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 * Copyright (c) 2013 by Delphix. All rights reserved. 27 */ 28 29 #include <sys/zfs_context.h> 30 #include <sys/spa.h> 31 #include <sys/vdev_impl.h> 32 #include <sys/zio.h> 33 #include <sys/kstat.h> 34 35 /* 36 * Virtual device read-ahead caching. 37 * 38 * This file implements a simple LRU read-ahead cache. When the DMU reads 39 * a given block, it will often want other, nearby blocks soon thereafter. 40 * We take advantage of this by reading a larger disk region and caching 41 * the result. In the best case, this can turn 128 back-to-back 512-byte 42 * reads into a single 64k read followed by 127 cache hits; this reduces 43 * latency dramatically. In the worst case, it can turn an isolated 512-byte 44 * read into a 64k read, which doesn't affect latency all that much but is 45 * terribly wasteful of bandwidth. A more intelligent version of the cache 46 * could keep track of access patterns and not do read-ahead unless it sees 47 * at least two temporally close I/Os to the same region. Currently, only 48 * metadata I/O is inflated. A futher enhancement could take advantage of 49 * more semantic information about the I/O. And it could use something 50 * faster than an AVL tree; that was chosen solely for convenience. 51 * 52 * There are five cache operations: allocate, fill, read, write, evict. 53 * 54 * (1) Allocate. This reserves a cache entry for the specified region. 55 * We separate the allocate and fill operations so that multiple threads 56 * don't generate I/O for the same cache miss. 57 * 58 * (2) Fill. When the I/O for a cache miss completes, the fill routine 59 * places the data in the previously allocated cache entry. 60 * 61 * (3) Read. Read data from the cache. 62 * 63 * (4) Write. Update cache contents after write completion. 64 * 65 * (5) Evict. When allocating a new entry, we evict the oldest (LRU) entry 66 * if the total cache size exceeds zfs_vdev_cache_size. 67 */ 68 69 /* 70 * These tunables are for performance analysis. 71 */ 72 /* 73 * All i/os smaller than zfs_vdev_cache_max will be turned into 74 * 1<<zfs_vdev_cache_bshift byte reads by the vdev_cache (aka software 75 * track buffer). At most zfs_vdev_cache_size bytes will be kept in each 76 * vdev's vdev_cache. 77 * 78 * TODO: Note that with the current ZFS code, it turns out that the 79 * vdev cache is not helpful, and in some cases actually harmful. It 80 * is better if we disable this. Once some time has passed, we should 81 * actually remove this to simplify the code. For now we just disable 82 * it by setting the zfs_vdev_cache_size to zero. Note that Solaris 11 83 * has made these same changes. 