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, 2017 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 #include <sys/abd.h> 35 36 /* 37 * Virtual device read-ahead caching. 38 * 39 * This file implements a simple LRU read-ahead cache. When the DMU reads 40 * a given block, it will often want other, nearby blocks soon thereafter. 41 * We take advantage of this by reading a larger disk region and caching 42 * the result. In the best case, this can turn 128 back-to-back 512-byte 43 * reads into a single 64k read followed by 127 cache hits; this reduces 44 * latency dramatically. In the worst case, it can turn an isolated 512-byte 45 * read into a 64k read, which doesn't affect latency all that much but is 46 * terribly wasteful of bandwidth. A more intelligent version of the cache 47 * could keep track of access patterns and not do read-ahead unless it sees 48 * at least two temporally close I/Os to the same region. Currently, only 49 * metadata I/O is inflated. A futher enhancement could take advantage of 50 * more semantic information about the I/O. And it could use something 51 * faster than an AVL tree; that was chosen solely for convenience. 52 * 53 * There are five cache operations: allocate, fill, read, write, evict. 54 * 55 * (1) Allocate. This reserves a cache entry for the specified region. 56 * We separate the allocate and fill operations so that multiple threads 57 * don't generate I/O for the same cache miss. 58 * 59 * (2) Fill. When the I/O for a cache miss completes, the fill routine 60 * places the data in the previously allocated cache entry. 61 * 62 * (3) Read. Read data from the cache. 63 * 64 * (4) Write. Update cache contents after write completion. 65 * 66 * (5) Evict. When allocating a new entry, we evict the oldest (LRU) entry 67 * if the total cache size exceeds zfs_vdev_cache_size. 68 */ 69 70 /* 71 * These tunables are for performance analysis. 72 */ 73 /* 74 * All i/os smaller than zfs_vdev_cache_max will be turned into 75 * 1<<zfs_vdev_cache_bshift byte reads by the vdev_cache (aka software 76 * track buffer). At most zfs_vdev_cache_size bytes will be kept in each 77 * vdev's vdev_cache. 78 * 79 * TODO: Note that with the current ZFS code, it turns out that the 80 * vdev cache is not helpful, and in some cases actually harmful. It 81 * is better if we disable this. Once some time has passed, we should 82 * actually remove this to simplify the code. For now we just disable 83 * it by setting the zfs_vdev_cache_size to zero. Note that Solaris 11 84 * has made these same changes. 