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 * Copyright (c) 2013, 2017 by Delphix. All rights reserved.
27 */
28
29#include <sys/zfs_context.h>
30#include <sys/spa.h>
31#include <sys/vdev_impl.h>
32#include <sys/zio.h>
33#include <sys/kstat.h>
34#include <sys/abd.h>
35
36/*
37 * Virtual device read-ahead caching.
38 *
39 * This file implements a simple LRU read-ahead cache.  When the DMU reads
40 * a given block, it will often want other, nearby blocks soon thereafter.
41 * We take advantage of this by reading a larger disk region and caching
42 * the result.  In the best case, this can turn 128 back-to-back 512-byte
43 * reads into a single 64k read followed by 127 cache hits; this reduces
44 * latency dramatically.  In the worst case, it can turn an isolated 512-byte
45 * read into a 64k read, which doesn't affect latency all that much but is
46 * terribly wasteful of bandwidth.  A more intelligent version of the cache
47 * could keep track of access patterns and not do read-ahead unless it sees
48 * at least two temporally close I/Os to the same region.  Currently, only
49 * metadata I/O is inflated.  A futher enhancement could take advantage of
50 * more semantic information about the I/O.  And it could use something
51 * faster than an AVL tree; that was chosen solely for convenience.
52 *
53 * There are five cache operations: allocate, fill, read, write, evict.
54 *
55 * (1) Allocate.  This reserves a cache entry for the specified region.
56 *     We separate the allocate and fill operations so that multiple threads
57 *     don't generate I/O for the same cache miss.
58 *
59 * (2) Fill.  When the I/O for a cache miss completes, the fill routine
60 *     places the data in the previously allocated cache entry.
61 *
62 * (3) Read.  Read data from the cache.
63 *
64 * (4) Write.  Update cache contents after write completion.
65 *
66 * (5) Evict.  When allocating a new entry, we evict the oldest (LRU) entry
67 *     if the total cache size exceeds zfs_vdev_cache_size.
68 */
69
70/*
71 * These tunables are for performance analysis.
72 */
73/*
74 * All i/os smaller than zfs_vdev_cache_max will be turned into
75 * 1<<zfs_vdev_cache_bshift byte reads by the vdev_cache (aka software
76 * track buffer).  At most zfs_vdev_cache_size bytes will be kept in each
77 * vdev's vdev_cache.
78 *
79 * TODO: Note that with the current ZFS code, it turns out that the
80 * vdev cache is not helpful, and in some cases actually harmful.  It
81 * is better if we disable this.  Once some time has passed, we should
82 * actually remove this to simplify the code.  For now we just disable
83 * it by setting the zfs_vdev_cache_size to zero.  Note that Solaris 11
84 * has made these same changes.
85 */
86int zfs_vdev_cache_max = 1<<14;			/* 16KB */
87int zfs_vdev_cache_size = 0;
88int zfs_vdev_cache_bshift = 16;
89
90#define	VCBS (1 << zfs_vdev_cache_bshift)	/* 64KB */
91
92kstat_t	*vdc_ksp = NULL;
93
94typedef struct vdc_stats {
95	kstat_named_t vdc_stat_delegations;
96	kstat_named_t vdc_stat_hits;
97	kstat_named_t vdc_stat_misses;
98} vdc_stats_t;
99
100static vdc_stats_t vdc_stats = {
101	{ "delegations",	KSTAT_DATA_UINT64 },
102	{ "hits",		KSTAT_DATA_UINT64 },
103	{ "misses",		KSTAT_DATA_UINT64 }
104};
105
106#define	VDCSTAT_BUMP(stat)	atomic_inc_64(&vdc_stats.stat.value.ui64);
107
108static inline int
109vdev_cache_offset_compare(const void *a1, const void *a2)
110{
111	const vdev_cache_entry_t *ve1 = (const vdev_cache_entry_t *)a1;
112	const vdev_cache_entry_t *ve2 = (const vdev_cache_entry_t *)a2;
113
114	return (AVL_CMP(ve1->ve_offset, ve2->ve_offset));
115}
116
117static int
118vdev_cache_lastused_compare(const void *a1, const void *a2)
119{
120	const vdev_cache_entry_t *ve1 = (const vdev_cache_entry_t *)a1;
121	const vdev_cache_entry_t *ve2 = (const vdev_cache_entry_t *)a2;
122
123	int cmp = AVL_CMP(ve1->ve_lastused, ve2->ve_lastused);
124	if (likely(cmp))
125		return (cmp);
126
127	/*
128	 * Among equally old entries, sort by offset to ensure uniqueness.
