1 // SPDX-License-Identifier: CDDL-1.0
2 /*
3 * This file and its contents are supplied under the terms of the
4 * Common Development and Distribution License ("CDDL"), version 1.0.
5 * You may only use this file in accordance with the terms of version
6 * 1.0 of the CDDL.
7 *
8 * A full copy of the text of the CDDL should have accompanied this
9 * source. A copy of the CDDL is also available via the Internet at
10 * https://opensource.org/license/CDDL-1.0.
11 */
12 /*
13 * Copyright 2009 Sun Microsystems, Inc. All rights reserved.
14 * Use is subject to license terms.
15 */
16
17 /*
18 * Copyright (c) 2013, 2017 by Delphix. All rights reserved.
19 */
20
21 #include <sys/zfs_context.h>
22 #include <sys/arc_impl.h>
23 #include <sys/dnode.h>
24 #include <sys/dmu_objset.h>
25 #include <sys/dmu_zfetch.h>
26 #include <sys/dmu.h>
27 #include <sys/dbuf.h>
28 #include <sys/kstat.h>
29 #include <sys/wmsum.h>
30
31 /*
32 * This tunable disables predictive prefetch. Note that it leaves "prescient"
33 * prefetch (e.g. prefetch for zfs send) intact. Unlike predictive prefetch,
34 * prescient prefetch never issues i/os that end up not being needed,
35 * so it can't hurt performance.
36 */
37
38 static int zfs_prefetch_disable = B_FALSE;
39
40 /* max # of streams per zfetch */
41 static unsigned int zfetch_max_streams = 8;
42 /* min time before stream reclaim */
43 static unsigned int zfetch_min_sec_reap = 1;
44 /* max time before stream delete */
45 static unsigned int zfetch_max_sec_reap = 2;
46 #ifdef _ILP32
47 /* min bytes to prefetch per stream (default 2MB) */
48 static unsigned int zfetch_min_distance = 2 * 1024 * 1024;
49 /* max bytes to prefetch per stream (default 8MB) */
50 unsigned int zfetch_max_distance = 8 * 1024 * 1024;
51 #else
52 /* min bytes to prefetch per stream (default 4MB) */
53 static unsigned int zfetch_min_distance = 4 * 1024 * 1024;
54 /* max bytes to prefetch per stream (default 64MB) */
55 unsigned int zfetch_max_distance = 64 * 1024 * 1024;
56 #endif
57 /* max bytes to prefetch indirects for per stream (default 128MB) */
58 unsigned int zfetch_max_idistance = 128 * 1024 * 1024;
59 /* max request reorder distance within a stream (default 16MB) */
60 unsigned int zfetch_max_reorder = 16 * 1024 * 1024;
61 /* Max log2 fraction of holes in a stream */
62 unsigned int zfetch_hole_shift = 2;
63
64 typedef struct zfetch_stats {
65 kstat_named_t zfetchstat_hits;
66 kstat_named_t zfetchstat_future;
67 kstat_named_t zfetchstat_stride;
68 kstat_named_t zfetchstat_past;
69 kstat_named_t zfetchstat_misses;
70 kstat_named_t zfetchstat_max_streams;
71 kstat_named_t zfetchstat_io_issued;
72 kstat_named_t zfetchstat_io_active;
73 } zfetch_stats_t;
74
75 static zfetch_stats_t zfetch_stats = {
76 { "hits", KSTAT_DATA_UINT64 },
77 { "future", KSTAT_DATA_UINT64 },
78 { "stride", KSTAT_DATA_UINT64 },
79 { "past", KSTAT_DATA_UINT64 },
80 { "misses", KSTAT_DATA_UINT64 },
81 { "max_streams", KSTAT_DATA_UINT64 },
82 { "io_issued", KSTAT_DATA_UINT64 },
83 { "io_active", KSTAT_DATA_UINT64 },
84 };
85
86 struct {
87 wmsum_t zfetchstat_hits;
88 wmsum_t zfetchstat_future;
89 wmsum_t zfetchstat_stride;
90 wmsum_t zfetchstat_past;
91 wmsum_t zfetchstat_misses;
92 wmsum_t zfetchstat_max_streams;
93 wmsum_t zfetchstat_io_issued;
94 aggsum_t zfetchstat_io_active;
95 } zfetch_sums;
96
97 #define ZFETCHSTAT_BUMP(stat) \
98 wmsum_add(&zfetch_sums.stat, 1)
99 #define ZFETCHSTAT_ADD(stat, val) \
100 wmsum_add(&zfetch_sums.stat, val)
101
102
103 static kstat_t *zfetch_ksp;
104
105 static int
zfetch_kstats_update(kstat_t * ksp,int rw)106 zfetch_kstats_update(kstat_t *ksp, int rw)