85 */ 86 int zfs_vdev_cache_max = 1<<14; /* 16KB */ 87 int zfs_vdev_cache_size = 0; 88 int zfs_vdev_cache_bshift = 16; 89 90 #define VCBS (1 << zfs_vdev_cache_bshift) /* 64KB */ 91 92 kstat_t *vdc_ksp = NULL; 93 94 typedef struct vdc_stats { 95 kstat_named_t vdc_stat_delegations; 96 kstat_named_t vdc_stat_hits; 97 kstat_named_t vdc_stat_misses; 98 } vdc_stats_t; 99 100 static vdc_stats_t vdc_stats = { 101 { "delegations", KSTAT_DATA_UINT64 }, 102 { "hits", KSTAT_DATA_UINT64 }, 103 { "misses", KSTAT_DATA_UINT64 } 104 }; 105 106 #define VDCSTAT_BUMP(stat) atomic_inc_64(&vdc_stats.stat.value.ui64); 107 108 static inline int 109 vdev_cache_offset_compare(const void *a1, const void *a2) 110 { 111 const vdev_cache_entry_t *ve1 = (const vdev_cache_entry_t *)a1; 112 const vdev_cache_entry_t *ve2 = (const vdev_cache_entry_t *)a2; 113 114 return (AVL_CMP(ve1->ve_offset, ve2->ve_offset)); 115 } 116 117 static int 118 vdev_cache_lastused_compare(const void *a1, const void *a2) 119 { 120 const vdev_cache_entry_t *ve1 = (const vdev_cache_entry_t *)a1; 121 const vdev_cache_entry_t *ve2 = (const vdev_cache_entry_t *)a2; 122 123 int cmp = AVL_CMP(ve1->ve_lastused, ve2->ve_lastused); 124 if (likely(cmp)) 125 return (cmp); 126 127 /* 128 * Among equally old entries, sort by offset to ensure uniqueness. 129 */ 130 return (vdev_cache_offset_compare(a1, a2)); 131 } 132 133 /* 134 * Evict the specified entry from the cache. 135 */ 136 static void 137 vdev_cache_evict(vdev_cache_t *vc, vdev_cache_entry_t *ve) 138 { 139 ASSERT(MUTEX_HELD(&vc->vc_lock)); 140 ASSERT3P(ve->ve_fill_io, ==, NULL); 141 ASSERT3P(ve->ve_abd, !=, NULL); 142 143 avl_remove(&vc->vc_lastused_tree, ve); 144 avl_remove(&vc->vc_offset_tree, ve); 145 abd_free(ve->ve_abd); 146 kmem_free(ve, sizeof (vdev_cache_entry_t)); 147 } 148 149 /* 150 * Allocate an entry in the cache. At the point we don't have the data, 151 * we're just creating a placeholder so that multiple threads don't all 152 * go off and read the same blocks. 153 */ 154 static vdev_cache_entry_t * 155 vdev_cache_allocate(zio_t *zio) 156 { 157 vdev_cache_t *vc = &zio->io_vd->vdev_cache; 158 uint64_t offset = P2ALIGN(zio->io_offset, VCBS); 159 vdev_cache_entry_t *ve; 160 161 ASSERT(MUTEX_HELD(&vc->vc_lock)); 162 163 if (zfs_vdev_cache_size == 0) 164 return (NULL); 165 166 /* 167 * If adding a new entry would exceed the cache size, 168 * evict the oldest entry (LRU). 169 */ 170 if ((avl_numnodes(&vc->vc_lastused_tree) << zfs_vdev_cache_bshift) > 171 zfs_vdev_cache_size) { 172 ve = avl_first(&vc->vc_lastused_tree); 173 if (ve->ve_fill_io != NULL) 174 return (NULL); 175 ASSERT3U(ve->ve_hits, !=, 0); 176 vdev_cache_evict(vc, ve); 177 } 178 179 ve = kmem_zalloc(sizeof (vdev_cache_entry_t), KM_SLEEP); 180 ve->ve_offset = offset; 181 ve->ve_lastused = ddi_get_lbolt(); 182 ve->ve_abd = abd_alloc_for_io(VCBS, B_TRUE); 183 184 avl_add(&vc->vc_offset_tree, ve); 185 avl_add(&vc->vc_lastused_tree, ve); 186 187 return (ve); 188 } 189 190 static void 191 vdev_cache_hit(vdev_cache_t *vc, vdev_cache_entry_t *ve, zio_t *zio) 192 { 193 uint64_t cache_phase = P2PHASE(zio->io_offset, VCBS); 194 195 ASSERT(MUTEX_HELD(&vc->vc_lock)); 196 ASSERT3P(ve->ve_fill_io, ==, NULL); 