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 SYSCTL_DECL(_vfs_zfs_vdev);
93 SYSCTL_NODE(_vfs_zfs_vdev, OID_AUTO, cache, CTLFLAG_RW, 0, "ZFS VDEV Cache");
94 SYSCTL_INT(_vfs_zfs_vdev_cache, OID_AUTO, max, CTLFLAG_RDTUN,
95 &zfs_vdev_cache_max, 0, "Maximum I/O request size that increase read size");
96 SYSCTL_INT(_vfs_zfs_vdev_cache, OID_AUTO, size, CTLFLAG_RDTUN,
97 &zfs_vdev_cache_size, 0, "Size of VDEV cache");
98 SYSCTL_INT(_vfs_zfs_vdev_cache, OID_AUTO, bshift, CTLFLAG_RDTUN,
99 &zfs_vdev_cache_bshift, 0, "Turn too small requests into 1 << this value");
100
101 kstat_t *vdc_ksp = NULL;
102
103 typedef struct vdc_stats {
104 kstat_named_t vdc_stat_delegations;
105 kstat_named_t vdc_stat_hits;
106 kstat_named_t vdc_stat_misses;
107 } vdc_stats_t;
108
109 static vdc_stats_t vdc_stats = {
110 { "delegations", KSTAT_DATA_UINT64 },
111 { "hits", KSTAT_DATA_UINT64 },
112 { "misses", KSTAT_DATA_UINT64 }
113 };
114
115 #define VDCSTAT_BUMP(stat) atomic_inc_64(&vdc_stats.stat.value.ui64);
116
117 static inline int
vdev_cache_offset_compare(const void * a1,const void * a2)118 vdev_cache_offset_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 return (AVL_CMP(ve1->ve_offset, ve2->ve_offset));
124 }
125
126 static int
vdev_cache_lastused_compare(const void * a1,const void * a2)127 vdev_cache_lastused_compare(const void *a1, const void *a2)
128 {
129 const vdev_cache_entry_t *ve1 = (const vdev_cache_entry_t *)a1;
130 const vdev_cache_entry_t *ve2 = (const vdev_cache_entry_t *)a2;
131
132 int cmp = AVL_CMP(ve1->ve_lastused, ve2->ve_lastused);
133 if (likely(cmp))
134 return (cmp);
135
136 /*
137 * Among equally old entries, sort by offset to ensure uniqueness.
138 */
139 return (vdev_cache_offset_compare(a1, a2));
140 }
141
142 /*
143 * Evict the specified entry from the cache.
144 */
145 static void
vdev_cache_evict(vdev_cache_t * vc,vdev_cache_entry_t * ve)146 vdev_cache_evict(vdev_cache_t *vc, vdev_cache_entry_t *ve)
147 {
148 ASSERT(MUTEX_HELD(&vc->vc_lock));
149 ASSERT3P(ve->ve_fill_io, ==, NULL);
150 ASSERT3P(ve->ve_abd, !=, NULL);
151
152 avl_remove(&vc->vc_lastused_tree, ve);
153 avl_remove(&vc->vc_offset_tree, ve);
154 abd_free(ve->ve_abd);
155 kmem_free(ve, sizeof (vdev_cache_entry_t));
156 }
157
158 /*
159 * Allocate an entry in the cache. At the point we don't have the data,
160 * we're just creating a placeholder so that multiple threads don't all
161 * go off and read the same blocks.
162 */
163 static vdev_cache_entry_t *
vdev_cache_allocate(zio_t * zio)164 vdev_cache_allocate(zio_t *zio)
165 {
166 vdev_cache_t *vc = &zio->io_vd->vdev_cache;
167 uint64_t offset = P2ALIGN(zio->io_offset, VCBS);
168 vdev_cache_entry_t *ve;
169
170 ASSERT(MUTEX_HELD(&vc->vc_lock));
171
172 if (zfs_vdev_cache_size == 0)
173 return (NULL);
174
175 /*
176 * If adding a new entry would exceed the cache size,
177 * evict the oldest entry (LRU).
