xref: /titanic_41/usr/src/uts/common/fs/zfs/dmu_zfetch.c (revision 5f9bb2f350e19a276d3aff33afb5fc94fb47f02a)
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 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  * I'm against tune-ables, but these should probably exist as tweakable globals
40  * until we can get this working the way we want it to.
41  */
42 
43 int zfs_prefetch_disable = 0;
44 
45 /* max # of streams per zfetch */
46 uint32_t	zfetch_max_streams = 8;
47 /* min time before stream reclaim */
48 uint32_t	zfetch_min_sec_reap = 2;
49 /* max number of blocks to fetch at a time */
50 uint32_t	zfetch_block_cap = 256;
51 /* number of bytes in a array_read at which we stop prefetching (1Mb) */
52 uint64_t	zfetch_array_rd_sz = 1024 * 1024;
53 
54 /* forward decls for static routines */
55 static boolean_t	dmu_zfetch_colinear(zfetch_t *, zstream_t *);
56 static void		dmu_zfetch_dofetch(zfetch_t *, zstream_t *);
57 static uint64_t		dmu_zfetch_fetch(dnode_t *, uint64_t, uint64_t);
58 static uint64_t		dmu_zfetch_fetchsz(dnode_t *, uint64_t, uint64_t);
59 static boolean_t	dmu_zfetch_find(zfetch_t *, zstream_t *, int);
60 static int		dmu_zfetch_stream_insert(zfetch_t *, zstream_t *);
61 static zstream_t	*dmu_zfetch_stream_reclaim(zfetch_t *);
62 static void		dmu_zfetch_stream_remove(zfetch_t *, zstream_t *);
63 static int		dmu_zfetch_streams_equal(zstream_t *, zstream_t *);
64 
65 typedef struct zfetch_stats {
66 	kstat_named_t zfetchstat_hits;
67 	kstat_named_t zfetchstat_misses;
68 	kstat_named_t zfetchstat_colinear_hits;
69 	kstat_named_t zfetchstat_colinear_misses;
70 	kstat_named_t zfetchstat_stride_hits;
71 	kstat_named_t zfetchstat_stride_misses;
72 	kstat_named_t zfetchstat_reclaim_successes;
73 	kstat_named_t zfetchstat_reclaim_failures;
74 	kstat_named_t zfetchstat_stream_resets;
75 	kstat_named_t zfetchstat_stream_noresets;
76 	kstat_named_t zfetchstat_bogus_streams;
77 } zfetch_stats_t;
78 
79 static zfetch_stats_t zfetch_stats = {
80 	{ "hits",			KSTAT_DATA_UINT64 },
81 	{ "misses",			KSTAT_DATA_UINT64 },
82 	{ "colinear_hits",		KSTAT_DATA_UINT64 },
83 	{ "colinear_misses",		KSTAT_DATA_UINT64 },
84 	{ "stride_hits",		KSTAT_DATA_UINT64 },
85 	{ "stride_misses",		KSTAT_DATA_UINT64 },
86 	{ "reclaim_successes",		KSTAT_DATA_UINT64 },
87 	{ "reclaim_failures",		KSTAT_DATA_UINT64 },
88 	{ "streams_resets",		KSTAT_DATA_UINT64 },
89 	{ "streams_noresets",		KSTAT_DATA_UINT64 },
90 	{ "bogus_streams",		KSTAT_DATA_UINT64 },
91 };
92 
93 #define	ZFETCHSTAT_INCR(stat, val) \
94 	atomic_add_64(&zfetch_stats.stat.value.ui64, (val));
95 
96 #define	ZFETCHSTAT_BUMP(stat)		ZFETCHSTAT_INCR(stat, 1);
97 
98 kstat_t		*zfetch_ksp;
99 
100 /*
101  * Given a zfetch structure and a zstream structure, determine whether the
102  * blocks to be read are part of a co-linear pair of existing prefetch
103  * streams.  If a set is found, coalesce the streams, removing one, and
104  * configure the prefetch so it looks for a strided access pattern.
105  *
106  * In other words: if we find two sequential access streams that are
107  * the same length and distance N appart, and this read is N from the
108  * last stream, then we are probably in a strided access pattern.  So
109  * combine the two sequential streams into a single strided stream.
