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, 2017 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 kstat_named_t zfetchstat_max_completion_us;
62 kstat_named_t zfetchstat_last_completion_us;
63 kstat_named_t zfetchstat_io_issued;
64 } zfetch_stats_t;
65
66 static zfetch_stats_t zfetch_stats = {
67 { "hits", KSTAT_DATA_UINT64 },
68 { "misses", KSTAT_DATA_UINT64 },
69 { "max_streams", KSTAT_DATA_UINT64 },
70 { "max_completion_us", KSTAT_DATA_UINT64 },
71 { "last_completion_us", KSTAT_DATA_UINT64 },
72 { "io_issued", KSTAT_DATA_UINT64 },
73 };
74
75 #define ZFETCHSTAT_BUMP(stat) \
76 atomic_inc_64(&zfetch_stats.stat.value.ui64)
77 #define ZFETCHSTAT_ADD(stat, val) \
78 atomic_add_64(&zfetch_stats.stat.value.ui64, val)
79 #define ZFETCHSTAT_SET(stat, val) \
80 zfetch_stats.stat.value.ui64 = val
81 #define ZFETCHSTAT_GET(stat) \
82 zfetch_stats.stat.value.ui64
83
84
85 kstat_t *zfetch_ksp;
86
87 void
zfetch_init(void)88 zfetch_init(void)
89 {
90 zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc",
91 KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t),
92 KSTAT_FLAG_VIRTUAL);
93
94 if (zfetch_ksp != NULL) {
95 zfetch_ksp->ks_data = &zfetch_stats;
96 kstat_install(zfetch_ksp);
97 }
98 }
99
100 void
zfetch_fini(void)101 zfetch_fini(void)
102 {
103 if (zfetch_ksp != NULL) {
104 kstat_delete(zfetch_ksp);
105 zfetch_ksp = NULL;
106 }
107 }
108
109 /*
110 * This takes a pointer to a zfetch structure and a dnode. It performs the
111 * necessary setup for the zfetch structure, grokking data from the
112 * associated dnode.
113 */
114 void
dmu_zfetch_init(zfetch_t * zf,dnode_t * dno)115 dmu_zfetch_init(zfetch_t *zf, dnode_t *dno)
116 {
117 if (zf == NULL)
118 return;
119 zf->zf_dnode = dno;
120 zf->zf_numstreams = 0;
121
122 list_create(&zf->zf_stream, sizeof (zstream_t),
123 offsetof(zstream_t, zs_node));
124
125 rw_init(&zf->zf_rwlock, NULL, RW_DEFAULT, NULL);
126 }
127
128 static void
dmu_zfetch_stream_fini(zstream_t * zs)129 dmu_zfetch_stream_fini(zstream_t *zs)
130 {
131 mutex_destroy(&zs->zs_lock);
132 zfs_refcount_destroy(&zs->zs_blocks);
133 kmem_free(zs, sizeof (*zs));
134 }
135
136 static void
dmu_zfetch_stream_remove(zfetch_t * zf,zstream_t * zs)137 dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs)
138 {
139 ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
140 list_remove(&zf->zf_stream, zs);
141 dmu_zfetch_stream_fini(zs);
142 zf->zf_numstreams--;
143 }
144
145 static void
dmu_zfetch_stream_orphan(zfetch_t * zf,zstream_t * zs)146 dmu_zfetch_stream_orphan(zfetch_t *zf, zstream_t *zs)
147 {
148 ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
149 list_remove(&zf->zf_stream, zs);
150 zs->zs_fetch = NULL;
151 zf->zf_numstreams--;
152 }
153
154 /*
155 * Clean-up state associated with a zfetch structure (e.g. destroy the
156 * streams). This doesn't free the zfetch_t itself, that's left to the caller.