107 {
108 zfetch_stats_t *zs = ksp->ks_data;
109
110 if (rw == KSTAT_WRITE)
111 return (EACCES);
112 zs->zfetchstat_hits.value.ui64 =
113 wmsum_value(&zfetch_sums.zfetchstat_hits);
114 zs->zfetchstat_future.value.ui64 =
115 wmsum_value(&zfetch_sums.zfetchstat_future);
116 zs->zfetchstat_stride.value.ui64 =
117 wmsum_value(&zfetch_sums.zfetchstat_stride);
118 zs->zfetchstat_past.value.ui64 =
119 wmsum_value(&zfetch_sums.zfetchstat_past);
120 zs->zfetchstat_misses.value.ui64 =
121 wmsum_value(&zfetch_sums.zfetchstat_misses);
122 zs->zfetchstat_max_streams.value.ui64 =
123 wmsum_value(&zfetch_sums.zfetchstat_max_streams);
124 zs->zfetchstat_io_issued.value.ui64 =
125 wmsum_value(&zfetch_sums.zfetchstat_io_issued);
126 zs->zfetchstat_io_active.value.ui64 =
127 aggsum_value(&zfetch_sums.zfetchstat_io_active);
128 return (0);
129 }
130
131 void
zfetch_init(void)132 zfetch_init(void)
133 {
134 wmsum_init(&zfetch_sums.zfetchstat_hits, 0);
135 wmsum_init(&zfetch_sums.zfetchstat_future, 0);
136 wmsum_init(&zfetch_sums.zfetchstat_stride, 0);
137 wmsum_init(&zfetch_sums.zfetchstat_past, 0);
138 wmsum_init(&zfetch_sums.zfetchstat_misses, 0);
139 wmsum_init(&zfetch_sums.zfetchstat_max_streams, 0);
140 wmsum_init(&zfetch_sums.zfetchstat_io_issued, 0);
141 aggsum_init(&zfetch_sums.zfetchstat_io_active, 0);
142
143 zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc",
144 KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t),
145 KSTAT_FLAG_VIRTUAL);
146
147 if (zfetch_ksp != NULL) {
148 zfetch_ksp->ks_data = &zfetch_stats;
149 zfetch_ksp->ks_update = zfetch_kstats_update;
150 kstat_install(zfetch_ksp);
151 }
152 }
153
154 void
zfetch_fini(void)155 zfetch_fini(void)
156 {
157 if (zfetch_ksp != NULL) {
158 kstat_delete(zfetch_ksp);
159 zfetch_ksp = NULL;
160 }
161
162 wmsum_fini(&zfetch_sums.zfetchstat_hits);
163 wmsum_fini(&zfetch_sums.zfetchstat_future);
164 wmsum_fini(&zfetch_sums.zfetchstat_stride);
165 wmsum_fini(&zfetch_sums.zfetchstat_past);
166 wmsum_fini(&zfetch_sums.zfetchstat_misses);
167 wmsum_fini(&zfetch_sums.zfetchstat_max_streams);
168 wmsum_fini(&zfetch_sums.zfetchstat_io_issued);
169 ASSERT0(aggsum_value(&zfetch_sums.zfetchstat_io_active));
170 aggsum_fini(&zfetch_sums.zfetchstat_io_active);
171 }
172
173 /*
174 * This takes a pointer to a zfetch structure and a dnode. It performs the
175 * necessary setup for the zfetch structure, grokking data from the
176 * associated dnode.
177 */
178 void
dmu_zfetch_init(zfetch_t * zf,dnode_t * dno)179 dmu_zfetch_init(zfetch_t *zf, dnode_t *dno)
180 {
181 if (zf == NULL)
182 return;
183 zf->zf_dnode = dno;
184 zf->zf_numstreams = 0;
185
186 list_create(&zf->zf_stream, sizeof (zstream_t),
187 offsetof(zstream_t, zs_node));
188
189 mutex_init(&zf->zf_lock, NULL, MUTEX_DEFAULT, NULL);
190 }
191
192 static void
dmu_zfetch_stream_fini(zstream_t * zs)193 dmu_zfetch_stream_fini(zstream_t *zs)
194 {
195 ASSERT(!list_link_active(&zs->zs_node));
196 zfs_refcount_destroy(&zs->zs_callers);
197 zfs_refcount_destroy(&zs->zs_refs);
198 kmem_free(zs, sizeof (*zs));
199 }
200
201 static void
dmu_zfetch_stream_remove(zfetch_t * zf,zstream_t * zs)202 dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs)
203 {
204 ASSERT(MUTEX_HELD(&zf->zf_lock));
205 list_remove(&zf->zf_stream, zs);
206 zf->zf_numstreams--;
207 membar_producer();
208 if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0)
209 dmu_zfetch_stream_fini(zs);
210 }
211
212 /*
213 * Clean-up state associated with a zfetch structure (e.g. destroy the
214 * streams). This doesn't free the zfetch_t itself, that's left to the caller.