84 */ 85 int zfs_vdev_cache_max = 1<<14; /* 16KB */ 86 int zfs_vdev_cache_size = 0; 87 int zfs_vdev_cache_bshift = 16; 88 89 #define VCBS (1 << zfs_vdev_cache_bshift) /* 64KB */ 90 91 kstat_t *vdc_ksp = NULL; 92 93 typedef struct vdc_stats { 94 kstat_named_t vdc_stat_delegations; 95 kstat_named_t vdc_stat_hits; 96 kstat_named_t vdc_stat_misses; 97 } vdc_stats_t; 98 99 static vdc_stats_t vdc_stats = { 100 { "delegations", KSTAT_DATA_UINT64 }, 101 { "hits", KSTAT_DATA_UINT64 }, 102 { "misses", KSTAT_DATA_UINT64 } 103 }; 104 105 #define VDCSTAT_BUMP(stat) atomic_add_64(&vdc_stats.stat.value.ui64, 1); 106 107 static int 108 vdev_cache_offset_compare(const void *a1, const void *a2) 109 { 110 const vdev_cache_entry_t *ve1 = a1; 111 const vdev_cache_entry_t *ve2 = a2; 112 113 if (ve1->ve_offset < ve2->ve_offset) 114 return (-1); 115 if (ve1->ve_offset > ve2->ve_offset) 116 return (1); 117 return (0); 118 } 119 120 static int 121 vdev_cache_lastused_compare(const void *a1, const void *a2) 122 { 123 const vdev_cache_entry_t *ve1 = a1; 124 const vdev_cache_entry_t *ve2 = a2; 125 126 if (ve1->ve_lastused < ve2->ve_lastused) 127 return (-1); 128 if (ve1->ve_lastused > ve2->ve_lastused) 129 return (1); 130 131 /* 132 * Among equally old entries, sort by offset to ensure uniqueness. 133 */ 134 return (vdev_cache_offset_compare(a1, a2)); 135 } 136 137 /* 138 * Evict the specified entry from the cache. 139 */ 140 static void 141 vdev_cache_evict(vdev_cache_t *vc, vdev_cache_entry_t *ve) 142 { 143 ASSERT(MUTEX_HELD(&vc->vc_lock)); 144 ASSERT(ve->ve_fill_io == NULL); 145 ASSERT(ve->ve_data != NULL); 146 147 avl_remove(&vc->vc_lastused_tree, ve); 148 avl_remove(&vc->vc_offset_tree, ve); 149 zio_buf_free(ve->ve_data, VCBS); 150 kmem_free(ve, sizeof (vdev_cache_entry_t)); 151 } 152 153 /* 154 * Allocate an entry in the cache. At the point we don't have the data, 155 * we're just creating a placeholder so that multiple threads don't all 156 * go off and read the same blocks. 157 */ 158 static vdev_cache_entry_t * 159 vdev_cache_allocate(zio_t *zio) 160 { 161 vdev_cache_t *vc = &zio->io_vd->vdev_cache; 162 uint64_t offset = P2ALIGN(zio->io_offset, VCBS); 163 vdev_cache_entry_t *ve; 164 165 ASSERT(MUTEX_HELD(&vc->vc_lock)); 166 167 if (zfs_vdev_cache_size == 0) 168 return (NULL); 169 170 /* 171 * If adding a new entry would exceed the cache size, 172 * evict the oldest entry (LRU). 173 */ 174 if ((avl_numnodes(&vc->vc_lastused_tree) << zfs_vdev_cache_bshift) > 175 zfs_vdev_cache_size) { 176 ve = avl_first(&vc->vc_lastused_tree); 177 if (ve->ve_fill_io != NULL) 178 return (NULL); 179 ASSERT(ve->ve_hits != 0); 180 vdev_cache_evict(vc, ve); 181 } 182 183 ve = kmem_zalloc(sizeof (vdev_cache_entry_t), KM_SLEEP); 184 ve->ve_offset = offset; 185 ve->ve_lastused = ddi_get_lbolt(); 186 ve->ve_data = zio_buf_alloc(VCBS); 187 188 avl_add(&vc->vc_offset_tree, ve); 189 avl_add(&vc->vc_lastused_tree, ve); 190 191 return (ve); 192 } 193 194 static void 195 vdev_cache_hit(vdev_cache_t *vc, vdev_cache_entry_t *ve, zio_t *zio) 196 { 197 uint64_t cache_phase = P2PHASE(zio->io_offset, VCBS); 