110  *
111  * Returns whether co-linear streams were found.
112  */
113 static boolean_t
dmu_zfetch_colinear(zfetch_t * zf,zstream_t * zh)114 dmu_zfetch_colinear(zfetch_t *zf, zstream_t *zh)
115 {
116 	zstream_t	*z_walk;
117 	zstream_t	*z_comp;
118 
119 	if (! rw_tryenter(&zf->zf_rwlock, RW_WRITER))
120 		return (0);
121 
122 	if (zh == NULL) {
123 		rw_exit(&zf->zf_rwlock);
124 		return (0);
125 	}
126 
127 	for (z_walk = list_head(&zf->zf_stream); z_walk;
128 	    z_walk = list_next(&zf->zf_stream, z_walk)) {
129 		for (z_comp = list_next(&zf->zf_stream, z_walk); z_comp;
130 		    z_comp = list_next(&zf->zf_stream, z_comp)) {
131 			int64_t		diff;
132 
133 			if (z_walk->zst_len != z_walk->zst_stride ||
134 			    z_comp->zst_len != z_comp->zst_stride) {
135 				continue;
136 			}
137 
138 			diff = z_comp->zst_offset - z_walk->zst_offset;
139 			if (z_comp->zst_offset + diff == zh->zst_offset) {
140 				z_walk->zst_offset = zh->zst_offset;
141 				z_walk->zst_direction = diff < 0 ? -1 : 1;
142 				z_walk->zst_stride =
143 				    diff * z_walk->zst_direction;
144 				z_walk->zst_ph_offset =
145 				    zh->zst_offset + z_walk->zst_stride;
146 				dmu_zfetch_stream_remove(zf, z_comp);
147 				mutex_destroy(&z_comp->zst_lock);
148 				kmem_free(z_comp, sizeof (zstream_t));
149 
150 				dmu_zfetch_dofetch(zf, z_walk);
151 
152 				rw_exit(&zf->zf_rwlock);
153 				return (1);
154 			}
155 
156 			diff = z_walk->zst_offset - z_comp->zst_offset;
157 			if (z_walk->zst_offset + diff == zh->zst_offset) {
158 				z_walk->zst_offset = zh->zst_offset;
159 				z_walk->zst_direction = diff < 0 ? -1 : 1;
160 				z_walk->zst_stride =
161 				    diff * z_walk->zst_direction;
162 				z_walk->zst_ph_offset =
163 				    zh->zst_offset + z_walk->zst_stride;
164 				dmu_zfetch_stream_remove(zf, z_comp);
165 				mutex_destroy(&z_comp->zst_lock);
166 				kmem_free(z_comp, sizeof (zstream_t));
167 
168 				dmu_zfetch_dofetch(zf, z_walk);
169 
170 				rw_exit(&zf->zf_rwlock);
171 				return (1);
172 			}
173 		}
174 	}
175 
176 	rw_exit(&zf->zf_rwlock);
177 	return (0);
178 }
179 
180 /*
181  * Given a zstream_t, determine the bounds of the prefetch.  Then call the
182  * routine that actually prefetches the individual blocks.
183  */
184 static void
dmu_zfetch_dofetch(zfetch_t * zf,zstream_t * zs)185 dmu_zfetch_dofetch(zfetch_t *zf, zstream_t *zs)
186 {
187 	uint64_t	prefetch_tail;
188 	uint64_t	prefetch_limit;
189 	uint64_t	prefetch_ofst;
190 	uint64_t	prefetch_len;
191 	uint64_t	blocks_fetched;
192 
193 	zs->zst_stride = MAX((int64_t)zs->zst_stride, zs->zst_len);
194 	zs->zst_cap = MIN(zfetch_block_cap, 2 * zs->zst_cap);
195 
196 	prefetch_tail = MAX((int64_t)zs->zst_ph_offset,
197 	    (int64_t)(zs->zst_offset + zs->zst_stride));
198 	/*
199 	 * XXX: use a faster division method?