157 */
158 void
dmu_zfetch_fini(zfetch_t * zf)159 dmu_zfetch_fini(zfetch_t *zf)
160 {
161 zstream_t *zs;
162
163 ASSERT(!RW_LOCK_HELD(&zf->zf_rwlock));
164
165 rw_enter(&zf->zf_rwlock, RW_WRITER);
166 while ((zs = list_head(&zf->zf_stream)) != NULL) {
167 if (zfs_refcount_count(&zs->zs_blocks) != 0)
168 dmu_zfetch_stream_orphan(zf, zs);
169 else
170 dmu_zfetch_stream_remove(zf, zs);
171 }
172 rw_exit(&zf->zf_rwlock);
173 list_destroy(&zf->zf_stream);
174 rw_destroy(&zf->zf_rwlock);
175
176 zf->zf_dnode = NULL;
177 }
178
179 /*
180 * If there aren't too many streams already, create a new stream.
181 * The "blkid" argument is the next block that we expect this stream to access.
182 * While we're here, clean up old streams (which haven't been
183 * accessed for at least zfetch_min_sec_reap seconds).
184 */
185 static void
dmu_zfetch_stream_create(zfetch_t * zf,uint64_t blkid)186 dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid)
187 {
188 zstream_t *zs_next;
189 hrtime_t now = gethrtime();
190
191 ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
192
193 /*
194 * Clean up old streams.
195 */
196 for (zstream_t *zs = list_head(&zf->zf_stream);
197 zs != NULL; zs = zs_next) {
198 zs_next = list_next(&zf->zf_stream, zs);
199 /*
200 * Skip gethrtime() call if there are still references
201 */
202 if (zfs_refcount_count(&zs->zs_blocks) != 0)
203 continue;
204 if (((now - zs->zs_atime) / NANOSEC) >
205 zfetch_min_sec_reap)
206 dmu_zfetch_stream_remove(zf, zs);
207 }
208
209 /*
210 * The maximum number of streams is normally zfetch_max_streams,
211 * but for small files we lower it such that it's at least possible
212 * for all the streams to be non-overlapping.
213 *
214 * If we are already at the maximum number of streams for this file,
215 * even after removing old streams, then don't create this stream.
216 */
217 uint32_t max_streams = MAX(1, MIN(zfetch_max_streams,
218 zf->zf_dnode->dn_maxblkid * zf->zf_dnode->dn_datablksz /
219 zfetch_max_distance));
220 if (zf->zf_numstreams >= max_streams) {
221 ZFETCHSTAT_BUMP(zfetchstat_max_streams);
222 return;
223 }
224
225 zstream_t *zs = kmem_zalloc(sizeof (*zs), KM_SLEEP);
226 zs->zs_blkid = blkid;
227 zs->zs_pf_blkid = blkid;
228 zs->zs_ipf_blkid = blkid;
229 zs->zs_atime = now;
230 zs->zs_fetch = zf;
231 zfs_refcount_create(&zs->zs_blocks);
232 mutex_init(&zs->zs_lock, NULL, MUTEX_DEFAULT, NULL);
233 zf->zf_numstreams++;
234 list_insert_head(&zf->zf_stream, zs);
235 }
236
237 static void
dmu_zfetch_stream_done(void * arg,boolean_t io_issued)238 dmu_zfetch_stream_done(void *arg, boolean_t io_issued)
239 {
240 zstream_t *zs = arg;
241
242 if (zs->zs_start_time && io_issued) {
243 hrtime_t now = gethrtime();
244 hrtime_t delta = NSEC2USEC(now - zs->zs_start_time);
245
246 zs->zs_start_time = 0;
247 ZFETCHSTAT_SET(zfetchstat_last_completion_us, delta);
248 if (delta > ZFETCHSTAT_GET(zfetchstat_max_completion_us))
249 ZFETCHSTAT_SET(zfetchstat_max_completion_us, delta);
250 }
251
252 if (zfs_refcount_remove(&zs->zs_blocks, NULL) != 0)
253 return;
254
255 /*
256 * The parent fetch structure has gone away
257 */
258 if (zs->zs_fetch == NULL)
259 dmu_zfetch_stream_fini(zs);
260 }
261
262 /*
263 * This is the predictive prefetch entry point. It associates dnode access
264 * specified with blkid and nblks arguments with prefetch stream, predicts
265 * further accesses based on that stats and initiates speculative prefetch.