129	 */
130	return (vdev_cache_offset_compare(a1, a2));
131}
132
133/*
134 * Evict the specified entry from the cache.
135 */
136static void
137vdev_cache_evict(vdev_cache_t *vc, vdev_cache_entry_t *ve)
138{
139	ASSERT(MUTEX_HELD(&vc->vc_lock));
140	ASSERT3P(ve->ve_fill_io, ==, NULL);
141	ASSERT3P(ve->ve_abd, !=, NULL);
142
143	avl_remove(&vc->vc_lastused_tree, ve);
144	avl_remove(&vc->vc_offset_tree, ve);
145	abd_free(ve->ve_abd);
146	kmem_free(ve, sizeof (vdev_cache_entry_t));
147}
148
149/*
150 * Allocate an entry in the cache.  At the point we don't have the data,
151 * we're just creating a placeholder so that multiple threads don't all
152 * go off and read the same blocks.
153 */
154static vdev_cache_entry_t *
155vdev_cache_allocate(zio_t *zio)
156{
157	vdev_cache_t *vc = &zio->io_vd->vdev_cache;
158	uint64_t offset = P2ALIGN(zio->io_offset, VCBS);
159	vdev_cache_entry_t *ve;
160
161	ASSERT(MUTEX_HELD(&vc->vc_lock));
162
163	if (zfs_vdev_cache_size == 0)
164		return (NULL);
165
166	/*
167	 * If adding a new entry would exceed the cache size,
168	 * evict the oldest entry (LRU).
169	 */
170	if ((avl_numnodes(&vc->vc_lastused_tree) << zfs_vdev_cache_bshift) >
171	    zfs_vdev_cache_size) {
172		ve = avl_first(&vc->vc_lastused_tree);
173		if (ve->ve_fill_io != NULL)
174			return (NULL);
175		ASSERT3U(ve->ve_hits, !=, 0);
176		vdev_cache_evict(vc, ve);
177	}
178
179	ve = kmem_zalloc(sizeof (vdev_cache_entry_t), KM_SLEEP);
180	ve->ve_offset = offset;
181	ve->ve_lastused = ddi_get_lbolt();
182	ve->ve_abd = abd_alloc_for_io(VCBS, B_TRUE);
183
184	avl_add(&vc->vc_offset_tree, ve);
185	avl_add(&vc->vc_lastused_tree, ve);
186
187	return (ve);
188}
189
190static void
191vdev_cache_hit(vdev_cache_t *vc, vdev_cache_entry_t *ve, zio_t *zio)
192{
193	uint64_t cache_phase = P2PHASE(zio->io_offset, VCBS);
194
195	ASSERT(MUTEX_HELD(&vc->vc_lock));
196	ASSERT3P(ve->ve_fill_io, ==, NULL);
197
198	if (ve->ve_lastused != ddi_get_lbolt()) {
199		avl_remove(&vc->vc_lastused_tree, ve);
200		ve->ve_lastused = ddi_get_lbolt();
201		avl_add(&vc->vc_lastused_tree, ve);
202	}
203
204	ve->ve_hits++;
205	abd_copy_off(zio->io_abd, ve->ve_abd, 0, cache_phase, zio->io_size);
206}
207
208/*
209 * Fill a previously allocated cache entry with data.
