2 * This file and its contents are supplied under the terms of the
3 * Common Development and Distribution License ("CDDL"), version 1.0.
4 * You may only use this file in accordance with the terms of version
7 * A full copy of the text of the CDDL should have accompanied this
8 * source. A copy of the CDDL is also available via the Internet at
9 * http://www.illumos.org/license/CDDL.
13 * Copyright (c) 2014 by Chunwei Chen. All rights reserved.
14 * Copyright (c) 2016 by Delphix. All rights reserved.
18 * See abd.c for a general overview of the arc buffered data (ABD).
20 * Using a large proportion of scattered ABDs decreases ARC fragmentation since
21 * when we are at the limit of allocatable space, using equal-size chunks will
22 * allow us to quickly reclaim enough space for a new large allocation (assuming
23 * it is also scattered).
25 * ABDs are allocated scattered by default unless the caller uses
26 * abd_alloc_linear() or zfs_abd_scatter_enabled is disabled.
29 #include <sys/abd_impl.h>
30 #include <sys/param.h>
31 #include <sys/types.h>
33 #include <sys/zfs_context.h>
34 #include <sys/zfs_znode.h>
36 typedef struct abd_stats {
37 kstat_named_t abdstat_struct_size;
38 kstat_named_t abdstat_scatter_cnt;
39 kstat_named_t abdstat_scatter_data_size;
40 kstat_named_t abdstat_scatter_chunk_waste;
41 kstat_named_t abdstat_linear_cnt;
42 kstat_named_t abdstat_linear_data_size;
45 static abd_stats_t abd_stats = {
46 /* Amount of memory occupied by all of the abd_t struct allocations */
47 { "struct_size", KSTAT_DATA_UINT64 },
49 * The number of scatter ABDs which are currently allocated, excluding
50 * ABDs which don't own their data (for instance the ones which were
51 * allocated through abd_get_offset()).
53 { "scatter_cnt", KSTAT_DATA_UINT64 },
54 /* Amount of data stored in all scatter ABDs tracked by scatter_cnt */
55 { "scatter_data_size", KSTAT_DATA_UINT64 },
57 * The amount of space wasted at the end of the last chunk across all
58 * scatter ABDs tracked by scatter_cnt.
60 { "scatter_chunk_waste", KSTAT_DATA_UINT64 },
62 * The number of linear ABDs which are currently allocated, excluding
63 * ABDs which don't own their data (for instance the ones which were
64 * allocated through abd_get_offset() and abd_get_from_buf()). If an
65 * ABD takes ownership of its buf then it will become tracked.
67 { "linear_cnt", KSTAT_DATA_UINT64 },
68 /* Amount of data stored in all linear ABDs tracked by linear_cnt */
69 { "linear_data_size", KSTAT_DATA_UINT64 },
73 wmsum_t abdstat_struct_size;
74 wmsum_t abdstat_scatter_cnt;
75 wmsum_t abdstat_scatter_data_size;
76 wmsum_t abdstat_scatter_chunk_waste;
77 wmsum_t abdstat_linear_cnt;
78 wmsum_t abdstat_linear_data_size;
82 * The size of the chunks ABD allocates. Because the sizes allocated from the
83 * kmem_cache can't change, this tunable can only be modified at boot. Changing
84 * it at runtime would cause ABD iteration to work incorrectly for ABDs which
85 * were allocated with the old size, so a safeguard has been put in place which
86 * will cause the machine to panic if you change it and try to access the data
87 * within a scattered ABD.
