4 * The contents of this file are subject to the terms of the
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6 * You may not use this file except in compliance with the License.
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9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
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
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22 * Copyright 2009 Sun Microsystems, Inc. All rights reserved.
23 * Use is subject to license terms.
27 * Copyright (c) 2013, 2017 by Delphix. All rights reserved.
30 #include <sys/zfs_context.h>
31 #include <sys/dnode.h>
32 #include <sys/dmu_objset.h>
33 #include <sys/dmu_zfetch.h>
36 #include <sys/kstat.h>
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.
45 int zfs_prefetch_disable = B_FALSE;
47 /* max # of streams per zfetch */
48 unsigned int zfetch_max_streams = 8;
49 /* min time before stream reclaim */
50 unsigned int zfetch_min_sec_reap = 2;
51 /* max bytes to prefetch per stream (default 8MB) */
52 unsigned int zfetch_max_distance = 8 * 1024 * 1024;
53 /* max bytes to prefetch indirects for per stream (default 64MB) */
54 unsigned int zfetch_max_idistance = 64 * 1024 * 1024;
55 /* max number of bytes in an array_read in which we allow prefetching (1MB) */
56 unsigned long zfetch_array_rd_sz = 1024 * 1024;
58 typedef struct zfetch_stats {
59 kstat_named_t zfetchstat_hits;
60 kstat_named_t zfetchstat_misses;
61 kstat_named_t zfetchstat_max_streams;
64 static zfetch_stats_t zfetch_stats = {
65 { "hits", KSTAT_DATA_UINT64 },
66 { "misses", KSTAT_DATA_UINT64 },
67 { "max_streams", KSTAT_DATA_UINT64 },
70 #define ZFETCHSTAT_BUMP(stat) \
71 atomic_inc_64(&zfetch_stats.stat.value.ui64);
78 zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc",
79 KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t),
82 if (zfetch_ksp != NULL) {
83 zfetch_ksp->ks_data = &zfetch_stats;
84 kstat_install(zfetch_ksp);
91 if (zfetch_ksp != NULL) {
92 kstat_delete(zfetch_ksp);
98 * This takes a pointer to a zfetch structure and a dnode. It performs the
99 * necessary setup for the zfetch structure, grokking data from the
103 dmu_zfetch_init(zfetch_t *zf, dnode_t *dno)
110 list_create(&zf->zf_stream, sizeof (zstream_t),
111 offsetof(zstream_t, zs_node));
113 mutex_init(&zf->zf_lock, NULL, MUTEX_DEFAULT, NULL);
117 dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs)
119 ASSERT(MUTEX_HELD(&zf->zf_lock));
120 list_remove(&zf->zf_stream, zs);
121 mutex_destroy(&zs->zs_lock);
122 kmem_free(zs, sizeof (*zs));
126 * Clean-up state associated with a zfetch structure (e.g. destroy the
127 * streams). This doesn't free the zfetch_t itself, that's left to the caller.
130 dmu_zfetch_fini(zfetch_t *zf)
134 mutex_enter(&zf->zf_lock);
135 while ((zs = list_head(&zf->zf_stream)) != NULL)
136 dmu_zfetch_stream_remove(zf, zs);
137 mutex_exit(&zf->zf_lock);
138 list_destroy(&zf->zf_stream);
139 mutex_destroy(&zf->zf_lock);
145 * If there aren't too many streams already, create a new stream.
146 * The "blkid" argument is the next block that we expect this stream to access.
147 * While we're here, clean up old streams (which haven't been
148 * accessed for at least zfetch_min_sec_reap seconds).
151 dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid)
156 ASSERT(MUTEX_HELD(&zf->zf_lock));
159 * Clean up old streams.
161 for (zstream_t *zs = list_head(&zf->zf_stream);
162 zs != NULL; zs = zs_next) {
163 zs_next = list_next(&zf->zf_stream, zs);
164 if (((gethrtime() - zs->zs_atime) / NANOSEC) >
166 dmu_zfetch_stream_remove(zf, zs);
172 * The maximum number of streams is normally zfetch_max_streams,
173 * but for small files we lower it such that it's at least possible
174 * for all the streams to be non-overlapping.
176 * If we are already at the maximum number of streams for this file,
177 * even after removing old streams, then don't create this stream.
179 uint32_t max_streams = MAX(1, MIN(zfetch_max_streams,
180 zf->zf_dnode->dn_maxblkid * zf->zf_dnode->dn_datablksz /
181 zfetch_max_distance));
182 if (numstreams >= max_streams) {
183 ZFETCHSTAT_BUMP(zfetchstat_max_streams);
187 zstream_t *zs = kmem_zalloc(sizeof (*zs), KM_SLEEP);
188 zs->zs_blkid = blkid;
189 zs->zs_pf_blkid = blkid;
190 zs->zs_ipf_blkid = blkid;
191 zs->zs_atime = gethrtime();
192 mutex_init(&zs->zs_lock, NULL, MUTEX_DEFAULT, NULL);
194 list_insert_head(&zf->zf_stream, zs);
198 * This is the predictive prefetch entry point. It associates dnode access
199 * specified with blkid and nblks arguments with prefetch stream, predicts
200 * further accesses based on that stats and initiates speculative prefetch.
201 * fetch_data argument specifies whether actual data blocks should be fetched:
202 * FALSE -- prefetch only indirect blocks for predicted data blocks;
203 * TRUE -- prefetch predicted data blocks plus following indirect blocks.
206 dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks, boolean_t fetch_data,
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;
214 end_of_access_blkid = blkid + nblks;
215 spa_t *spa = zf->zf_dnode->dn_objset->os_spa;
217 if (zfs_prefetch_disable)
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 object).