210 */
211static void
212vdev_cache_fill(zio_t *fio)
213{
214	vdev_t *vd = fio->io_vd;
215	vdev_cache_t *vc = &vd->vdev_cache;
216	vdev_cache_entry_t *ve = fio->io_private;
217	zio_t *pio;
218
219	ASSERT3U(fio->io_size, ==, VCBS);
220
221	/*
222	 * Add data to the cache.
223	 */
224	mutex_enter(&vc->vc_lock);
225
226	ASSERT3P(ve->ve_fill_io, ==, fio);
227	ASSERT3U(ve->ve_offset, ==, fio->io_offset);
228	ASSERT3P(ve->ve_abd, ==, fio->io_abd);
229
230	ve->ve_fill_io = NULL;
231
232	/*
233	 * Even if this cache line was invalidated by a missed write update,
234	 * any reads that were queued up before the missed update are still
235	 * valid, so we can satisfy them from this line before we evict it.
236	 */
237	zio_link_t *zl = NULL;
238	while ((pio = zio_walk_parents(fio, &zl)) != NULL)
239		vdev_cache_hit(vc, ve, pio);
240
241	if (fio->io_error || ve->ve_missed_update)
242		vdev_cache_evict(vc, ve);
243
244	mutex_exit(&vc->vc_lock);
245}
246
247/*
248 * Read data from the cache.  Returns B_TRUE cache hit, B_FALSE on miss.
249 */
250boolean_t
251vdev_cache_read(zio_t *zio)
252{
253	vdev_cache_t *vc = &zio->io_vd->vdev_cache;
254	vdev_cache_entry_t *ve, ve_search;
255	uint64_t cache_offset = P2ALIGN(zio->io_offset, VCBS);
256	uint64_t cache_phase = P2PHASE(zio->io_offset, VCBS);
257	zio_t *fio;
258
259	ASSERT3U(zio->io_type, ==, ZIO_TYPE_READ);
260
261	if (zio->io_flags & ZIO_FLAG_DONT_CACHE)
262		return (B_FALSE);
263
264	if (zio->io_size > zfs_vdev_cache_max)
265		return (B_FALSE);
266
267	/*
268	 * If the I/O straddles two or more cache blocks, don't cache it.
269	 */
270	if (P2BOUNDARY(zio->io_offset, zio->io_size, VCBS))
271		return (B_FALSE);
272
273	ASSERT3U(cache_phase + zio->io_size, <=, VCBS);
274
275	mutex_enter(&vc->vc_lock);
276
277	ve_search.ve_offset = cache_offset;
278	ve = avl_find(&vc->vc_offset_tree, &ve_search, NULL);
279
280	if (ve != NULL) {
281		if (ve->ve_missed_update) {
282			mutex_exit(&vc->vc_lock);
283			return (B_FALSE);
284		}
285
286		if ((fio = ve->ve_fill_io) != NULL) {
287			zio_vdev_io_bypass(zio);
288			zio_add_child(zio, fio);
289			mutex_exit(&vc->vc_lock);
290			VDCSTAT_BUMP(vdc_stat_delegations);
291			return (B_TRUE);
292		}
293
294		vdev_cache_hit(vc, ve, zio);
295		zio_vdev_io_bypass(zio);
296
297		mutex_exit(&vc->vc_lock);
298		VDCSTAT_BUMP(vdc_stat_hits);
299		return (B_TRUE);
300	}
301
302	ve = vdev_cache_allocate(zio);
303
304	if (ve == NULL) {
305		mutex_exit(&vc->vc_lock);
306		return (B_FALSE);
307	}
308
309	fio = zio_vdev_delegated_io(zio->io_vd, cache_offset,
310	    ve->ve_abd, VCBS, ZIO_TYPE_READ, ZIO_PRIORITY_NOW,
311	    ZIO_FLAG_DONT_CACHE, vdev_cache_fill, ve);
312
313	ve->ve_fill_io = fio;
314	zio_vdev_io_bypass(zio);
315	zio_add_child(zio, fio);
316
317	mutex_exit(&vc->vc_lock);
318	zio_nowait(fio);
319	VDCSTAT_BUMP(vdc_stat_misses);
320
321	return (B_TRUE);
322}
323
324/*
325 * Update cache contents upon write completion.