215 */
216 void
dmu_zfetch_fini(zfetch_t * zf)217 dmu_zfetch_fini(zfetch_t *zf)
218 {
219 zstream_t *zs;
220
221 mutex_enter(&zf->zf_lock);
222 while ((zs = list_head(&zf->zf_stream)) != NULL)
223 dmu_zfetch_stream_remove(zf, zs);
224 mutex_exit(&zf->zf_lock);
225 list_destroy(&zf->zf_stream);
226 mutex_destroy(&zf->zf_lock);
227
228 zf->zf_dnode = NULL;
229 }
230
231 /*
232 * If there aren't too many active streams already, create one more.
233 * In process delete/reuse all streams without hits for zfetch_max_sec_reap.
234 * If needed, reuse oldest stream without hits for zfetch_min_sec_reap or ever.
235 * The "blkid" argument is the next block that we expect this stream to access.
236 */
237 static zstream_t *
dmu_zfetch_stream_create(zfetch_t * zf,uint64_t blkid)238 dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid)
239 {
240 zstream_t *zs, *zs_next, *zs_old = NULL;
241 uint_t now = gethrestime_sec(), t;
242
243 ASSERT(MUTEX_HELD(&zf->zf_lock));
244
245 /*
246 * Delete too old streams, reusing the first found one.
247 */
248 t = now - zfetch_max_sec_reap;
249 for (zs = list_head(&zf->zf_stream); zs != NULL; zs = zs_next) {
250 zs_next = list_next(&zf->zf_stream, zs);
251 /*
252 * Skip if still active. 1 -- zf_stream reference.
253 */
254 if ((int)(zs->zs_atime - t) >= 0)
255 continue;
256 if (zfs_refcount_count(&zs->zs_refs) != 1)
257 continue;
258 if (zs_old)
259 dmu_zfetch_stream_remove(zf, zs);
260 else
261 zs_old = zs;
262 }
263 if (zs_old) {
264 zs = zs_old;
265 list_remove(&zf->zf_stream, zs);
266 goto reuse;
267 }
268
269 /*
270 * The maximum number of streams is normally zfetch_max_streams,
271 * but for small files we lower it such that it's at least possible
272 * for all the streams to be non-overlapping.
273 */
274 uint32_t max_streams = MAX(1, MIN(zfetch_max_streams,
275 (zf->zf_dnode->dn_maxblkid << zf->zf_dnode->dn_datablkshift) /
276 zfetch_max_distance));
277 if (zf->zf_numstreams >= max_streams) {
278 t = now - zfetch_min_sec_reap;
279 for (zs = list_head(&zf->zf_stream); zs != NULL;
280 zs = list_next(&zf->zf_stream, zs)) {
281 if ((int)(zs->zs_atime - t) >= 0)
282 continue;
283 if (zfs_refcount_count(&zs->zs_refs) != 1)
284 continue;
285 if (zs_old == NULL ||
286 (int)(zs_old->zs_atime - zs->zs_atime) >= 0)
287 zs_old = zs;
288 }
289 if (zs_old) {
290 zs = zs_old;
291 list_remove(&zf->zf_stream, zs);
292 goto reuse;
293 }
294 ZFETCHSTAT_BUMP(zfetchstat_max_streams);
295 return (NULL);
296 }
297
298 zs = kmem_zalloc(sizeof (*zs), KM_SLEEP);
299 zfs_refcount_create(&zs->zs_callers);
300 zfs_refcount_create(&zs->zs_refs);
301 /* One reference for zf_stream. */
302 zfs_refcount_add(&zs->zs_refs, NULL);
303 zf->zf_numstreams++;
304
305 reuse:
306 list_insert_head(&zf->zf_stream, zs);
307 zs->zs_blkid = blkid;
308 /* Allow immediate stream reuse until first hit. */
309 zs->zs_atime = now - zfetch_min_sec_reap;
310 memset(zs->zs_ranges, 0, sizeof (zs->zs_ranges));
311 zs->zs_pf_dist = 0;
312 zs->zs_ipf_dist = 0;
313 zs->zs_pf_start = blkid;
314 zs->zs_pf_end = blkid;
315 zs->zs_ipf_start = blkid;
316 zs->zs_ipf_end = blkid;
317 zs->zs_missed = B_FALSE;
318 zs->zs_more = B_FALSE;
319 return (zs);
320 }
321
322 static void
dmu_zfetch_done(void * arg,uint64_t level,uint64_t blkid,boolean_t io_issued)323 dmu_zfetch_done(void *arg, uint64_t level, uint64_t blkid, boolean_t io_issued)
324 {
325 zstream_t *zs = arg;
326
327 if (io_issued && level == 0 && blkid < zs->zs_blkid)
328 zs->zs_more = B_TRUE;
329 if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0)
330 dmu_zfetch_stream_fini(zs);
331 aggsum_add(&zfetch_sums.zfetchstat_io_active, -1);
332 }
333
334 /*
335 * Process stream hit access for nblks blocks starting at zs_blkid. Return
336 * number of blocks to proceed for after aggregation with future ranges.