89 size_t zfs_abd_chunk_size = 4096;
92 SYSCTL_DECL(_vfs_zfs);
94 SYSCTL_INT(_vfs_zfs, OID_AUTO, abd_scatter_enabled, CTLFLAG_RWTUN,
95 &zfs_abd_scatter_enabled, 0, "Enable scattered ARC data buffers");
96 SYSCTL_ULONG(_vfs_zfs, OID_AUTO, abd_chunk_size, CTLFLAG_RDTUN,
97 &zfs_abd_chunk_size, 0, "The size of the chunks ABD allocates");
100 kmem_cache_t *abd_chunk_cache;
101 static kstat_t *abd_ksp;
104 * We use a scattered SPA_MAXBLOCKSIZE sized ABD whose chunks are
105 * just a single zero'd sized zfs_abd_chunk_size buffer. This
106 * allows us to conserve memory by only using a single zero buffer
107 * for the scatter chunks.
109 abd_t *abd_zero_scatter = NULL;
110 static char *abd_zero_buf = NULL;
113 abd_free_chunk(void *c)
115 kmem_cache_free(abd_chunk_cache, c);
119 abd_chunkcnt_for_bytes(size_t size)
121 return (P2ROUNDUP(size, zfs_abd_chunk_size) / zfs_abd_chunk_size);
125 abd_scatter_chunkcnt(abd_t *abd)
127 ASSERT(!abd_is_linear(abd));
128 return (abd_chunkcnt_for_bytes(
129 ABD_SCATTER(abd).abd_offset + abd->abd_size));
133 abd_size_alloc_linear(size_t size)
135 return (size <= zfs_abd_chunk_size ? B_TRUE : B_FALSE);
139 abd_update_scatter_stats(abd_t *abd, abd_stats_op_t op)
141 uint_t n = abd_scatter_chunkcnt(abd);
142 ASSERT(op == ABDSTAT_INCR || op == ABDSTAT_DECR);
143 int waste = n * zfs_abd_chunk_size - abd->abd_size;
144 if (op == ABDSTAT_INCR) {
145 ABDSTAT_BUMP(abdstat_scatter_cnt);
146 ABDSTAT_INCR(abdstat_scatter_data_size, abd->abd_size);
147 ABDSTAT_INCR(abdstat_scatter_chunk_waste, waste);
148 arc_space_consume(waste, ARC_SPACE_ABD_CHUNK_WASTE);
150 ABDSTAT_BUMPDOWN(abdstat_scatter_cnt);
151 ABDSTAT_INCR(abdstat_scatter_data_size, -(int)abd->abd_size);
152 ABDSTAT_INCR(abdstat_scatter_chunk_waste, -waste);
153 arc_space_return(waste, ARC_SPACE_ABD_CHUNK_WASTE);
158 abd_update_linear_stats(abd_t *abd, abd_stats_op_t op)
160 ASSERT(op == ABDSTAT_INCR || op == ABDSTAT_DECR);
161 if (op == ABDSTAT_INCR) {
162 ABDSTAT_BUMP(abdstat_linear_cnt);
163 ABDSTAT_INCR(abdstat_linear_data_size, abd->abd_size);
165 ABDSTAT_BUMPDOWN(abdstat_linear_cnt);
166 ABDSTAT_INCR(abdstat_linear_data_size, -(int)abd->abd_size);
171 abd_verify_scatter(abd_t *abd)
176 * There is no scatter linear pages in FreeBSD so there is an
177 * if an error if the ABD has been marked as a linear page.
179 ASSERT(!abd_is_linear_page(abd));
180 ASSERT3U(ABD_SCATTER(abd).abd_offset, <,
182 n = abd_scatter_chunkcnt(abd);
183 for (i = 0; i < n; i++) {
184 ASSERT3P(ABD_SCATTER(abd).abd_chunks[i], !=, NULL);
189 abd_alloc_chunks(abd_t *abd, size_t size)
193 n = abd_chunkcnt_for_bytes(size);
194 for (i = 0; i < n; i++) {
195 void *c = kmem_cache_alloc(abd_chunk_cache, KM_PUSHPAGE);
196 ASSERT3P(c, !=, NULL);
197 ABD_SCATTER(abd).abd_chunks[i] = c;
199 ABD_SCATTER(abd).abd_chunk_size = zfs_abd_chunk_size;
203 abd_free_chunks(abd_t *abd)
207 n = abd_scatter_chunkcnt(abd);
208 for (i = 0; i < n; i++) {
209 abd_free_chunk(ABD_SCATTER(abd).abd_chunks[i]);
214 abd_alloc_struct_impl(size_t size)
216 uint_t chunkcnt = abd_chunkcnt_for_bytes(size);
218 * In the event we are allocating a gang ABD, the size passed in
219 * will be 0. We must make sure to set abd_size to the size of an
220 * ABD struct as opposed to an ABD scatter with 0 chunks. The gang
221 * ABD struct allocation accounts for an additional 24 bytes over
222 * a scatter ABD with 0 chunks.