197 198 if (ve->ve_lastused != ddi_get_lbolt()) { 199 avl_remove(&vc->vc_lastused_tree, ve); 200 ve->ve_lastused = ddi_get_lbolt(); 201 avl_add(&vc->vc_lastused_tree, ve); 202 } 203 204 ve->ve_hits++; 205 abd_copy_off(zio->io_abd, ve->ve_abd, 0, cache_phase, zio->io_size); 206 } 207 208 /* 209 * Fill a previously allocated cache entry with data. 210 */ 211 static void 212 vdev_cache_fill(zio_t *fio) 213 { 214 vdev_t *vd = fio->io_vd; 215 vdev_cache_t *vc = &vd->vdev_cache; 216 vdev_cache_entry_t *ve = fio->io_private; 217 zio_t *pio; 218 219 ASSERT3U(fio->io_size, ==, VCBS); 220 221 /* 222 * Add data to the cache. 223 */ 224 mutex_enter(&vc->vc_lock); 225 226 ASSERT3P(ve->ve_fill_io, ==, fio); 227 ASSERT3U(ve->ve_offset, ==, fio->io_offset); 228 ASSERT3P(ve->ve_abd, ==, fio->io_abd); 229 230 ve->ve_fill_io = NULL; 231 232 /* 233 * Even if this cache line was invalidated by a missed write update, 234 * any reads that were queued up before the missed update are still 235 * valid, so we can satisfy them from this line before we evict it. 236 */ 237 zio_link_t *zl = NULL; 238 while ((pio = zio_walk_parents(fio, &zl)) != NULL) 239 vdev_cache_hit(vc, ve, pio); 240 241 if (fio->io_error || ve->ve_missed_update) 242 vdev_cache_evict(vc, ve); 243 244 mutex_exit(&vc->vc_lock); 245 } 246 247 /* 248 * Read data from the cache. Returns B_TRUE cache hit, B_FALSE on miss. 249 */ 250 boolean_t 251 vdev_cache_read(zio_t *zio) 252 { 253 vdev_cache_t *vc = &zio->io_vd->vdev_cache; 254 vdev_cache_entry_t *ve, ve_search; 255 uint64_t cache_offset = P2ALIGN(zio->io_offset, VCBS); 256 uint64_t cache_phase = P2PHASE(zio->io_offset, VCBS); 257 zio_t *fio; 258 259 ASSERT3U(zio->io_type, ==, ZIO_TYPE_READ); 260 261 if (zio->io_flags & ZIO_FLAG_DONT_CACHE) 262 return (B_FALSE); 263 264 if (zio->io_size > zfs_vdev_cache_max) 265 return (B_FALSE); 266 267 /* 268 * If the I/O straddles two or more cache blocks, don't cache it. 269 */ 270 if (P2BOUNDARY(zio->io_offset, zio->io_size, VCBS)) 271 return (B_FALSE); 272 273 ASSERT3U(cache_phase + zio->io_size, <=, VCBS); 274 275 mutex_enter(&vc->vc_lock); 276 277 ve_search.ve_offset = cache_offset; 278 ve = avl_find(&vc->vc_offset_tree, &ve_search, NULL); 279 280 if (ve != NULL) { 281 if (ve->ve_missed_update) { 282 mutex_exit(&vc->vc_lock); 283 return (B_FALSE); 284 } 285 286 if ((fio = ve->ve_fill_io) != NULL) { 287 zio_vdev_io_bypass(zio); 288 zio_add_child(zio, fio); 289 mutex_exit(&vc->vc_lock); 290 VDCSTAT_BUMP(vdc_stat_delegations); 291 return (B_TRUE); 292 } 293 294 vdev_cache_hit(vc, ve, zio); 295 zio_vdev_io_bypass(zio); 296 297 mutex_exit(&vc->vc_lock); 298 VDCSTAT_BUMP(vdc_stat_hits); 299 return (B_TRUE); 300 } 301 302 ve = vdev_cache_allocate(zio); 303 304 if (ve == NULL) { 305 mutex_exit(&vc->vc_lock); 306 return (B_FALSE); 307 } 308 309 fio = zio_vdev_delegated_io(zio->io_vd, cache_offset, 310 ve->ve_abd, VCBS, ZIO_TYPE_READ, ZIO_PRIORITY_NOW, 311 ZIO_FLAG_DONT_CACHE, vdev_cache_fill, ve); 312 313 ve->ve_fill_io = fio; 314 zio_vdev_io_bypass(zio); 315 zio_add_child(zio, fio); 316 317 mutex_exit(&vc->vc_lock); 318 zio_nowait(fio); 319 VDCSTAT_BUMP(vdc_stat_misses); 320 321 return (B_TRUE); 322 } 323 324 /* 325 * Update cache contents upon write completion. 