337 */
338 static uint64_t
dmu_zfetch_hit(zstream_t * zs,uint64_t nblks)339 dmu_zfetch_hit(zstream_t *zs, uint64_t nblks)
340 {
341 uint_t i, j;
342
343 /* Optimize sequential accesses (no future ranges). */
344 if (zs->zs_ranges[0].start == 0)
345 goto done;
346
347 /* Look for intersections with further ranges. */
348 for (i = 0; i < ZFETCH_RANGES; i++) {
349 zsrange_t *r = &zs->zs_ranges[i];
350 if (r->start == 0 || r->start > nblks)
351 break;
352 if (r->end >= nblks) {
353 nblks = r->end;
354 i++;
355 break;
356 }
357 }
358
359 /* Delete all found intersecting ranges, updates remaining. */
360 for (j = 0; i < ZFETCH_RANGES; i++, j++) {
361 if (zs->zs_ranges[i].start == 0)
362 break;
363 ASSERT3U(zs->zs_ranges[i].start, >, nblks);
364 ASSERT3U(zs->zs_ranges[i].end, >, nblks);
365 zs->zs_ranges[j].start = zs->zs_ranges[i].start - nblks;
366 zs->zs_ranges[j].end = zs->zs_ranges[i].end - nblks;
367 }
368 if (j < ZFETCH_RANGES) {
369 zs->zs_ranges[j].start = 0;
370 zs->zs_ranges[j].end = 0;
371 }
372
373 done:
374 zs->zs_blkid += nblks;
375 return (nblks);
376 }
377
378 /*
379 * Process future stream access for nblks blocks starting at blkid. Return
380 * number of blocks to proceed for if future ranges reach fill threshold.
381 */
382 static uint64_t
dmu_zfetch_future(zstream_t * zs,uint64_t blkid,uint64_t nblks)383 dmu_zfetch_future(zstream_t *zs, uint64_t blkid, uint64_t nblks)
384 {
385 ASSERT3U(blkid, >, zs->zs_blkid);
386 blkid -= zs->zs_blkid;
387 ASSERT3U(blkid + nblks, <=, UINT16_MAX);
388
389 /* Search for first and last intersection or insert point. */
390 uint_t f = ZFETCH_RANGES, l = 0, i;
391 for (i = 0; i < ZFETCH_RANGES; i++) {
392 zsrange_t *r = &zs->zs_ranges[i];
393 if (r->start == 0 || r->start > blkid + nblks)
394 break;
395 if (r->end < blkid)
396 continue;
397 if (f > i)
398 f = i;
399 if (l < i)
400 l = i;
401 }
402 if (f <= l) {
403 /* Got some intersecting range, expand it if needed. */
404 if (zs->zs_ranges[f].start > blkid)
405 zs->zs_ranges[f].start = blkid;
406 zs->zs_ranges[f].end = MAX(zs->zs_ranges[l].end, blkid + nblks);
407 if (f < l) {
408 /* Got more than one intersection, remove others. */
409 for (f++, l++; l < ZFETCH_RANGES; f++, l++) {
410 zs->zs_ranges[f].start = zs->zs_ranges[l].start;
411 zs->zs_ranges[f].end = zs->zs_ranges[l].end;
412 }
413 zs->zs_ranges[f].start = 0;
414 zs->zs_ranges[f].end = 0;
415 }
416 } else if (i < ZFETCH_RANGES) {
417 /* Got no intersecting ranges, insert new one. */
418 for (l = ZFETCH_RANGES - 1; l > i; l--) {
419 zs->zs_ranges[l].start = zs->zs_ranges[l - 1].start;
420 zs->zs_ranges[l].end = zs->zs_ranges[l - 1].end;
421 }
422 zs->zs_ranges[i].start = blkid;
423 zs->zs_ranges[i].end = blkid + nblks;
424 } else {
425 /* No space left to insert. Drop the range. */
426 return (0);
427 }
428
429 /* Check if with the new access addition we reached fill threshold. */
430 if (zfetch_hole_shift >= 16)
431 return (0);
432 uint_t hole = 0;
433 for (i = f = l = 0; i < ZFETCH_RANGES; i++) {
434 zsrange_t *r = &zs->zs_ranges[i];
435 if (r->start == 0)
436 break;
437 hole += r->start - f;
438 f = r->end;
439 if (hole <= r->end >> zfetch_hole_shift)
440 l = r->end;
441 }
442 if (l > 0)
443 return (dmu_zfetch_hit(zs, l));
444
445 return (0);
446 }
447
448 /*
449 * Prime a zfetch stream at blkid, so that the first demand access triggered
450 * enough prefetch without ramp-up to sequentially read up to end_blkid.
