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 /*
239 * Find matching prefetch stream. Depending on whether the accesses
240 * are block-aligned, first block of the new access may either follow
241 * the last block of the previous access, or be equal to it.
242 */
243 for (zs = list_head(&zf->zf_stream); zs != NULL;
244 zs = list_next(&zf->zf_stream, zs)) {
245 if (blkid == zs->zs_blkid || blkid + 1 == zs->zs_blkid) {
246 mutex_enter(&zs->zs_lock);
247 /*
248 * zs_blkid could have changed before we
249 * acquired zs_lock; re-check them here.
250 */
251 if (blkid == zs->zs_blkid) {
252 break;
253 } else if (blkid + 1 == zs->zs_blkid) {
254 blkid++;
255 nblks--;
256 if (nblks == 0) {
257 /* Already prefetched this before. */
258 mutex_exit(&zs->zs_lock);
259 rw_exit(&zf->zf_rwlock);
260 return;
261 }
262 break;
263 }
264 mutex_exit(&zs->zs_lock);
265 }
266 }
267
268 if (zs == NULL) {
269 /*
270 * This access is not part of any existing stream. Create
271 * a new stream for it.
272 */
273 ZFETCHSTAT_BUMP(zfetchstat_misses);
274 if (rw_tryupgrade(&zf->zf_rwlock))
275 dmu_zfetch_stream_create(zf, end_of_access_blkid);
276 rw_exit(&zf->zf_rwlock);
277 return;
278 }
279
280 /*
281 * This access was to a block that we issued a prefetch for on
282 * behalf of this stream. Issue further prefetches for this stream.
283 *
284 * Normally, we start prefetching where we stopped
285 * prefetching last (zs_pf_blkid). But when we get our first
286 * hit on this stream, zs_pf_blkid == zs_blkid, we don't
287 * want to prefetch the block we just accessed. In this case,
288 * start just after the block we just accessed.
289 */
290 pf_start = MAX(zs->zs_pf_blkid, end_of_access_blkid);
291
292 /*
293 * Double our amount of prefetched data, but don't let the
294 * prefetch get further ahead than zfetch_max_distance.
295 */
296 if (fetch_data) {
297 max_dist_blks =
298 zfetch_max_distance >> zf->zf_dnode->dn_datablkshift;
299 /*
300 * Previously, we were (zs_pf_blkid - blkid) ahead. We
301 * want to now be double that, so read that amount again,
302 * plus the amount we are catching up by (i.e. the amount
303 * read just now).
304 */
305 pf_ahead_blks = zs->zs_pf_blkid - blkid + nblks;
306 max_blks = max_dist_blks - (pf_start - end_of_access_blkid);
307 pf_nblks = MIN(pf_ahead_blks, max_blks);
308 } else {
309 pf_nblks = 0;
310 }
311
312 zs->zs_pf_blkid = pf_start + pf_nblks;
313
314 /*
315 * Do the same for indirects, starting from where we stopped last,
316 * or where we will stop reading data blocks (and the indirects
317 * that point to them).
318 */
319 ipf_start = MAX(zs->zs_ipf_blkid, zs->zs_pf_blkid);
320 max_dist_blks = zfetch_max_idistance >> zf->zf_dnode->dn_datablkshift;
321 /*
322 * We want to double our distance ahead of the data prefetch
323 * (or reader, if we are not prefetching data). Previously, we
324 * were (zs_ipf_blkid - blkid) ahead. To double that, we read
325 * that amount again, plus the amount we are catching up by
326 * (i.e. the amount read now + the amount of data prefetched now).
327 */
328 pf_ahead_blks = zs->zs_ipf_blkid - blkid + nblks + pf_nblks;
329 max_blks = max_dist_blks - (ipf_start - end_of_access_blkid);
330 ipf_nblks = MIN(pf_ahead_blks, max_blks);
331 zs->zs_ipf_blkid = ipf_start + ipf_nblks;
332
333 epbs = zf->zf_dnode->dn_indblkshift - SPA_BLKPTRSHIFT;
334 ipf_istart = P2ROUNDUP(ipf_start, 1 << epbs) >> epbs;
335 ipf_iend = P2ROUNDUP(zs->zs_ipf_blkid, 1 << epbs) >> epbs;
336
337 zs->zs_atime = gethrtime();
338 zs->zs_blkid = end_of_access_blkid;
339 mutex_exit(&zs->zs_lock);
340 rw_exit(&zf->zf_rwlock);
341
342 /*
343 * dbuf_prefetch() is asynchronous (even when it needs to read
344 * indirect blocks), but we still prefer to drop our locks before
345 * calling it to reduce the time we hold them.
346 */
347
348 for (int i = 0; i < pf_nblks; i++) {
349 dbuf_prefetch(zf->zf_dnode, 0, pf_start + i,
350 ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH);
351 }
352 for (int64_t iblk = ipf_istart; iblk < ipf_iend; iblk++) {
353 dbuf_prefetch(zf->zf_dnode, 1, iblk,
354 ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH);
355 }
356 ZFETCHSTAT_BUMP(zfetchstat_hits);
357 }