326 */ 327 void 328 vdev_cache_write(zio_t *zio) 329 { 330 vdev_cache_t *vc = &zio->io_vd->vdev_cache; 331 vdev_cache_entry_t *ve, ve_search; 332 uint64_t io_start = zio->io_offset; 333 uint64_t io_end = io_start + zio->io_size; 334 uint64_t min_offset = P2ALIGN(io_start, VCBS); 335 uint64_t max_offset = P2ROUNDUP(io_end, VCBS); 336 avl_index_t where; 337 338 ASSERT3U(zio->io_type, ==, ZIO_TYPE_WRITE); 339 340 mutex_enter(&vc->vc_lock); 341 342 ve_search.ve_offset = min_offset; 343 ve = avl_find(&vc->vc_offset_tree, &ve_search, &where); 344 345 if (ve == NULL) 346 ve = avl_nearest(&vc->vc_offset_tree, where, AVL_AFTER); 347 348 while (ve != NULL && ve->ve_offset < max_offset) { 349 uint64_t start = MAX(ve->ve_offset, io_start); 350 uint64_t end = MIN(ve->ve_offset + VCBS, io_end); 351 352 if (ve->ve_fill_io != NULL) { 353 ve->ve_missed_update = 1; 354 } else { 355 abd_copy_off(ve->ve_abd, zio->io_abd, 356 start - ve->ve_offset, start - io_start, 357 end - start); 358 } 359 ve = AVL_NEXT(&vc->vc_offset_tree, ve); 360 } 361 mutex_exit(&vc->vc_lock); 362 } 363 364 void 365 vdev_cache_purge(vdev_t *vd) 366 { 367 vdev_cache_t *vc = &vd->vdev_cache; 368 vdev_cache_entry_t *ve; 369 370 mutex_enter(&vc->vc_lock); 371 while ((ve = avl_first(&vc->vc_offset_tree)) != NULL) 372 vdev_cache_evict(vc, ve); 373 mutex_exit(&vc->vc_lock); 374 } 375 376 void 377 vdev_cache_init(vdev_t *vd) 378 { 379 vdev_cache_t *vc = &vd->vdev_cache; 380 381 mutex_init(&vc->vc_lock, NULL, MUTEX_DEFAULT, NULL); 382 383 avl_create(&vc->vc_offset_tree, vdev_cache_offset_compare, 384 sizeof (vdev_cache_entry_t), 385 offsetof(struct vdev_cache_entry, ve_offset_node)); 386 387 avl_create(&vc->vc_lastused_tree, vdev_cache_lastused_compare, 388 sizeof (vdev_cache_entry_t), 389 offsetof(struct vdev_cache_entry, ve_lastused_node)); 390 } 391 392 void 393 vdev_cache_fini(vdev_t *vd) 394 { 395 vdev_cache_t *vc = &vd->vdev_cache; 396 397 vdev_cache_purge(vd); 398 399 avl_destroy(&vc->vc_offset_tree); 400 avl_destroy(&vc->vc_lastused_tree); 401 402 mutex_destroy(&vc->vc_lock); 403 } 404 405 void 406 vdev_cache_stat_init(void) 407 { 408 vdc_ksp = kstat_create("zfs", 0, "vdev_cache_stats", "misc", 409 KSTAT_TYPE_NAMED, sizeof (vdc_stats) / sizeof (kstat_named_t), 410 KSTAT_FLAG_VIRTUAL); 411 if (vdc_ksp != NULL) { 412 vdc_ksp->ks_data = &vdc_stats; 413 kstat_install(vdc_ksp); 414 } 415 } 416 417 void 418 vdev_cache_stat_fini(void) 419 { 420 if (vdc_ksp != NULL) { 421 kstat_delete(vdc_ksp); 422 vdc_ksp = NULL; 423 } 424 } 425