451 */
452 boolean_t
dmu_zfetch_prime(zfetch_t * zf,uint64_t blkid,uint64_t end_blkid)453 dmu_zfetch_prime(zfetch_t *zf, uint64_t blkid, uint64_t end_blkid)
454 {
455 zstream_t *zs;
456 dnode_t *dn = zf->zf_dnode;
457 spa_t *spa = dn->dn_objset->os_spa;
458
459 ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));
460 if (zfs_prefetch_disable ||
461 dn->dn_objset->os_prefetch == ZFS_PREFETCH_NONE)
462 return (B_FALSE);
463
464 if (!spa_indirect_vdevs_loaded(spa))
465 return (B_FALSE);
466
467 uint64_t maxblkid = dn->dn_maxblkid;
468 unsigned int dbs = dn->dn_datablkshift;
469
470 if (blkid >= maxblkid)
471 return (B_FALSE);
472 if (end_blkid > maxblkid + 1)
473 end_blkid = maxblkid + 1;
474
475 mutex_enter(&zf->zf_lock);
476
477 /* Skip if a nearby stream already covers this range. */
478 uint_t max_near = zfetch_max_reorder >> dbs;
479 for (zs = list_head(&zf->zf_stream); zs != NULL;
480 zs = list_next(&zf->zf_stream, zs)) {
481 uint64_t diff = (blkid >= zs->zs_blkid) ?
482 (blkid - zs->zs_blkid) : (zs->zs_blkid - blkid);
483 if (diff <= max_near) {
484 mutex_exit(&zf->zf_lock);
485 return (B_FALSE);
486 }
487 }
488
489 /* Skip if at stream limit and none are reclaimable. */
490 zs = dmu_zfetch_stream_create(zf, blkid);
491 if (zs == NULL) {
492 mutex_exit(&zf->zf_lock);
493 return (B_FALSE);
494 }
495 ASSERT3U(zs->zs_blkid, ==, blkid);
496
497 /* dmu_zfetch_prepare() will double the distances, so take a half. */
498 unsigned int nbytes = ((end_blkid - blkid) << dbs) / 2;
499 zs->zs_pf_dist = MIN(nbytes, zfetch_min_distance);
500 zs->zs_ipf_dist = MIN(nbytes, zfetch_max_idistance);
501
502 mutex_exit(&zf->zf_lock);
503 return (B_TRUE);
504 }
505
506 /*
507 * This is the predictive prefetch entry point. dmu_zfetch_prepare()
508 * associates dnode access specified with blkid and nblks arguments with
509 * prefetch stream, predicts further accesses based on that stats and returns
510 * the stream pointer on success. That pointer must later be passed to
511 * dmu_zfetch_run() to initiate the speculative prefetch for the stream and
512 * release it. dmu_zfetch() is a wrapper for simple cases when window between
513 * prediction and prefetch initiation is not needed.
514 * fetch_data argument specifies whether actual data blocks should be fetched:
515 * FALSE -- prefetch only indirect blocks for predicted data blocks;
516 * TRUE -- prefetch predicted data blocks plus following indirect blocks.
517 */
518 zstream_t *
dmu_zfetch_prepare(zfetch_t * zf,uint64_t blkid,uint64_t nblks,boolean_t fetch_data,boolean_t have_lock)519 dmu_zfetch_prepare(zfetch_t *zf, uint64_t blkid, uint64_t nblks,
520 boolean_t fetch_data, boolean_t have_lock)
521 {
522 zstream_t *zs;
523 spa_t *spa = zf->zf_dnode->dn_objset->os_spa;
524 zfs_prefetch_type_t os_prefetch = zf->zf_dnode->dn_objset->os_prefetch;
525 int64_t ipf_start, ipf_end;
526
527 if (zfs_prefetch_disable || os_prefetch == ZFS_PREFETCH_NONE)
528 return (NULL);
529
530 if (os_prefetch == ZFS_PREFETCH_METADATA)
531 fetch_data = B_FALSE;
532
533 /*
534 * If we haven't yet loaded the indirect vdevs' mappings, we
535 * can only read from blocks that we carefully ensure are on
536 * concrete vdevs (or previously-loaded indirect vdevs). So we
537 * can't allow the predictive prefetcher to attempt reads of other
538 * blocks (e.g. of the MOS's dnode object).