200 	 */
201 	prefetch_limit = zs->zst_offset + zs->zst_len +
202 	    (zs->zst_cap * zs->zst_stride) / zs->zst_len;
203 
204 	while (prefetch_tail < prefetch_limit) {
205 		prefetch_ofst = zs->zst_offset + zs->zst_direction *
206 		    (prefetch_tail - zs->zst_offset);
207 
208 		prefetch_len = zs->zst_len;
209 
210 		/*
211 		 * Don't prefetch beyond the end of the file, if working
212 		 * backwards.
213 		 */
214 		if ((zs->zst_direction == ZFETCH_BACKWARD) &&
215 		    (prefetch_ofst > prefetch_tail)) {
216 			prefetch_len += prefetch_ofst;
217 			prefetch_ofst = 0;
218 		}
219 
220 		/* don't prefetch more than we're supposed to */
221 		if (prefetch_len > zs->zst_len)
222 			break;
223 
224 		blocks_fetched = dmu_zfetch_fetch(zf->zf_dnode,
225 		    prefetch_ofst, zs->zst_len);
226 
227 		prefetch_tail += zs->zst_stride;
228 		/* stop if we've run out of stuff to prefetch */
229 		if (blocks_fetched < zs->zst_len)
230 			break;
231 	}
232 	zs->zst_ph_offset = prefetch_tail;
233 	zs->zst_last = ddi_get_lbolt();
234 }
235 
236 void
zfetch_init(void)237 zfetch_init(void)
238 {
239 
240 	zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc",
241 	    KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t),
242 	    KSTAT_FLAG_VIRTUAL);
243 
244 	if (zfetch_ksp != NULL) {
245 		zfetch_ksp->ks_data = &zfetch_stats;
246 		kstat_install(zfetch_ksp);
247 	}
248 }
249 
250 void
zfetch_fini(void)251 zfetch_fini(void)
252 {
253 	if (zfetch_ksp != NULL) {
254 		kstat_delete(zfetch_ksp);
255 		zfetch_ksp = NULL;
256 	}
257 }
258 
259 /*
260  * This takes a pointer to a zfetch structure and a dnode.  It performs the
261  * necessary setup for the zfetch structure, grokking data from the
262  * associated dnode.
263  */
264 void
dmu_zfetch_init(zfetch_t * zf,dnode_t * dno)265 dmu_zfetch_init(zfetch_t *zf, dnode_t *dno)
266 {
267 	if (zf == NULL) {
268 		return;
269 	}
270 
271 	zf->zf_dnode = dno;
272 	zf->zf_stream_cnt = 0;
273 	zf->zf_alloc_fail = 0;
274 
275 	list_create(&zf->zf_stream, sizeof (zstream_t),
276 	    offsetof(zstream_t, zst_node));
277 
278 	rw_init(&zf->zf_rwlock, NULL, RW_DEFAULT, NULL);
279 }
280 
281 /*
282  * This function computes the actual size, in blocks, that can be prefetched,
283  * and fetches it.
284  */
285 static uint64_t
dmu_zfetch_fetch(dnode_t * dn,uint64_t blkid,uint64_t nblks)286 dmu_zfetch_fetch(dnode_t *dn, uint64_t blkid, uint64_t nblks)
287 {
288 	uint64_t	fetchsz;
289 	uint64_t	i;
290 
291 	fetchsz = dmu_zfetch_fetchsz(dn, blkid, nblks);
292 
293 	for (i = 0; i < fetchsz; i++) {
294 		dbuf_prefetch(dn, 0, blkid + i, ZIO_PRIORITY_ASYNC_READ,
295 		    ARC_FLAG_PREFETCH);
296 	}
297 
298 	return (fetchsz);
299 }
300 
301 /*
302  * this function returns the number of blocks that would be prefetched, based
303  * upon the supplied dnode, blockid, and nblks.  This is used so that we can
304  * update streams in place, and then prefetch with their old value after the
305  * fact.  This way, we can delay the prefetch, but subsequent accesses to the
306  * stream won't result in the same data being prefetched multiple times.
