 103 { 104 if (zf == NULL) 105 return; 106 107 zf->zf_dnode = dno; 108 109 list_create(&zf->zf_stream, sizeof (zstream_t), 110 offsetof(zstream_t, zs_node)); 111 112 rw_init(&zf->zf_rwlock, NULL, RW_DEFAULT, NULL); 113 } 114 115 static void 116 dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs) 117 { 118 ASSERT(RW_WRITE_HELD(&zf->zf_rwlock)); 119 list_remove(&zf->zf_stream, zs); 120 mutex_destroy(&zs->zs_lock); 121 kmem_free(zs, sizeof (*zs)); 122 } 123 124 /* 125 * Clean-up state associated with a zfetch structure (e.g. destroy the 126 * streams). This doesn't free the zfetch_t itself, that's left to the caller. 127 */ 128 void 129 dmu_zfetch_fini(zfetch_t *zf) 130 { 131 zstream_t *zs; 132 133 ASSERT(!RW_LOCK_HELD(&zf->zf_rwlock)); 134 135 rw_enter(&zf->zf_rwlock, RW_WRITER); 136 while ((zs = list_head(&zf->zf_stream)) != NULL) 137 dmu_zfetch_stream_remove(zf, zs); 138 rw_exit(&zf->zf_rwlock); 139 list_destroy(&zf->zf_stream); 140 rw_destroy(&zf->zf_rwlock); 141 142 zf->zf_dnode = NULL; 143 } 144 145 /* 146 * If there aren't too many streams already, create a new stream. 147 * The "blkid" argument is the next block that we expect this stream to access. 148 * While we're here, clean up old streams (which haven't been 149 * accessed for at least zfetch_min_sec_reap seconds). 150 */ 151 static void 152 dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid) 153 { 154 zstream_t *zs_next; 155 int numstreams = 0; 156 157 ASSERT(RW_WRITE_HELD(&zf->zf_rwlock)); 158 159 /* 160 * Clean up old streams. 161 */ 162 for (zstream_t *zs = list_head(&zf->zf_stream); 163 zs != NULL; zs = zs_next) { 164 zs_next = list_next(&zf->zf_stream, zs); 165 if (((gethrtime() - zs->zs_atime) / NANOSEC) > 166 zfetch_min_sec_reap) 167 dmu_zfetch_stream_remove(zf, zs); 168 else 169 numstreams++; 170 } 171 172 /* 173 * The maximum number of streams is normally zfetch_max_streams, 174 * but for small files we lower it such that it's at least possible 175 * for all the streams to be non-overlapping. 176 * 177 * If we are already at the maximum number of streams for this file, 178 * even after removing old streams, then don't create this stream. 179 */ 180 uint32_t max_streams = MAX(1, MIN(zfetch_max_streams, 181 zf->zf_dnode->dn_maxblkid * zf->zf_dnode->dn_datablksz / 182 zfetch_max_distance)); 183 if (numstreams >= max_streams) { 184 ZFETCHSTAT_BUMP(zfetchstat_max_streams); 185 return; 186 } 187 188 zstream_t *zs = kmem_zalloc(sizeof (*zs), KM_SLEEP); 189 zs->zs_blkid = blkid; 190 zs->zs_pf_blkid = blkid; 191 zs->zs_ipf_blkid = blkid; 192 zs->zs_atime = gethrtime(); 193 mutex_init(&zs->zs_lock, NULL, MUTEX_DEFAULT, NULL); 194 195 list_insert_head(&zf->zf_stream, zs); 196 } 197 198 /* 199 * This is the predictive prefetch entry point. It associates dnode access 200 * specified with blkid and nblks arguments with prefetch stream, predicts 201 * further accesses based on that stats and initiates speculative prefetch. 202 * fetch_data argument specifies whether actual data blocks should be fetched: 203 * FALSE -- prefetch only indirect blocks for predicted data blocks; 204 * TRUE -- prefetch predicted data blocks plus following indirect blocks. 205 */ 206 void 207 dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks, boolean_t fetch_data) 208 { 209 zstream_t *zs; 210 int64_t pf_start, ipf_start, ipf_istart, ipf_iend; 211 int64_t pf_ahead_blks, max_blks; 212 int epbs, max_dist_blks, pf_nblks, ipf_nblks; 213 uint64_t end_of_access_blkid = blkid + nblks; 214 spa_t *spa = zf->zf_dnode->dn_objset->os_spa; 215 216 if (zfs_prefetch_disable) 217 return; 218 219 /* 220 * If we haven't yet loaded the indirect vdevs' mappings, we 221 * can only read from blocks that we carefully ensure are on 222 * concrete vdevs (or previously-loaded indirect vdevs). So we 223 * can't allow the predictive prefetcher to attempt reads of other 224 * blocks (e.g. of the MOS's dnode obejct). 