539 */
540 if (!spa_indirect_vdevs_loaded(spa))
541 return (NULL);
542
543 /*
544 * As a fast path for small (single-block) files, ignore access
545 * to the first block, unless some streams exist, since a prime
546 * may be waiting.
547 */
548 if (!have_lock && blkid == 0 && zf->zf_numstreams == 0)
549 return (NULL);
550
551 if (!have_lock)
552 rw_enter(&zf->zf_dnode->dn_struct_rwlock, RW_READER);
553
554 /*
555 * A fast path for small files for which no prefetch will happen,
556 * unless streams exist, since a prime may be waiting.
557 */
558 uint64_t maxblkid = zf->zf_dnode->dn_maxblkid;
559 if (maxblkid < 2 && (maxblkid == 0 || zf->zf_numstreams == 0)) {
560 if (!have_lock)
561 rw_exit(&zf->zf_dnode->dn_struct_rwlock);
562 return (NULL);
563 }
564 mutex_enter(&zf->zf_lock);
565
566 /*
567 * Find perfect prefetch stream. Depending on whether the accesses
568 * are block-aligned, first block of the new access may either follow
569 * the last block of the previous access, or be equal to it.
570 */
571 unsigned int dbs = zf->zf_dnode->dn_datablkshift;
572 uint64_t end_blkid = blkid + nblks;
573 for (zs = list_head(&zf->zf_stream); zs != NULL;
574 zs = list_next(&zf->zf_stream, zs)) {
575 if (blkid == zs->zs_blkid) {
576 goto hit;
577 } else if (blkid + 1 == zs->zs_blkid) {
578 blkid++;
579 nblks--;
580 goto hit;
581 }
582 }
583
584 /*
585 * Find close enough prefetch stream. Access crossing stream position
586 * is a hit in its new part. Access ahead of stream position considered
587 * a hit for metadata prefetch, since we do not care about fill percent,
588 * or stored for future otherwise. Access behind stream position is
589 * silently ignored, since we already skipped it reaching fill percent.
590 */
591 uint_t max_reorder = MIN((zfetch_max_reorder >> dbs) + 1, UINT16_MAX);
592 uint_t t = gethrestime_sec() - zfetch_max_sec_reap;
593 for (zs = list_head(&zf->zf_stream); zs != NULL;
594 zs = list_next(&zf->zf_stream, zs)) {
595 if (blkid > zs->zs_blkid) {
596 if (end_blkid <= zs->zs_blkid + max_reorder) {
597 if (!fetch_data) {
598 nblks = dmu_zfetch_hit(zs,
599 end_blkid - zs->zs_blkid);
600 ZFETCHSTAT_BUMP(zfetchstat_stride);
601 goto future;
602 }
603 nblks = dmu_zfetch_future(zs, blkid, nblks);
604 if (nblks > 0)
605 ZFETCHSTAT_BUMP(zfetchstat_stride);
606 else
607 ZFETCHSTAT_BUMP(zfetchstat_future);
608 goto future;
609 }
610 } else if (end_blkid >= zs->zs_blkid) {
611 nblks -= zs->zs_blkid - blkid;
612 blkid += zs->zs_blkid - blkid;
613 goto hit;
614 } else if (end_blkid + max_reorder > zs->zs_blkid &&
615 (int)(zs->zs_atime - t) >= 0) {
616 ZFETCHSTAT_BUMP(zfetchstat_past);
617 zs->zs_atime = gethrestime_sec();
618 goto out;
619 }
620 }
621
622 /*
623 * This access is not part of any existing stream. Create a new
624 * stream for it unless we are at the end of file.
625 */
626 ASSERT0P(zs);
627 if (end_blkid < maxblkid)
628 (void) dmu_zfetch_stream_create(zf, end_blkid);
629 mutex_exit(&zf->zf_lock);
630 ZFETCHSTAT_BUMP(zfetchstat_misses);
631 ipf_start = 0;
632 goto prescient;
633
634 hit:
635 nblks = dmu_zfetch_hit(zs, nblks);
636 ZFETCHSTAT_BUMP(zfetchstat_hits);
637
638 future:
639 zs->zs_atime = gethrestime_sec();
640
641 /* Exit if we already prefetched for this position before. */
642 if (nblks == 0 && zs->zs_ipf_end > end_blkid)
643 goto out;
644
645 /* If the file is ending, remove the stream. */
646 end_blkid = zs->zs_blkid;
647 if (end_blkid >= maxblkid) {
648 dmu_zfetch_stream_remove(zf, zs);
649 out:
650 mutex_exit(&zf->zf_lock);
651 if (!have_lock)
652 rw_exit(&zf->zf_dnode->dn_struct_rwlock);
653 return (NULL);
654 }
655
656 /*
657 * This access was to a block that we issued a prefetch for on
658 * behalf of this stream. Calculate further prefetch distances.