307  */
308 static uint64_t
dmu_zfetch_fetchsz(dnode_t * dn,uint64_t blkid,uint64_t nblks)309 dmu_zfetch_fetchsz(dnode_t *dn, uint64_t blkid, uint64_t nblks)
310 {
311 	uint64_t	fetchsz;
312 
313 	if (blkid > dn->dn_maxblkid) {
314 		return (0);
315 	}
316 
317 	/* compute fetch size */
318 	if (blkid + nblks + 1 > dn->dn_maxblkid) {
319 		fetchsz = (dn->dn_maxblkid - blkid) + 1;
320 		ASSERT(blkid + fetchsz - 1 <= dn->dn_maxblkid);
321 	} else {
322 		fetchsz = nblks;
323 	}
324 
325 
326 	return (fetchsz);
327 }
328 
329 /*
330  * given a zfetch and a zstream structure, see if there is an associated zstream
331  * for this block read.  If so, it starts a prefetch for the stream it
332  * located and returns true, otherwise it returns false
333  */
334 static boolean_t
dmu_zfetch_find(zfetch_t * zf,zstream_t * zh,int prefetched)335 dmu_zfetch_find(zfetch_t *zf, zstream_t *zh, int prefetched)
336 {
337 	zstream_t	*zs;
338 	int64_t		diff;
339 	int		reset = !prefetched;
340 	int		rc = 0;
341 
342 	if (zh == NULL)
343 		return (0);
344 
345 	/*
346 	 * XXX: This locking strategy is a bit coarse; however, it's impact has
347 	 * yet to be tested.  If this turns out to be an issue, it can be
348 	 * modified in a number of different ways.
349 	 */
350 
351 	rw_enter(&zf->zf_rwlock, RW_READER);
352 top:
353 
354 	for (zs = list_head(&zf->zf_stream); zs;
355 	    zs = list_next(&zf->zf_stream, zs)) {
356 
357 		/*
358 		 * XXX - should this be an assert?
359 		 */
360 		if (zs->zst_len == 0) {
361 			/* bogus stream */
362 			ZFETCHSTAT_BUMP(zfetchstat_bogus_streams);
363 			continue;
364 		}
365 
366 		/*
367 		 * We hit this case when we are in a strided prefetch stream:
368 		 * we will read "len" blocks before "striding".
369 		 */
370 		if (zh->zst_offset >= zs->zst_offset &&
371 		    zh->zst_offset < zs->zst_offset + zs->zst_len) {
372 			if (prefetched) {
373 				/* already fetched */
374 				ZFETCHSTAT_BUMP(zfetchstat_stride_hits);
375 				rc = 1;
376 				goto out;
377 			} else {
378 				ZFETCHSTAT_BUMP(zfetchstat_stride_misses);
379 			}
380 		}
381 
382 		/*
383 		 * This is the forward sequential read case: we increment
384 		 * len by one each time we hit here, so we will enter this
385 		 * case on every read.
386 		 */
387 		if (zh->zst_offset == zs->zst_offset + zs->zst_len) {
388 
389 			reset = !prefetched && zs->zst_len > 1;
390 
391 			mutex_enter(&zs->zst_lock);
392 
393 			if (zh->zst_offset != zs->zst_offset + zs->zst_len) {
394 				mutex_exit(&zs->zst_lock);
395 				goto top;
396 			}
397 			zs->zst_len += zh->zst_len;
398 			diff = zs->zst_len - zfetch_block_cap;
399 			if (diff > 0) {
400 				zs->zst_offset += diff;
401 				zs->zst_len = zs->zst_len > diff ?
402 				    zs->zst_len - diff : 0;
403 			}
404 			zs->zst_direction = ZFETCH_FORWARD;
405 
406 			break;
407 
408 		/*
409 		 * Same as above, but reading backwards through the file.
410 		 */
411 		} else if (zh->zst_offset == zs->zst_offset - zh->zst_len) {
412 			/* backwards sequential access */
413 
414 			reset = !prefetched && zs->zst_len > 1;
415 
416 			mutex_enter(&zs->zst_lock);
417 
418 			if (zh->zst_offset != zs->zst_offset - zh->zst_len) {
419 				mutex_exit(&zs->zst_lock);
420 				goto top;
421 			}
422 
423 			zs->zst_offset = zs->zst_offset > zh->zst_len ?