198 199 ASSERT(MUTEX_HELD(&vc->vc_lock)); 200 ASSERT(ve->ve_fill_io == NULL); 201 202 if (ve->ve_lastused != ddi_get_lbolt()) { 203 avl_remove(&vc->vc_lastused_tree, ve); 204 ve->ve_lastused = ddi_get_lbolt(); 205 avl_add(&vc->vc_lastused_tree, ve); 206 } 207 208 ve->ve_hits++; 209 bcopy(ve->ve_data + cache_phase, zio->io_data, zio->io_size); 210 } 211 212 /* 213 * Fill a previously allocated cache entry with data. 214 */ 215 static void 216 vdev_cache_fill(zio_t *fio) 217 { 218 vdev_t *vd = fio->io_vd; 219 vdev_cache_t *vc = &vd->vdev_cache; 220 vdev_cache_entry_t *ve = fio->io_private; 221 zio_t *pio; 222 223 ASSERT(fio->io_size == VCBS); 224 225 /* 226 * Add data to the cache. 227 */ 228 mutex_enter(&vc->vc_lock); 229 230 ASSERT(ve->ve_fill_io == fio); 231 ASSERT(ve->ve_offset == fio->io_offset); 232 ASSERT(ve->ve_data == fio->io_data); 233 234 ve->ve_fill_io = NULL; 235 236 /* 237 * Even if this cache line was invalidated by a missed write update, 238 * any reads that were queued up before the missed update are still 239 * valid, so we can satisfy them from this line before we evict it. 240 */ 241 while ((pio = zio_walk_parents(fio)) != NULL) 242 vdev_cache_hit(vc, ve, pio); 243 244 if (fio->io_error || ve->ve_missed_update) 245 vdev_cache_evict(vc, ve); 246 247 mutex_exit(&vc->vc_lock); 248 } 249 250 /* 251 * Read data from the cache. Returns B_TRUE cache hit, B_FALSE on miss. 252 */ 253 boolean_t 254 vdev_cache_read(zio_t *zio) 255 { 256 vdev_cache_t *vc = &zio->io_vd->vdev_cache; 257 vdev_cache_entry_t *ve, ve_search; 258 uint64_t cache_offset = P2ALIGN(zio->io_offset, VCBS); 259 uint64_t cache_phase = P2PHASE(zio->io_offset, VCBS); 260 zio_t *fio; 261 262 ASSERT(zio->io_type == ZIO_TYPE_READ); 263 264 if (zio->io_flags & ZIO_FLAG_DONT_CACHE) 265 return (B_FALSE); 266 267 if (zio->io_size > zfs_vdev_cache_max) 268 return (B_FALSE); 269 270 /* 271 * If the I/O straddles two or more cache blocks, don't cache it. 272 */ 273 if (P2BOUNDARY(zio->io_offset, zio->io_size, VCBS)) 274 return (B_FALSE); 275 276 ASSERT(cache_phase + zio->io_size <= VCBS); 277 278 mutex_enter(&vc->vc_lock); 279 280 ve_search.ve_offset = cache_offset; 281 ve = avl_find(&vc->vc_offset_tree, &ve_search, NULL); 282 283 if (ve != NULL) { 284 if (ve->ve_missed_update) { 285 mutex_exit(&vc->vc_lock); 286 return (B_FALSE); 287 } 288 289 if ((fio = ve->ve_fill_io) != NULL) { 290 zio_vdev_io_bypass(zio); 291 zio_add_child(zio, fio); 292 mutex_exit(&vc->vc_lock); 293 VDCSTAT_BUMP(vdc_stat_delegations); 294 return (B_TRUE); 295 } 296 297 vdev_cache_hit(vc, ve, zio); 298 zio_vdev_io_bypass(zio); 299 300 mutex_exit(&vc->vc_lock); 301 VDCSTAT_BUMP(vdc_stat_hits); 302 return (B_TRUE); 303 } 304 305 ve = vdev_cache_allocate(zio); 306 307 if (ve == NULL) { 308 mutex_exit(&vc->vc_lock); 309 return (B_FALSE); 310 } 311 312 fio = zio_vdev_delegated_io(zio->io_vd, cache_offset, 313 ve->ve_data, VCBS, ZIO_TYPE_READ, ZIO_PRIORITY_NOW, 314 ZIO_FLAG_DONT_CACHE, vdev_cache_fill, ve); 315 316 ve->ve_fill_io = fio; 317 zio_vdev_io_bypass(zio); 318 zio_add_child(zio, fio); 319 320 mutex_exit(&vc->vc_lock); 321 zio_nowait(fio); 322 VDCSTAT_BUMP(vdc_stat_misses); 323 324 return (B_TRUE); 325 } 326 327 /* 328 * Update cache contents upon write completion. 