224 size_t abd_size = MAX(sizeof (abd_t),
225 offsetof(abd_t, abd_u.abd_scatter.abd_chunks[chunkcnt]));
226 abd_t *abd = kmem_alloc(abd_size, KM_PUSHPAGE);
227 ASSERT3P(abd, !=, NULL);
228 ABDSTAT_INCR(abdstat_struct_size, abd_size);
234 abd_free_struct_impl(abd_t *abd)
236 uint_t chunkcnt = abd_is_linear(abd) || abd_is_gang(abd) ? 0 :
237 abd_scatter_chunkcnt(abd);
238 ssize_t size = MAX(sizeof (abd_t),
239 offsetof(abd_t, abd_u.abd_scatter.abd_chunks[chunkcnt]));
240 kmem_free(abd, size);
241 ABDSTAT_INCR(abdstat_struct_size, -size);
245 * Allocate scatter ABD of size SPA_MAXBLOCKSIZE, where
246 * each chunk in the scatterlist will be set to abd_zero_buf.
249 abd_alloc_zero_scatter(void)
253 n = abd_chunkcnt_for_bytes(SPA_MAXBLOCKSIZE);
254 abd_zero_buf = kmem_zalloc(zfs_abd_chunk_size, KM_SLEEP);
255 abd_zero_scatter = abd_alloc_struct(SPA_MAXBLOCKSIZE);
257 abd_zero_scatter->abd_flags |= ABD_FLAG_OWNER | ABD_FLAG_ZEROS;
258 abd_zero_scatter->abd_size = SPA_MAXBLOCKSIZE;
260 ABD_SCATTER(abd_zero_scatter).abd_offset = 0;
261 ABD_SCATTER(abd_zero_scatter).abd_chunk_size =
264 for (i = 0; i < n; i++) {
265 ABD_SCATTER(abd_zero_scatter).abd_chunks[i] =
269 ABDSTAT_BUMP(abdstat_scatter_cnt);
270 ABDSTAT_INCR(abdstat_scatter_data_size, zfs_abd_chunk_size);
274 abd_free_zero_scatter(void)
276 ABDSTAT_BUMPDOWN(abdstat_scatter_cnt);
277 ABDSTAT_INCR(abdstat_scatter_data_size, -(int)zfs_abd_chunk_size);
279 abd_free_struct(abd_zero_scatter);
280 abd_zero_scatter = NULL;
281 kmem_free(abd_zero_buf, zfs_abd_chunk_size);
285 abd_kstats_update(kstat_t *ksp, int rw)
287 abd_stats_t *as = ksp->ks_data;
289 if (rw == KSTAT_WRITE)
291 as->abdstat_struct_size.value.ui64 =
292 wmsum_value(&abd_sums.abdstat_struct_size);
293 as->abdstat_scatter_cnt.value.ui64 =
294 wmsum_value(&abd_sums.abdstat_scatter_cnt);
295 as->abdstat_scatter_data_size.value.ui64 =
296 wmsum_value(&abd_sums.abdstat_scatter_data_size);
297 as->abdstat_scatter_chunk_waste.value.ui64 =
298 wmsum_value(&abd_sums.abdstat_scatter_chunk_waste);
299 as->abdstat_linear_cnt.value.ui64 =
300 wmsum_value(&abd_sums.abdstat_linear_cnt);
301 as->abdstat_linear_data_size.value.ui64 =
302 wmsum_value(&abd_sums.abdstat_linear_data_size);
309 abd_chunk_cache = kmem_cache_create("abd_chunk", zfs_abd_chunk_size, 0,
310 NULL, NULL, NULL, NULL, 0, KMC_NODEBUG);
312 wmsum_init(&abd_sums.abdstat_struct_size, 0);
313 wmsum_init(&abd_sums.abdstat_scatter_cnt, 0);