266 * fetch_data argument specifies whether actual data blocks should be fetched:
267 * FALSE -- prefetch only indirect blocks for predicted data blocks;
268 * TRUE -- prefetch predicted data blocks plus following indirect blocks.
269 */
270 void
dmu_zfetch(zfetch_t * zf,uint64_t blkid,uint64_t nblks,boolean_t fetch_data,boolean_t have_lock)271 dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks, boolean_t fetch_data,
272 boolean_t have_lock)
273 {
274 zstream_t *zs;
275 int64_t pf_start, ipf_start, ipf_istart, ipf_iend;
276 int64_t pf_ahead_blks, max_blks;
277 int epbs, max_dist_blks, pf_nblks, ipf_nblks, issued;
278 uint64_t end_of_access_blkid = blkid + nblks;
279 spa_t *spa = zf->zf_dnode->dn_objset->os_spa;
280
281 if (zfs_prefetch_disable)
282 return;
283
284 /*
285 * If we haven't yet loaded the indirect vdevs' mappings, we
286 * can only read from blocks that we carefully ensure are on
287 * concrete vdevs (or previously-loaded indirect vdevs). So we
288 * can't allow the predictive prefetcher to attempt reads of other
289 * blocks (e.g. of the MOS's dnode obejct).
290 */
291 if (!spa_indirect_vdevs_loaded(spa))
292 return;
293
294 /*
295 * As a fast path for small (single-block) files, ignore access
296 * to the first block.
297 */
298 if (!have_lock && blkid == 0)
299 return;
300
301 if (!have_lock)
302 rw_enter(&zf->zf_dnode->dn_struct_rwlock, RW_READER);
303
304
305 /*
306 * A fast path for small files for which no prefetch will
307 * happen.
308 */
309 if (zf->zf_dnode->dn_maxblkid < 2) {
310 if (!have_lock)
311 rw_exit(&zf->zf_dnode->dn_struct_rwlock);
312 return;
313 }
314 rw_enter(&zf->zf_rwlock, RW_READER);
315
316 /*
317 * Find matching prefetch stream. Depending on whether the accesses
318 * are block-aligned, first block of the new access may either follow
319 * the last block of the previous access, or be equal to it.
320 */
321 for (zs = list_head(&zf->zf_stream); zs != NULL;
322 zs = list_next(&zf->zf_stream, zs)) {
323 if (blkid == zs->zs_blkid || blkid + 1 == zs->zs_blkid) {
324 mutex_enter(&zs->zs_lock);
325 /*
326 * zs_blkid could have changed before we
327 * acquired zs_lock; re-check them here.
328 */
329 if (blkid == zs->zs_blkid) {
330 break;
331 } else if (blkid + 1 == zs->zs_blkid) {
332 blkid++;
333 nblks--;
334 if (nblks == 0) {
335 /* Already prefetched this before. */
336 mutex_exit(&zs->zs_lock);
337 rw_exit(&zf->zf_rwlock);
338 if (!have_lock) {
339 rw_exit(&zf->zf_dnode->
340 dn_struct_rwlock);
341 }
342 return;
343 }
344 break;
345 }
346 mutex_exit(&zs->zs_lock);
347 }
348 }
349
350 if (zs == NULL) {
351 /*
352 * This access is not part of any existing stream. Create
353 * a new stream for it.
354 */
355 ZFETCHSTAT_BUMP(zfetchstat_misses);
356 if (rw_tryupgrade(&zf->zf_rwlock))
357 dmu_zfetch_stream_create(zf, end_of_access_blkid);
358 rw_exit(&zf->zf_rwlock);
359 if (!have_lock)
360 rw_exit(&zf->zf_dnode->dn_struct_rwlock);
361 return;
362 }
363
364 /*
365 * This access was to a block that we issued a prefetch for on
366 * behalf of this stream. Issue further prefetches for this stream.