424 			    zs->zst_offset - zh->zst_len : 0;
425 			zs->zst_ph_offset = zs->zst_ph_offset > zh->zst_len ?
426 			    zs->zst_ph_offset - zh->zst_len : 0;
427 			zs->zst_len += zh->zst_len;
428 
429 			diff = zs->zst_len - zfetch_block_cap;
430 			if (diff > 0) {
431 				zs->zst_ph_offset = zs->zst_ph_offset > diff ?
432 				    zs->zst_ph_offset - diff : 0;
433 				zs->zst_len = zs->zst_len > diff ?
434 				    zs->zst_len - diff : zs->zst_len;
435 			}
436 			zs->zst_direction = ZFETCH_BACKWARD;
437 
438 			break;
439 
440 		} else if ((zh->zst_offset - zs->zst_offset - zs->zst_stride <
441 		    zs->zst_len) && (zs->zst_len != zs->zst_stride)) {
442 			/* strided forward access */
443 
444 			mutex_enter(&zs->zst_lock);
445 
446 			if ((zh->zst_offset - zs->zst_offset - zs->zst_stride >=
447 			    zs->zst_len) || (zs->zst_len == zs->zst_stride)) {
448 				mutex_exit(&zs->zst_lock);
449 				goto top;
450 			}
451 
452 			zs->zst_offset += zs->zst_stride;
453 			zs->zst_direction = ZFETCH_FORWARD;
454 
455 			break;
456 
457 		} else if ((zh->zst_offset - zs->zst_offset + zs->zst_stride <
458 		    zs->zst_len) && (zs->zst_len != zs->zst_stride)) {
459 			/* strided reverse access */
460 
461 			mutex_enter(&zs->zst_lock);
462 
463 			if ((zh->zst_offset - zs->zst_offset + zs->zst_stride >=
464 			    zs->zst_len) || (zs->zst_len == zs->zst_stride)) {
465 				mutex_exit(&zs->zst_lock);
466 				goto top;
467 			}
468 
469 			zs->zst_offset = zs->zst_offset > zs->zst_stride ?
470 			    zs->zst_offset - zs->zst_stride : 0;
471 			zs->zst_ph_offset = (zs->zst_ph_offset >
472 			    (2 * zs->zst_stride)) ?
473 			    (zs->zst_ph_offset - (2 * zs->zst_stride)) : 0;
474 			zs->zst_direction = ZFETCH_BACKWARD;
475 
476 			break;
477 		}
478 	}
479 
480 	if (zs) {
481 		if (reset) {
482 			zstream_t *remove = zs;
483 
484 			ZFETCHSTAT_BUMP(zfetchstat_stream_resets);
485 			rc = 0;
486 			mutex_exit(&zs->zst_lock);
487 			rw_exit(&zf->zf_rwlock);
488 			rw_enter(&zf->zf_rwlock, RW_WRITER);
489 			/*
490 			 * Relocate the stream, in case someone removes
491 			 * it while we were acquiring the WRITER lock.
492 			 */
493 			for (zs = list_head(&zf->zf_stream); zs;
494 			    zs = list_next(&zf->zf_stream, zs)) {
495 				if (zs == remove) {
496 					dmu_zfetch_stream_remove(zf, zs);
497 					mutex_destroy(&zs->zst_lock);
498 					kmem_free(zs, sizeof (zstream_t));
499 					break;
500 				}
501 			}
502 		} else {
503 			ZFETCHSTAT_BUMP(zfetchstat_stream_noresets);
504 			rc = 1;
505 			dmu_zfetch_dofetch(zf, zs);
506 			mutex_exit(&zs->zst_lock);
507 		}
508 	}
509 out:
510 	rw_exit(&zf->zf_rwlock);
511 	return (rc);
512 }
513 
514 /*
515  * Clean-up state associated with a zfetch structure.  This frees allocated
516  * structure members, empties the zf_stream tree, and generally makes things
517  * nice.  This doesn't free the zfetch_t itself, that's left to the caller.