314 wmsum_init(&abd_sums.abdstat_scatter_data_size, 0);
315 wmsum_init(&abd_sums.abdstat_scatter_chunk_waste, 0);
316 wmsum_init(&abd_sums.abdstat_linear_cnt, 0);
317 wmsum_init(&abd_sums.abdstat_linear_data_size, 0);
319 abd_ksp = kstat_create("zfs", 0, "abdstats", "misc", KSTAT_TYPE_NAMED,
320 sizeof (abd_stats) / sizeof (kstat_named_t), KSTAT_FLAG_VIRTUAL);
321 if (abd_ksp != NULL) {
322 abd_ksp->ks_data = &abd_stats;
323 abd_ksp->ks_update = abd_kstats_update;
324 kstat_install(abd_ksp);
327 abd_alloc_zero_scatter();
333 abd_free_zero_scatter();
335 if (abd_ksp != NULL) {
336 kstat_delete(abd_ksp);
340 wmsum_fini(&abd_sums.abdstat_struct_size);
341 wmsum_fini(&abd_sums.abdstat_scatter_cnt);
342 wmsum_fini(&abd_sums.abdstat_scatter_data_size);
343 wmsum_fini(&abd_sums.abdstat_scatter_chunk_waste);
344 wmsum_fini(&abd_sums.abdstat_linear_cnt);
345 wmsum_fini(&abd_sums.abdstat_linear_data_size);
347 kmem_cache_destroy(abd_chunk_cache);
348 abd_chunk_cache = NULL;
352 abd_free_linear_page(abd_t *abd)
355 * FreeBSD does not have scatter linear pages
356 * so there is an error.
362 * If we're going to use this ABD for doing I/O using the block layer, the
363 * consumer of the ABD data doesn't care if it's scattered or not, and we don't
364 * plan to store this ABD in memory for a long period of time, we should
365 * allocate the ABD type that requires the least data copying to do the I/O.
367 * Currently this is linear ABDs, however if ldi_strategy() can ever issue I/Os
368 * using a scatter/gather list we should switch to that and replace this call
369 * with vanilla abd_alloc().
372 abd_alloc_for_io(size_t size, boolean_t is_metadata)
374 return (abd_alloc_linear(size, is_metadata));
378 abd_get_offset_scatter(abd_t *abd, abd_t *sabd, size_t off)
381 ASSERT3U(off, <=, sabd->abd_size);
383 size_t new_offset = ABD_SCATTER(sabd).abd_offset + off;
384 uint_t chunkcnt = abd_scatter_chunkcnt(sabd) -
385 (new_offset / zfs_abd_chunk_size);
388 * If an abd struct is provided, it is only the minimum size. If we
389 * need additional chunks, we need to allocate a new struct.
392 offsetof(abd_t, abd_u.abd_scatter.abd_chunks[chunkcnt]) >
398 abd = abd_alloc_struct(chunkcnt * zfs_abd_chunk_size);
401 * Even if this buf is filesystem metadata, we only track that
402 * if we own the underlying data buffer, which is not true in
403 * this case. Therefore, we don't ever use ABD_FLAG_META here.