367 *
368 * Normally, we start prefetching where we stopped
369 * prefetching last (zs_pf_blkid). But when we get our first
370 * hit on this stream, zs_pf_blkid == zs_blkid, we don't
371 * want to prefetch the block we just accessed. In this case,
372 * start just after the block we just accessed.
373 */
374 pf_start = MAX(zs->zs_pf_blkid, end_of_access_blkid);
375
376 /*
377 * Double our amount of prefetched data, but don't let the
378 * prefetch get further ahead than zfetch_max_distance.
379 */
380 if (fetch_data) {
381 max_dist_blks =
382 zfetch_max_distance >> zf->zf_dnode->dn_datablkshift;
383 /*
384 * Previously, we were (zs_pf_blkid - blkid) ahead. We
385 * want to now be double that, so read that amount again,
386 * plus the amount we are catching up by (i.e. the amount
387 * read just now).
388 */
389 pf_ahead_blks = zs->zs_pf_blkid - blkid + nblks;
390 max_blks = max_dist_blks - (pf_start - end_of_access_blkid);
391 pf_nblks = MIN(pf_ahead_blks, max_blks);
392 } else {
393 pf_nblks = 0;
394 }
395
396 zs->zs_pf_blkid = pf_start + pf_nblks;
397
398 /*
399 * Do the same for indirects, starting from where we stopped last,
400 * or where we will stop reading data blocks (and the indirects
401 * that point to them).
402 */
403 ipf_start = MAX(zs->zs_ipf_blkid, zs->zs_pf_blkid);
404 max_dist_blks = zfetch_max_idistance >> zf->zf_dnode->dn_datablkshift;
405 /*
406 * We want to double our distance ahead of the data prefetch
407 * (or reader, if we are not prefetching data). Previously, we
408 * were (zs_ipf_blkid - blkid) ahead. To double that, we read
409 * that amount again, plus the amount we are catching up by
410 * (i.e. the amount read now + the amount of data prefetched now).
411 */
412 pf_ahead_blks = zs->zs_ipf_blkid - blkid + nblks + pf_nblks;
413 max_blks = max_dist_blks - (ipf_start - end_of_access_blkid);
414 ipf_nblks = MIN(pf_ahead_blks, max_blks);
415 zs->zs_ipf_blkid = ipf_start + ipf_nblks;
416
417 epbs = zf->zf_dnode->dn_indblkshift - SPA_BLKPTRSHIFT;
418 ipf_istart = P2ROUNDUP(ipf_start, 1 << epbs) >> epbs;
419 ipf_iend = P2ROUNDUP(zs->zs_ipf_blkid, 1 << epbs) >> epbs;
420
421 zs->zs_atime = gethrtime();
422 /* no prior reads in progress */
423 if (zfs_refcount_count(&zs->zs_blocks) == 0)
424 zs->zs_start_time = zs->zs_atime;
425 zs->zs_blkid = end_of_access_blkid;
426 zfs_refcount_add_few(&zs->zs_blocks, pf_nblks + ipf_iend - ipf_istart,
427 NULL);
428 mutex_exit(&zs->zs_lock);
429 rw_exit(&zf->zf_rwlock);
430 issued = 0;
431
432 /*
433 * dbuf_prefetch() is asynchronous (even when it needs to read
434 * indirect blocks), but we still prefer to drop our locks before
435 * calling it to reduce the time we hold them.
436 */
437
438 for (int i = 0; i < pf_nblks; i++) {
439 issued += dbuf_prefetch_impl(zf->zf_dnode, 0, pf_start + i,
440 ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH,
441 dmu_zfetch_stream_done, zs);
442 }
443 for (int64_t iblk = ipf_istart; iblk < ipf_iend; iblk++) {
444 issued += dbuf_prefetch_impl(zf->zf_dnode, 1, iblk,
445 ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH,
446 dmu_zfetch_stream_done, zs);
447 }
448 if (!have_lock)
449 rw_exit(&zf->zf_dnode->dn_struct_rwlock);
450 ZFETCHSTAT_BUMP(zfetchstat_hits);
451
452 if (issued)
453 ZFETCHSTAT_ADD(zfetchstat_io_issued, issued);
454 }
455