329 */ 330 void 331 vdev_cache_write(zio_t *zio) 332 { 333 vdev_cache_t *vc = &zio->io_vd->vdev_cache; 334 vdev_cache_entry_t *ve, ve_search; 335 uint64_t io_start = zio->io_offset; 336 uint64_t io_end = io_start + zio->io_size; 337 uint64_t min_offset = P2ALIGN(io_start, VCBS); 338 uint64_t max_offset = P2ROUNDUP(io_end, VCBS); 339 avl_index_t where; 340 341 ASSERT(zio->io_type == ZIO_TYPE_WRITE); 342 343 mutex_enter(&vc->vc_lock); 344 345 ve_search.ve_offset = min_offset; 346 ve = avl_find(&vc->vc_offset_tree, &ve_search, &where); 347 348 if (ve == NULL) 349 ve = avl_nearest(&vc->vc_offset_tree, where, AVL_AFTER); 350 351 while (ve != NULL && ve->ve_offset < max_offset) { 352 uint64_t start = MAX(ve->ve_offset, io_start); 353 uint64_t end = MIN(ve->ve_offset + VCBS, io_end); 354 355 if (ve->ve_fill_io != NULL) { 356 ve->ve_missed_update = 1; 357 } else { 358 bcopy((char *)zio->io_data + start - io_start, 359 ve->ve_data + start - ve->ve_offset, end - start); 360 } 361 ve = AVL_NEXT(&vc->vc_offset_tree, ve); 362 } 363 mutex_exit(&vc->vc_lock); 364 } 365 366 void 367 vdev_cache_purge(vdev_t *vd) 368 { 369 vdev_cache_t *vc = &vd->vdev_cache; 370 vdev_cache_entry_t *ve; 371 372 mutex_enter(&vc->vc_lock); 373 while ((ve = avl_first(&vc->vc_offset_tree)) != NULL) 374 vdev_cache_evict(vc, ve); 375 mutex_exit(&vc->vc_lock); 376 } 377 378 void 379 vdev_cache_init(vdev_t *vd) 380 { 381 vdev_cache_t *vc = &vd->vdev_cache; 382 383 mutex_init(&vc->vc_lock, NULL, MUTEX_DEFAULT, NULL); 384 385 avl_create(&vc->vc_offset_tree, vdev_cache_offset_compare, 386 sizeof (vdev_cache_entry_t), 387 offsetof(struct vdev_cache_entry, ve_offset_node)); 388 389 avl_create(&vc->vc_lastused_tree, vdev_cache_lastused_compare, 390 sizeof (vdev_cache_entry_t), 391 offsetof(struct vdev_cache_entry, ve_lastused_node)); 392 } 393 394 void 395 vdev_cache_fini(vdev_t *vd) 396 { 397 vdev_cache_t *vc = &vd->vdev_cache; 398 399 vdev_cache_purge(vd); 400 401 avl_destroy(&vc->vc_offset_tree); 402 avl_destroy(&vc->vc_lastused_tree); 403 404 mutex_destroy(&vc->vc_lock); 405 } 406 407 void 408 vdev_cache_stat_init(void) 409 { 410 vdc_ksp = kstat_create("zfs", 0, "vdev_cache_stats", "misc", 411 KSTAT_TYPE_NAMED, sizeof (vdc_stats) / sizeof (kstat_named_t), 412 KSTAT_FLAG_VIRTUAL); 413 if (vdc_ksp != NULL) { 414 vdc_ksp->ks_data = &vdc_stats; 415 kstat_install(vdc_ksp); 416 } 417 } 418 419 void 420 vdev_cache_stat_fini(void) 421 { 422 if (vdc_ksp != NULL) { 423 kstat_delete(vdc_ksp); 424 vdc_ksp = NULL; 425 } 426 } 427