518  */
519 void
dmu_zfetch_rele(zfetch_t * zf)520 dmu_zfetch_rele(zfetch_t *zf)
521 {
522 	zstream_t	*zs;
523 	zstream_t	*zs_next;
524 
525 	ASSERT(!RW_LOCK_HELD(&zf->zf_rwlock));
526 
527 	for (zs = list_head(&zf->zf_stream); zs; zs = zs_next) {
528 		zs_next = list_next(&zf->zf_stream, zs);
529 
530 		list_remove(&zf->zf_stream, zs);
531 		mutex_destroy(&zs->zst_lock);
532 		kmem_free(zs, sizeof (zstream_t));
533 	}
534 	list_destroy(&zf->zf_stream);
535 	rw_destroy(&zf->zf_rwlock);
536 
537 	zf->zf_dnode = NULL;
538 }
539 
540 /*
541  * Given a zfetch and zstream structure, insert the zstream structure into the
542  * AVL tree contained within the zfetch structure.  Peform the appropriate
543  * book-keeping.  It is possible that another thread has inserted a stream which
544  * matches one that we are about to insert, so we must be sure to check for this
545  * case.  If one is found, return failure, and let the caller cleanup the
546  * duplicates.
547  */
548 static int
dmu_zfetch_stream_insert(zfetch_t * zf,zstream_t * zs)549 dmu_zfetch_stream_insert(zfetch_t *zf, zstream_t *zs)
550 {
551 	zstream_t	*zs_walk;
552 	zstream_t	*zs_next;
553 
554 	ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
555 
556 	for (zs_walk = list_head(&zf->zf_stream); zs_walk; zs_walk = zs_next) {
557 		zs_next = list_next(&zf->zf_stream, zs_walk);
558 
559 		if (dmu_zfetch_streams_equal(zs_walk, zs)) {
560 			return (0);
561 		}
562 	}
563 
564 	list_insert_head(&zf->zf_stream, zs);
565 	zf->zf_stream_cnt++;
566 	return (1);
567 }
568 
569 
570 /*
571  * Walk the list of zstreams in the given zfetch, find an old one (by time), and
572  * reclaim it for use by the caller.
573  */
574 static zstream_t *
dmu_zfetch_stream_reclaim(zfetch_t * zf)575 dmu_zfetch_stream_reclaim(zfetch_t *zf)
576 {
577 	zstream_t	*zs;
578 
579 	if (! rw_tryenter(&zf->zf_rwlock, RW_WRITER))
580 		return (0);
581 
582 	for (zs = list_head(&zf->zf_stream); zs;
583 	    zs = list_next(&zf->zf_stream, zs)) {
584 
585 		if (((ddi_get_lbolt() - zs->zst_last)/hz) > zfetch_min_sec_reap)
586 			break;
587 	}
588 
589 	if (zs) {
590 		dmu_zfetch_stream_remove(zf, zs);
591 		mutex_destroy(&zs->zst_lock);
592 		bzero(zs, sizeof (zstream_t));
593 	} else {
594 		zf->zf_alloc_fail++;
595 	}
596 	rw_exit(&zf->zf_rwlock);
597 
598 	return (zs);
599 }
600 
601 /*
602  * Given a zfetch and zstream structure, remove the zstream structure from its
603  * container in the zfetch structure.  Perform the appropriate book-keeping.
604  */
605 static void
dmu_zfetch_stream_remove(zfetch_t * zf,zstream_t * zs)606 dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs)
607 {
608 	ASSERT(RW_WRITE_HELD(&zf->zf_rwlock));
609 
610 	list_remove(&zf->zf_stream, zs);
611 	zf->zf_stream_cnt--;
612 }
613 
614 static int
dmu_zfetch_streams_equal(zstream_t * zs1,zstream_t * zs2)615 dmu_zfetch_streams_equal(zstream_t *zs1, zstream_t *zs2)
616 {
617 	if (zs1->zst_offset != zs2->zst_offset)
618 		return (0);
619 
620 	if (zs1->zst_len != zs2->zst_len)
621 		return (0);
622 
623 	if (zs1->zst_stride != zs2->zst_stride)
624 		return (0);
625 
626 	if (zs1->zst_ph_offset != zs2->zst_ph_offset)
627 		return (0);
628 
629 	if (zs1->zst_cap != zs2->zst_cap)
630 		return (0);
631 
632 	if (zs1->zst_direction != zs2->zst_direction)
633 		return (0);
634 
635 	return (1);
636 }
637 
638 /*
639  * This is the prefetch entry point.  It calls all of the other dmu_zfetch
640  * routines to create, delete, find, or operate upon prefetch streams.