659 *
660 * Start prefetch from the demand access size (nblks). Double the
661 * distance every access up to zfetch_min_distance. After that only
662 * if needed increase the distance by 1/8 up to zfetch_max_distance.
663 *
664 * Don't double the distance beyond single block if we have more
665 * than ~6% of ARC held by active prefetches. It should help with
666 * getting out of RAM on some badly mispredicted read patterns.
667 */
668 unsigned int nbytes = nblks << dbs;
669 unsigned int pf_nblks;
670 if (fetch_data) {
671 if (unlikely(zs->zs_pf_dist < nbytes))
672 zs->zs_pf_dist = nbytes;
673 else if (zs->zs_pf_dist < zfetch_min_distance &&
674 (zs->zs_pf_dist < (1 << dbs) ||
675 aggsum_compare(&zfetch_sums.zfetchstat_io_active,
676 arc_c_max >> (4 + dbs)) < 0))
677 zs->zs_pf_dist *= 2;
678 else if (zs->zs_more)
679 zs->zs_pf_dist += zs->zs_pf_dist / 8;
680 zs->zs_more = B_FALSE;
681 if (zs->zs_pf_dist > zfetch_max_distance)
682 zs->zs_pf_dist = zfetch_max_distance;
683 pf_nblks = zs->zs_pf_dist >> dbs;
684 } else {
685 pf_nblks = 0;
686 }
687 if (zs->zs_pf_start < end_blkid)
688 zs->zs_pf_start = end_blkid;
689 if (zs->zs_pf_end < end_blkid + pf_nblks)
690 zs->zs_pf_end = end_blkid + pf_nblks;
691
692 /*
693 * Do the same for indirects, starting where we will stop reading
694 * data blocks (and the indirects that point to them).
695 */
696 nbytes = MAX(nbytes, (1 << dbs));
697 if (unlikely(zs->zs_ipf_dist < nbytes))
698 zs->zs_ipf_dist = nbytes;
699 else
700 zs->zs_ipf_dist *= 2;
701 if (zs->zs_ipf_dist > zfetch_max_idistance)
702 zs->zs_ipf_dist = zfetch_max_idistance;
703 pf_nblks = zs->zs_ipf_dist >> dbs;
704 if (zs->zs_ipf_start < zs->zs_pf_end)
705 zs->zs_ipf_start = zs->zs_pf_end;
706 ipf_start = zs->zs_ipf_end;
707 if (zs->zs_ipf_end < zs->zs_pf_end + pf_nblks)
708 zs->zs_ipf_end = zs->zs_pf_end + pf_nblks;
709
710 zfs_refcount_add(&zs->zs_refs, NULL);
711 /* Count concurrent callers. */
712 zfs_refcount_add(&zs->zs_callers, NULL);
713 mutex_exit(&zf->zf_lock);
714
715 prescient:
716 /*
717 * Prefetch the following indirect blocks for this access to reduce
718 * dbuf_hold() sync read delays in dmu_buf_hold_array_by_dnode().
719 * This covers the gap during the first couple accesses when we can
720 * not predict the future yet, but know what is needed right now.
721 * This should be very rare for reads/writes to need more than one
722 * indirect, but more useful for cloning due to much bigger accesses.
723 */
724 ipf_start = MAX(ipf_start, blkid + 1);
725 int epbs = zf->zf_dnode->dn_indblkshift - SPA_BLKPTRSHIFT;
726 ipf_start = P2ROUNDUP(ipf_start, 1 << epbs) >> epbs;
727 ipf_end = P2ROUNDUP(end_blkid, 1 << epbs) >> epbs;
728
729 int issued = 0;
730 for (int64_t iblk = ipf_start; iblk < ipf_end; iblk++) {
731 issued += dbuf_prefetch(zf->zf_dnode, 1, iblk,
732 ZIO_PRIORITY_SYNC_READ, ARC_FLAG_PRESCIENT_PREFETCH);
733 }
734
735 if (!have_lock)
736 rw_exit(&zf->zf_dnode->dn_struct_rwlock);
737 if (issued)
738 ZFETCHSTAT_ADD(zfetchstat_io_issued, issued);
739 return (zs);
740 }
741
742 void
dmu_zfetch_run(zfetch_t * zf,zstream_t * zs,boolean_t missed,boolean_t have_lock,boolean_t uncached)743 dmu_zfetch_run(zfetch_t *zf, zstream_t *zs, boolean_t missed,
744 boolean_t have_lock, boolean_t uncached)
745 {
746 int64_t pf_start, pf_end, ipf_start, ipf_end;
747 int epbs, issued;
748
749 if (missed)
750 zs->zs_missed = missed;
751
752 /*
753 * Postpone the prefetch if there are more concurrent callers.