178 */
179 if ((avl_numnodes(&vc->vc_lastused_tree) << zfs_vdev_cache_bshift) >
180 zfs_vdev_cache_size) {
181 ve = avl_first(&vc->vc_lastused_tree);
182 if (ve->ve_fill_io != NULL)
183 return (NULL);
184 ASSERT3U(ve->ve_hits, !=, 0);
185 vdev_cache_evict(vc, ve);
186 }
187
188 ve = kmem_zalloc(sizeof (vdev_cache_entry_t), KM_SLEEP);
189 ve->ve_offset = offset;
190 ve->ve_lastused = ddi_get_lbolt();
191 ve->ve_abd = abd_alloc_for_io(VCBS, B_TRUE);
192
193 avl_add(&vc->vc_offset_tree, ve);
194 avl_add(&vc->vc_lastused_tree, ve);
195
196 return (ve);
197 }
198
199 static void
vdev_cache_hit(vdev_cache_t * vc,vdev_cache_entry_t * ve,zio_t * zio)200 vdev_cache_hit(vdev_cache_t *vc, vdev_cache_entry_t *ve, zio_t *zio)
201 {
202 uint64_t cache_phase = P2PHASE(zio->io_offset, VCBS);
203
204 ASSERT(MUTEX_HELD(&vc->vc_lock));
205 ASSERT3P(ve->ve_fill_io, ==, NULL);
206
207 if (ve->ve_lastused != ddi_get_lbolt()) {
208 avl_remove(&vc->vc_lastused_tree, ve);
209 ve->ve_lastused = ddi_get_lbolt();
210 avl_add(&vc->vc_lastused_tree, ve);
211 }
212
213 ve->ve_hits++;
214 abd_copy_off(zio->io_abd, ve->ve_abd, 0, cache_phase, zio->io_size);
215 }
216
217 /*
218 * Fill a previously allocated cache entry with data.
219 */
220 static void
vdev_cache_fill(zio_t * fio)221 vdev_cache_fill(zio_t *fio)
222 {
223 vdev_t *vd = fio->io_vd;
224 vdev_cache_t *vc = &vd->vdev_cache;
225 vdev_cache_entry_t *ve = fio->io_private;
226 zio_t *pio;
227
228 ASSERT3U(fio->io_size, ==, VCBS);
229
230 /*
231 * Add data to the cache.
232 */
233 mutex_enter(&vc->vc_lock);
234
235 ASSERT3P(ve->ve_fill_io, ==, fio);
236 ASSERT3U(ve->ve_offset, ==, fio->io_offset);
237 ASSERT3P(ve->ve_abd, ==, fio->io_abd);
238
239 ve->ve_fill_io = NULL;
240
241 /*
242 * Even if this cache line was invalidated by a missed write update,
243 * any reads that were queued up before the missed update are still
244 * valid, so we can satisfy them from this line before we evict it.
245 */
246 zio_link_t *zl = NULL;
247 while ((pio = zio_walk_parents(fio, &zl)) != NULL)
248 vdev_cache_hit(vc, ve, pio);
249
250 if (fio->io_error || ve->ve_missed_update)
251 vdev_cache_evict(vc, ve);
252
253 mutex_exit(&vc->vc_lock);
254 }
255
256 /*
257 * Read data from the cache. Returns B_TRUE cache hit, B_FALSE on miss.
258 */
259 boolean_t
vdev_cache_read(zio_t * zio)260 vdev_cache_read(zio_t *zio)
261 {
262 vdev_cache_t *vc = &zio->io_vd->vdev_cache;
263 vdev_cache_entry_t *ve, ve_search;
264 uint64_t cache_offset = P2ALIGN(zio->io_offset, VCBS);
265 uint64_t cache_phase = P2PHASE(zio->io_offset, VCBS);
266 zio_t *fio;
267
268 ASSERT3U(zio->io_type, ==, ZIO_TYPE_READ);
269
270 if (zio->io_flags & ZIO_FLAG_DONT_CACHE)
271 return (B_FALSE);
272
273 if (zio->io_size > zfs_vdev_cache_max)
274 return (B_FALSE);
275
276 /*
277 * If the I/O straddles two or more cache blocks, don't cache it.
278 */
279 if (P2BOUNDARY(zio->io_offset, zio->io_size, VCBS))
280 return (B_FALSE);
281
282 ASSERT3U(cache_phase + zio->io_size, <=, VCBS);
283
284 mutex_enter(&vc->vc_lock);
285
286 ve_search.ve_offset = cache_offset;
287 ve = avl_find(&vc->vc_offset_tree, &ve_search, NULL);
288
289 if (ve != NULL) {
290 if (ve->ve_missed_update) {
291 mutex_exit(&vc->vc_lock);
292 return (B_FALSE);
293 }
294
295 if ((fio = ve->ve_fill_io) != NULL) {
296 zio_vdev_io_bypass(zio);
297 zio_add_child(zio, fio);
298 mutex_exit(&vc->vc_lock);
299 VDCSTAT_BUMP(vdc_stat_delegations);
300 return (B_TRUE);
301 }
302
303 vdev_cache_hit(vc, ve, zio);
304 zio_vdev_io_bypass(zio);
305
306 mutex_exit(&vc->vc_lock);
307 VDCSTAT_BUMP(vdc_stat_hits);
308 return (B_TRUE);
309 }
310
311 ve = vdev_cache_allocate(zio);
312
313 if (ve == NULL) {
314 mutex_exit(&vc->vc_lock);
315 return (B_FALSE);
316 }
317
318 fio = zio_vdev_delegated_io(zio->io_vd, cache_offset,
319 ve->ve_abd, VCBS, ZIO_TYPE_READ, ZIO_PRIORITY_NOW,
320 ZIO_FLAG_DONT_CACHE, vdev_cache_fill, ve);
321
322 ve->ve_fill_io = fio;
323 zio_vdev_io_bypass(zio);
324 zio_add_child(zio, fio);
325
326 mutex_exit(&vc->vc_lock);
327 zio_nowait(fio);
328 VDCSTAT_BUMP(vdc_stat_misses);
329
330 return (B_TRUE);
331 }
332
333 /*
334 * Update cache contents upon write completion.
