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, 2016 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 further 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 */ 86int zfs_vdev_cache_max = 1<<14; /* 16KB */ 87int zfs_vdev_cache_size = 0; 88int zfs_vdev_cache_bshift = 16; 89 90#define VCBS (1 << zfs_vdev_cache_bshift) /* 64KB */ 91 92kstat_t *vdc_ksp = NULL; 93 94typedef 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 100static 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 108static inline int 109vdev_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 (TREE_CMP(ve1->ve_offset, ve2->ve_offset)); 115} 116 117static int 118vdev_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 = TREE_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 */ 136static void 137vdev_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 */ 154static vdev_cache_entry_t * 155vdev_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 190static void 191vdev_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 */ 211static void 212vdev_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 */ 250boolean_t 251vdev_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 zio_t *fio; 257 uint64_t cache_phase __maybe_unused = P2PHASE(zio->io_offset, VCBS); 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 = kmem_alloc(sizeof (vdev_cache_entry_t), KM_SLEEP); 278 ve_search->ve_offset = cache_offset; 279 ve = avl_find(&vc->vc_offset_tree, ve_search, NULL); 280 kmem_free(ve_search, sizeof (vdev_cache_entry_t)); 281 282 if (ve != NULL) { 283 if (ve->ve_missed_update) { 284 mutex_exit(&vc->vc_lock); 285 return (B_FALSE); 286 } 287 288 if ((fio = ve->ve_fill_io) != NULL) { 289 zio_vdev_io_bypass(zio); 290 zio_add_child(zio, fio); 291 mutex_exit(&vc->vc_lock); 292 VDCSTAT_BUMP(vdc_stat_delegations); 293 return (B_TRUE); 294 } 295 296 vdev_cache_hit(vc, ve, zio); 297 zio_vdev_io_bypass(zio); 298 299 mutex_exit(&vc->vc_lock); 300 VDCSTAT_BUMP(vdc_stat_hits); 301 return (B_TRUE); 302 } 303 304 ve = vdev_cache_allocate(zio); 305 306 if (ve == NULL) { 307 mutex_exit(&vc->vc_lock); 308 return (B_FALSE); 309 } 310 311 fio = zio_vdev_delegated_io(zio->io_vd, cache_offset, 312 ve->ve_abd, VCBS, ZIO_TYPE_READ, ZIO_PRIORITY_NOW, 313 ZIO_FLAG_DONT_CACHE, vdev_cache_fill, ve); 314 315 ve->ve_fill_io = fio; 316 zio_vdev_io_bypass(zio); 317 zio_add_child(zio, fio); 318 319 mutex_exit(&vc->vc_lock); 320 zio_nowait(fio); 321 VDCSTAT_BUMP(vdc_stat_misses); 322 323 return (B_TRUE); 324} 325 326/* 327 * Update cache contents upon write completion. 328 */ 329void 330vdev_cache_write(zio_t *zio) 331{ 332 vdev_cache_t *vc = &zio->io_vd->vdev_cache; 333 vdev_cache_entry_t *ve, ve_search; 334 uint64_t io_start = zio->io_offset; 335 uint64_t io_end = io_start + zio->io_size; 336 uint64_t min_offset = P2ALIGN(io_start, VCBS); 337 uint64_t max_offset = P2ROUNDUP(io_end, VCBS); 338 avl_index_t where; 339 340 ASSERT3U(zio->io_type, ==, ZIO_TYPE_WRITE); 341 342 mutex_enter(&vc->vc_lock); 343 344 ve_search.ve_offset = min_offset; 345 ve = avl_find(&vc->vc_offset_tree, &ve_search, &where); 346 347 if (ve == NULL) 348 ve = avl_nearest(&vc->vc_offset_tree, where, AVL_AFTER); 349 350 while (ve != NULL && ve->ve_offset < max_offset) { 351 uint64_t start = MAX(ve->ve_offset, io_start); 352 uint64_t end = MIN(ve->ve_offset + VCBS, io_end); 353 354 if (ve->ve_fill_io != NULL) { 355 ve->ve_missed_update = 1; 356 } else { 357 abd_copy_off(ve->ve_abd, zio->io_abd, 358 start - ve->ve_offset, start - io_start, 359 end - start); 360 } 361 ve = AVL_NEXT(&vc->vc_offset_tree, ve); 362 } 363 mutex_exit(&vc->vc_lock); 364} 365 366void 367vdev_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 378void 379vdev_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 394void 395vdev_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 407void 408vdev_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 419void 420vdev_cache_stat_fini(void) 421{ 422 if (vdc_ksp != NULL) { 423 kstat_delete(vdc_ksp); 424 vdc_ksp = NULL; 425 } 426} 427 428/* BEGIN CSTYLED */ 429ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, cache_max, INT, ZMOD_RW, 430 "Inflate reads small than max"); 431 432ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, cache_size, INT, ZMOD_RD, 433 "Total size of the per-disk cache"); 434 435ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, cache_bshift, INT, ZMOD_RW, 436 "Shift size to inflate reads too"); 437/* END CSTYLED */ 438