754 * It happens when multiple requests are waiting for the same
755 * indirect block. The last one will run the prefetch for all.
756 */
757 if (zfs_refcount_remove(&zs->zs_callers, NULL) != 0) {
758 /* Drop reference taken in dmu_zfetch_prepare(). */
759 if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0)
760 dmu_zfetch_stream_fini(zs);
761 return;
762 }
763
764 mutex_enter(&zf->zf_lock);
765 if (zs->zs_missed) {
766 pf_start = zs->zs_pf_start;
767 pf_end = zs->zs_pf_start = zs->zs_pf_end;
768 } else {
769 pf_start = pf_end = 0;
770 }
771 ipf_start = zs->zs_ipf_start;
772 ipf_end = zs->zs_ipf_start = zs->zs_ipf_end;
773 mutex_exit(&zf->zf_lock);
774 ASSERT3S(pf_start, <=, pf_end);
775 ASSERT3S(ipf_start, <=, ipf_end);
776
777 epbs = zf->zf_dnode->dn_indblkshift - SPA_BLKPTRSHIFT;
778 ipf_start = P2ROUNDUP(ipf_start, 1 << epbs) >> epbs;
779 ipf_end = P2ROUNDUP(ipf_end, 1 << epbs) >> epbs;
780 ASSERT3S(ipf_start, <=, ipf_end);
781 issued = pf_end - pf_start + ipf_end - ipf_start;
782 if (issued > 1) {
783 /* More references on top of taken in dmu_zfetch_prepare(). */
784 zfs_refcount_add_few(&zs->zs_refs, issued - 1, NULL);
785 } else if (issued == 0) {
786 /* Some other thread has done our work, so drop the ref. */
787 if (zfs_refcount_remove(&zs->zs_refs, NULL) == 0)
788 dmu_zfetch_stream_fini(zs);
789 return;
790 }
791 aggsum_add(&zfetch_sums.zfetchstat_io_active, issued);
792
793 if (!have_lock)
794 rw_enter(&zf->zf_dnode->dn_struct_rwlock, RW_READER);
795
796 issued = 0;
797 for (int64_t blk = pf_start; blk < pf_end; blk++) {
798 issued += dbuf_prefetch_impl(zf->zf_dnode, 0, blk,
799 ZIO_PRIORITY_ASYNC_READ, uncached ?
800 ARC_FLAG_UNCACHED : 0, dmu_zfetch_done, zs);
801 }
802 for (int64_t iblk = ipf_start; iblk < ipf_end; iblk++) {
803 issued += dbuf_prefetch_impl(zf->zf_dnode, 1, iblk,
804 ZIO_PRIORITY_ASYNC_READ, 0, dmu_zfetch_done, zs);
805 }
806
807 if (!have_lock)
808 rw_exit(&zf->zf_dnode->dn_struct_rwlock);
809
810 if (issued)
811 ZFETCHSTAT_ADD(zfetchstat_io_issued, issued);
812 }
813
814 void
dmu_zfetch(zfetch_t * zf,uint64_t blkid,uint64_t nblks,boolean_t fetch_data,boolean_t missed,boolean_t have_lock,boolean_t uncached)815 dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks, boolean_t fetch_data,
816 boolean_t missed, boolean_t have_lock, boolean_t uncached)
817 {
818 zstream_t *zs;
819
820 zs = dmu_zfetch_prepare(zf, blkid, nblks, fetch_data, have_lock);
821 if (zs)
822 dmu_zfetch_run(zf, zs, missed, have_lock, uncached);
823 }
824
825 ZFS_MODULE_PARAM(zfs_prefetch, zfs_prefetch_, disable, INT, ZMOD_RW,
826 "Disable all ZFS prefetching");
827
828 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_streams, UINT, ZMOD_RW,
829 "Max number of streams per zfetch");
830
831 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, min_sec_reap, UINT, ZMOD_RW,
832 "Min time before stream reclaim");
833
834 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_sec_reap, UINT, ZMOD_RW,
835 "Max time before stream delete");
836
837 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, min_distance, UINT, ZMOD_RW,
838 "Min bytes to prefetch per stream");
839
840 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_distance, UINT, ZMOD_RW,
841 "Max bytes to prefetch per stream");
842
843 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_idistance, UINT, ZMOD_RW,
844 "Max bytes to prefetch indirects for per stream");
845
846 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_reorder, UINT, ZMOD_RW,
847 "Max request reorder distance within a stream");
848
849 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, hole_shift, UINT, ZMOD_RW,
850 "Max log2 fraction of holes in a stream");
851