326 */
327void
328vdev_cache_write(zio_t *zio)
329{
330	vdev_cache_t *vc = &zio->io_vd->vdev_cache;
331	vdev_cache_entry_t *ve, ve_search;
332	uint64_t io_start = zio->io_offset;
333	uint64_t io_end = io_start + zio->io_size;
334	uint64_t min_offset = P2ALIGN(io_start, VCBS);
335	uint64_t max_offset = P2ROUNDUP(io_end, VCBS);
336	avl_index_t where;
337
338	ASSERT3U(zio->io_type, ==, ZIO_TYPE_WRITE);
339
340	mutex_enter(&vc->vc_lock);
341
342	ve_search.ve_offset = min_offset;
343	ve = avl_find(&vc->vc_offset_tree, &ve_search, &where);
344
345	if (ve == NULL)
346		ve = avl_nearest(&vc->vc_offset_tree, where, AVL_AFTER);
347
348	while (ve != NULL && ve->ve_offset < max_offset) {
349		uint64_t start = MAX(ve->ve_offset, io_start);
350		uint64_t end = MIN(ve->ve_offset + VCBS, io_end);
351
352		if (ve->ve_fill_io != NULL) {
353			ve->ve_missed_update = 1;
354		} else {
355			abd_copy_off(ve->ve_abd, zio->io_abd,
356			    start - ve->ve_offset, start - io_start,
357			    end - start);
358		}
359		ve = AVL_NEXT(&vc->vc_offset_tree, ve);
360	}
361	mutex_exit(&vc->vc_lock);
362}
363
364void
365vdev_cache_purge(vdev_t *vd)
366{
367	vdev_cache_t *vc = &vd->vdev_cache;
368	vdev_cache_entry_t *ve;
369
370	mutex_enter(&vc->vc_lock);
371	while ((ve = avl_first(&vc->vc_offset_tree)) != NULL)
372		vdev_cache_evict(vc, ve);
373	mutex_exit(&vc->vc_lock);
374}
375
376void
377vdev_cache_init(vdev_t *vd)
378{
379	vdev_cache_t *vc = &vd->vdev_cache;
380
381	mutex_init(&vc->vc_lock, NULL, MUTEX_DEFAULT, NULL);
382
383	avl_create(&vc->vc_offset_tree, vdev_cache_offset_compare,
384	    sizeof (vdev_cache_entry_t),
385	    offsetof(struct vdev_cache_entry, ve_offset_node));
386
387	avl_create(&vc->vc_lastused_tree, vdev_cache_lastused_compare,
388	    sizeof (vdev_cache_entry_t),
389	    offsetof(struct vdev_cache_entry, ve_lastused_node));
390}
391
392void
393vdev_cache_fini(vdev_t *vd)
394{
395	vdev_cache_t *vc = &vd->vdev_cache;
396
397	vdev_cache_purge(vd);
398
399	avl_destroy(&vc->vc_offset_tree);
400	avl_destroy(&vc->vc_lastused_tree);
401
402	mutex_destroy(&vc->vc_lock);
403}
404
405void
406vdev_cache_stat_init(void)
407{
408	vdc_ksp = kstat_create("zfs", 0, "vdev_cache_stats", "misc",
409	    KSTAT_TYPE_NAMED, sizeof (vdc_stats) / sizeof (kstat_named_t),
410	    KSTAT_FLAG_VIRTUAL);
411	if (vdc_ksp != NULL) {
412		vdc_ksp->ks_data = &vdc_stats;
413		kstat_install(vdc_ksp);
414	}
415}
416
417void
418vdev_cache_stat_fini(void)
419{
420	if (vdc_ksp != NULL) {
421		kstat_delete(vdc_ksp);
422		vdc_ksp = NULL;
423	}
424}
425