641  */
642 void
dmu_zfetch(zfetch_t * zf,uint64_t offset,uint64_t size,int prefetched)643 dmu_zfetch(zfetch_t *zf, uint64_t offset, uint64_t size, int prefetched)
644 {
645 	zstream_t	zst;
646 	zstream_t	*newstream;
647 	boolean_t	fetched;
648 	int		inserted;
649 	unsigned int	blkshft;
650 	uint64_t	blksz;
651 
652 	if (zfs_prefetch_disable)
653 		return;
654 
655 	/* files that aren't ln2 blocksz are only one block -- nothing to do */
656 	if (!zf->zf_dnode->dn_datablkshift)
657 		return;
658 
659 	/* convert offset and size, into blockid and nblocks */
660 	blkshft = zf->zf_dnode->dn_datablkshift;
661 	blksz = (1 << blkshft);
662 
663 	bzero(&zst, sizeof (zstream_t));
664 	zst.zst_offset = offset >> blkshft;
665 	zst.zst_len = (P2ROUNDUP(offset + size, blksz) -
666 	    P2ALIGN(offset, blksz)) >> blkshft;
667 
668 	fetched = dmu_zfetch_find(zf, &zst, prefetched);
669 	if (fetched) {
670 		ZFETCHSTAT_BUMP(zfetchstat_hits);
671 	} else {
672 		ZFETCHSTAT_BUMP(zfetchstat_misses);
673 		fetched = dmu_zfetch_colinear(zf, &zst);
674 		if (fetched) {
675 			ZFETCHSTAT_BUMP(zfetchstat_colinear_hits);
676 		} else {
677 			ZFETCHSTAT_BUMP(zfetchstat_colinear_misses);
678 		}
679 	}
680 
681 	if (!fetched) {
682 		newstream = dmu_zfetch_stream_reclaim(zf);
683 
684 		/*
685 		 * we still couldn't find a stream, drop the lock, and allocate
686 		 * one if possible.  Otherwise, give up and go home.
687 		 */
688 		if (newstream) {
689 			ZFETCHSTAT_BUMP(zfetchstat_reclaim_successes);
690 		} else {
691 			uint64_t	maxblocks;
692 			uint32_t	max_streams;
693 			uint32_t	cur_streams;
694 
695 			ZFETCHSTAT_BUMP(zfetchstat_reclaim_failures);
696 			cur_streams = zf->zf_stream_cnt;
697 			maxblocks = zf->zf_dnode->dn_maxblkid;
698 
699 			max_streams = MIN(zfetch_max_streams,
700 			    (maxblocks / zfetch_block_cap));
701 			if (max_streams == 0) {
702 				max_streams++;
703 			}
704 
705 			if (cur_streams >= max_streams) {
706 				return;
707 			}
708 			newstream = kmem_zalloc(sizeof (zstream_t), KM_SLEEP);
709 		}
710 
711 		newstream->zst_offset = zst.zst_offset;
712 		newstream->zst_len = zst.zst_len;
713 		newstream->zst_stride = zst.zst_len;
714 		newstream->zst_ph_offset = zst.zst_len + zst.zst_offset;
715 		newstream->zst_cap = zst.zst_len;
716 		newstream->zst_direction = ZFETCH_FORWARD;
717 		newstream->zst_last = ddi_get_lbolt();
718 
719 		mutex_init(&newstream->zst_lock, NULL, MUTEX_DEFAULT, NULL);
720 
721 		rw_enter(&zf->zf_rwlock, RW_WRITER);
722 		inserted = dmu_zfetch_stream_insert(zf, newstream);
723 		rw_exit(&zf->zf_rwlock);
724 
725 		if (!inserted) {
726 			mutex_destroy(&newstream->zst_lock);
727 			kmem_free(newstream, sizeof (zstream_t));
728 		}
729 	}
730 }
731