406 ABD_SCATTER(abd).abd_offset = new_offset % zfs_abd_chunk_size;
407 ABD_SCATTER(abd).abd_chunk_size = zfs_abd_chunk_size;
409 /* Copy the scatterlist starting at the correct offset */
410 (void) memcpy(&ABD_SCATTER(abd).abd_chunks,
411 &ABD_SCATTER(sabd).abd_chunks[new_offset /
413 chunkcnt * sizeof (void *));
419 abd_iter_scatter_chunk_offset(struct abd_iter *aiter)
421 ASSERT(!abd_is_linear(aiter->iter_abd));
422 return ((ABD_SCATTER(aiter->iter_abd).abd_offset +
423 aiter->iter_pos) % zfs_abd_chunk_size);
427 abd_iter_scatter_chunk_index(struct abd_iter *aiter)
429 ASSERT(!abd_is_linear(aiter->iter_abd));
430 return ((ABD_SCATTER(aiter->iter_abd).abd_offset +
431 aiter->iter_pos) / zfs_abd_chunk_size);
435 * Initialize the abd_iter.
438 abd_iter_init(struct abd_iter *aiter, abd_t *abd)
440 ASSERT(!abd_is_gang(abd));
442 aiter->iter_abd = abd;
444 aiter->iter_mapaddr = NULL;
445 aiter->iter_mapsize = 0;
449 * This is just a helper function to see if we have exhausted the
450 * abd_iter and reached the end.
453 abd_iter_at_end(struct abd_iter *aiter)
455 return (aiter->iter_pos == aiter->iter_abd->abd_size);
459 * Advance the iterator by a certain amount. Cannot be called when a chunk is
460 * in use. This can be safely called when the aiter has already exhausted, in
461 * which case this does nothing.
464 abd_iter_advance(struct abd_iter *aiter, size_t amount)
466 ASSERT3P(aiter->iter_mapaddr, ==, NULL);
467 ASSERT0(aiter->iter_mapsize);
469 /* There's nothing left to advance to, so do nothing */
470 if (abd_iter_at_end(aiter))
473 aiter->iter_pos += amount;
477 * Map the current chunk into aiter. This can be safely called when the aiter
478 * has already exhausted, in which case this does nothing.
481 abd_iter_map(struct abd_iter *aiter)
486 ASSERT3P(aiter->iter_mapaddr, ==, NULL);
487 ASSERT0(aiter->iter_mapsize);
489 /* Panic if someone has changed zfs_abd_chunk_size */
490 IMPLY(!abd_is_linear(aiter->iter_abd), zfs_abd_chunk_size ==
491 ABD_SCATTER(aiter->iter_abd).abd_chunk_size);
493 /* There's nothing left to iterate over, so do nothing */
494 if (abd_iter_at_end(aiter))
497 if (abd_is_linear(aiter->iter_abd)) {
498 offset = aiter->iter_pos;
499 aiter->iter_mapsize = aiter->iter_abd->abd_size - offset;
500 paddr = ABD_LINEAR_BUF(aiter->iter_abd);
502 size_t index = abd_iter_scatter_chunk_index(aiter);
503 offset = abd_iter_scatter_chunk_offset(aiter);
504 aiter->iter_mapsize = MIN(zfs_abd_chunk_size - offset,
505 aiter->iter_abd->abd_size - aiter->iter_pos);
506 paddr = ABD_SCATTER(aiter->iter_abd).abd_chunks[index];
508 aiter->iter_mapaddr = (char *)paddr + offset;
512 * Unmap the current chunk from aiter. This can be safely called when the aiter
513 * has already exhausted, in which case this does nothing.
516 abd_iter_unmap(struct abd_iter *aiter)
518 /* There's nothing left to unmap, so do nothing */
519 if (abd_iter_at_end(aiter))
522 ASSERT3P(aiter->iter_mapaddr, !=, NULL);
523 ASSERT3U(aiter->iter_mapsize, >, 0);
525 aiter->iter_mapaddr = NULL;
526 aiter->iter_mapsize = 0;
530 abd_cache_reap_now(void)
532 kmem_cache_reap_soon(abd_chunk_cache);