335 */
336 void
vdev_cache_write(zio_t * zio)337 vdev_cache_write(zio_t *zio)
338 {
339 vdev_cache_t *vc = &zio->io_vd->vdev_cache;
340 vdev_cache_entry_t *ve, ve_search;
341 uint64_t io_start = zio->io_offset;
342 uint64_t io_end = io_start + zio->io_size;
343 uint64_t min_offset = P2ALIGN(io_start, VCBS);
344 uint64_t max_offset = P2ROUNDUP(io_end, VCBS);
345 avl_index_t where;
346
347 ASSERT3U(zio->io_type, ==, ZIO_TYPE_WRITE);
348
349 mutex_enter(&vc->vc_lock);
350
351 ve_search.ve_offset = min_offset;
352 ve = avl_find(&vc->vc_offset_tree, &ve_search, &where);
353
354 if (ve == NULL)
355 ve = avl_nearest(&vc->vc_offset_tree, where, AVL_AFTER);
356
357 while (ve != NULL && ve->ve_offset < max_offset) {
358 uint64_t start = MAX(ve->ve_offset, io_start);
359 uint64_t end = MIN(ve->ve_offset + VCBS, io_end);
360
361 if (ve->ve_fill_io != NULL) {
362 ve->ve_missed_update = 1;
363 } else {
364 abd_copy_off(ve->ve_abd, zio->io_abd,
365 start - ve->ve_offset, start - io_start,
366 end - start);
367 }
368 ve = AVL_NEXT(&vc->vc_offset_tree, ve);
369 }
370 mutex_exit(&vc->vc_lock);
371 }
372
373 void
vdev_cache_purge(vdev_t * vd)374 vdev_cache_purge(vdev_t *vd)
375 {
376 vdev_cache_t *vc = &vd->vdev_cache;
377 vdev_cache_entry_t *ve;
378
379 mutex_enter(&vc->vc_lock);
380 while ((ve = avl_first(&vc->vc_offset_tree)) != NULL)
381 vdev_cache_evict(vc, ve);
382 mutex_exit(&vc->vc_lock);
383 }
384
385 void
vdev_cache_init(vdev_t * vd)386 vdev_cache_init(vdev_t *vd)
387 {
388 vdev_cache_t *vc = &vd->vdev_cache;
389
390 mutex_init(&vc->vc_lock, NULL, MUTEX_DEFAULT, NULL);
391
392 avl_create(&vc->vc_offset_tree, vdev_cache_offset_compare,
393 sizeof (vdev_cache_entry_t),
394 offsetof(struct vdev_cache_entry, ve_offset_node));
395
396 avl_create(&vc->vc_lastused_tree, vdev_cache_lastused_compare,
397 sizeof (vdev_cache_entry_t),
398 offsetof(struct vdev_cache_entry, ve_lastused_node));
399 }
400
401 void
vdev_cache_fini(vdev_t * vd)402 vdev_cache_fini(vdev_t *vd)
403 {
404 vdev_cache_t *vc = &vd->vdev_cache;
405
406 vdev_cache_purge(vd);
407
408 avl_destroy(&vc->vc_offset_tree);
409 avl_destroy(&vc->vc_lastused_tree);
410
411 mutex_destroy(&vc->vc_lock);
412 }
413
414 void
vdev_cache_stat_init(void)415 vdev_cache_stat_init(void)
416 {
417 vdc_ksp = kstat_create("zfs", 0, "vdev_cache_stats", "misc",
418 KSTAT_TYPE_NAMED, sizeof (vdc_stats) / sizeof (kstat_named_t),
419 KSTAT_FLAG_VIRTUAL);
420 if (vdc_ksp != NULL) {
421 vdc_ksp->ks_data = &vdc_stats;
422 kstat_install(vdc_ksp);
423 }
424 }
425
426 void
vdev_cache_stat_fini(void)427 vdev_cache_stat_fini(void)
428 {
429 if (vdc_ksp != NULL) {
430 kstat_delete(vdc_ksp);
431 vdc_ksp = NULL;
432 }
433 }
434