226 if (!spa_indirect_vdevs_loaded(spa))
230 * As a fast path for small (single-block) files, ignore access
231 * to the first block.
237 rw_enter(&zf->zf_dnode->dn_struct_rwlock, RW_READER);
238 mutex_enter(&zf->zf_lock);
241 * Find matching prefetch stream. Depending on whether the accesses
242 * are block-aligned, first block of the new access may either follow
243 * the last block of the previous access, or be equal to it.
245 for (zs = list_head(&zf->zf_stream); zs != NULL;
246 zs = list_next(&zf->zf_stream, zs)) {
247 if (blkid == zs->zs_blkid || blkid + 1 == zs->zs_blkid) {
248 mutex_enter(&zs->zs_lock);
250 * zs_blkid could have changed before we
251 * acquired zs_lock; re-check them here.
253 if (blkid == zs->zs_blkid) {
255 } else if (blkid + 1 == zs->zs_blkid) {
259 /* Already prefetched this before. */
260 mutex_exit(&zs->zs_lock);
261 mutex_exit(&zf->zf_lock);
263 rw_exit(&zf->zf_dnode->
270 mutex_exit(&zs->zs_lock);
276 * This access is not part of any existing stream. Create
277 * a new stream for it.
279 ZFETCHSTAT_BUMP(zfetchstat_misses);
281 dmu_zfetch_stream_create(zf, end_of_access_blkid);
282 mutex_exit(&zf->zf_lock);
284 rw_exit(&zf->zf_dnode->dn_struct_rwlock);
289 * This access was to a block that we issued a prefetch for on
290 * behalf of this stream. Issue further prefetches for this stream.
292 * Normally, we start prefetching where we stopped
293 * prefetching last (zs_pf_blkid). But when we get our first
294 * hit on this stream, zs_pf_blkid == zs_blkid, we don't
295 * want to prefetch the block we just accessed. In this case,
296 * start just after the block we just accessed.
298 pf_start = MAX(zs->zs_pf_blkid, end_of_access_blkid);
301 * Double our amount of prefetched data, but don't let the
302 * prefetch get further ahead than zfetch_max_distance.
306 zfetch_max_distance >> zf->zf_dnode->dn_datablkshift;
308 * Previously, we were (zs_pf_blkid - blkid) ahead. We
309 * want to now be double that, so read that amount again,
310 * plus the amount we are catching up by (i.e. the amount
313 pf_ahead_blks = zs->zs_pf_blkid - blkid + nblks;
314 max_blks = max_dist_blks - (pf_start - end_of_access_blkid);
315 pf_nblks = MIN(pf_ahead_blks, max_blks);
320 zs->zs_pf_blkid = pf_start + pf_nblks;
323 * Do the same for indirects, starting from where we stopped last,
324 * or where we will stop reading data blocks (and the indirects
325 * that point to them).
327 ipf_start = MAX(zs->zs_ipf_blkid, zs->zs_pf_blkid);
328 max_dist_blks = zfetch_max_idistance >> zf->zf_dnode->dn_datablkshift;
330 * We want to double our distance ahead of the data prefetch
331 * (or reader, if we are not prefetching data). Previously, we
332 * were (zs_ipf_blkid - blkid) ahead. To double that, we read
333 * that amount again, plus the amount we are catching up by
334 * (i.e. the amount read now + the amount of data prefetched now).
336 pf_ahead_blks = zs->zs_ipf_blkid - blkid + nblks + pf_nblks;
337 max_blks = max_dist_blks - (ipf_start - end_of_access_blkid);
338 ipf_nblks = MIN(pf_ahead_blks, max_blks);
339 zs->zs_ipf_blkid = ipf_start + ipf_nblks;
341 epbs = zf->zf_dnode->dn_indblkshift - SPA_BLKPTRSHIFT;
342 ipf_istart = P2ROUNDUP(ipf_start, 1 << epbs) >> epbs;
343 ipf_iend = P2ROUNDUP(zs->zs_ipf_blkid, 1 << epbs) >> epbs;
345 zs->zs_atime = gethrtime();
346 zs->zs_blkid = end_of_access_blkid;
347 mutex_exit(&zs->zs_lock);
348 mutex_exit(&zf->zf_lock);
351 * dbuf_prefetch() is asynchronous (even when it needs to read
352 * indirect blocks), but we still prefer to drop our locks before
353 * calling it to reduce the time we hold them.
356 for (int i = 0; i < pf_nblks; i++) {
357 dbuf_prefetch(zf->zf_dnode, 0, pf_start + i,
358 ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH);
360 for (int64_t iblk = ipf_istart; iblk < ipf_iend; iblk++) {
361 dbuf_prefetch(zf->zf_dnode, 1, iblk,
362 ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH);
365 rw_exit(&zf->zf_dnode->dn_struct_rwlock);
366 ZFETCHSTAT_BUMP(zfetchstat_hits);
370 ZFS_MODULE_PARAM(zfs_prefetch, zfs_prefetch_, disable, INT, ZMOD_RW,
371 "Disable all ZFS prefetching");
373 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_streams, UINT, ZMOD_RW,
374 "Max number of streams per zfetch");
376 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, min_sec_reap, UINT, ZMOD_RW,
377 "Min time before stream reclaim");
379 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_distance, UINT, ZMOD_RW,
380 "Max bytes to prefetch per stream");
382 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_idistance, UINT, ZMOD_RW,
383 "Max bytes to prefetch indirects for per stream");
385 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, array_rd_sz, ULONG, ZMOD_RW,
386 "Number of bytes in a array_read");