225 */ 226 if (!spa_indirect_vdevs_loaded(spa)) 227 return; 228 229 /* 230 * As a fast path for small (single-block) files, ignore access 231 * to the first block. 232 */ 233 if (blkid == 0) 234 return; 235 236 rw_enter(&zf->zf_rwlock, RW_READER); 237 238 for (zs = list_head(&zf->zf_stream); zs != NULL; 239 zs = list_next(&zf->zf_stream, zs)) { 240 if (blkid == zs->zs_blkid) { 241 mutex_enter(&zs->zs_lock); 242 /* 243 * zs_blkid could have changed before we 244 * acquired zs_lock; re-check them here. 245 */ 246 if (blkid != zs->zs_blkid) { 247 mutex_exit(&zs->zs_lock); 248 continue; 249 } 250 break; 251 } 252 } 253 254 if (zs == NULL) { 255 /* 256 * This access is not part of any existing stream. Create 257 * a new stream for it. 258 */ 259 ZFETCHSTAT_BUMP(zfetchstat_misses); 260 if (rw_tryupgrade(&zf->zf_rwlock)) 261 dmu_zfetch_stream_create(zf, end_of_access_blkid); 262 rw_exit(&zf->zf_rwlock); 263 return; 264 } 265 266 /* 267 * This access was to a block that we issued a prefetch for on 268 * behalf of this stream. Issue further prefetches for this stream. 269 * 270 * Normally, we start prefetching where we stopped 271 * prefetching last (zs_pf_blkid). But when we get our first 272 * hit on this stream, zs_pf_blkid == zs_blkid, we don't 273 * want to prefetch the block we just accessed. In this case, 274 * start just after the block we just accessed. 275 */ 276 pf_start = MAX(zs->zs_pf_blkid, end_of_access_blkid); 277 278 /* 279 * Double our amount of prefetched data, but don't let the 280 * prefetch get further ahead than zfetch_max_distance. 281 */ 282 if (fetch_data) { 283 max_dist_blks = 284 zfetch_max_distance >> zf->zf_dnode->dn_datablkshift; 285 /* 286 * Previously, we were (zs_pf_blkid - blkid) ahead. We 287 * want to now be double that, so read that amount again, 288 * plus the amount we are catching up by (i.e. the amount 289 * read just now). 290 */ 291 pf_ahead_blks = zs->zs_pf_blkid - blkid + nblks; 292 max_blks = max_dist_blks - (pf_start - end_of_access_blkid); 293 pf_nblks = MIN(pf_ahead_blks, max_blks); 294 } else { 295 pf_nblks = 0; 296 } 297 298 zs->zs_pf_blkid = pf_start + pf_nblks; 299 300 /* 301 * Do the same for indirects, starting from where we stopped last, 302 * or where we will stop reading data blocks (and the indirects 303 * that point to them). 304 */ 305 ipf_start = MAX(zs->zs_ipf_blkid, zs->zs_pf_blkid); 306 max_dist_blks = zfetch_max_idistance >> zf->zf_dnode->dn_datablkshift; 307 /* 308 * We want to double our distance ahead of the data prefetch 309 * (or reader, if we are not prefetching data). Previously, we 310 * were (zs_ipf_blkid - blkid) ahead. To double that, we read 311 * that amount again, plus the amount we are catching up by 312 * (i.e. the amount read now + the amount of data prefetched now). 313 */ 314 pf_ahead_blks = zs->zs_ipf_blkid - blkid + nblks + pf_nblks; 315 max_blks = max_dist_blks - (ipf_start - end_of_access_blkid); 316 ipf_nblks = MIN(pf_ahead_blks, max_blks); 317 zs->zs_ipf_blkid = ipf_start + ipf_nblks; 318 319 epbs = zf->zf_dnode->dn_indblkshift - SPA_BLKPTRSHIFT; 320 ipf_istart = P2ROUNDUP(ipf_start, 1 << epbs) >> epbs; 321 ipf_iend = P2ROUNDUP(zs->zs_ipf_blkid, 1 << epbs) >> epbs; 322 323 zs->zs_atime = gethrtime(); 324 zs->zs_blkid = end_of_access_blkid; 325 mutex_exit(&zs->zs_lock); 326 rw_exit(&zf->zf_rwlock); 327 328 /* 329 * dbuf_prefetch() is asynchronous (even when it needs to read 330 * indirect blocks), but we still prefer to drop our locks before 331 * calling it to reduce the time we hold them. 332 */ 333 334 for (int i = 0; i < pf_nblks; i++) { 335 dbuf_prefetch(zf->zf_dnode, 0, pf_start + i, 336 ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH); 337 } 338 for (int64_t iblk = ipf_istart; iblk < ipf_iend; iblk++) { 339 dbuf_prefetch(zf->zf_dnode, 1, iblk, 340 ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH); 341 } 342 ZFETCHSTAT_BUMP(zfetchstat_hits); 343 } 344