2 * Copyright (C) 2008 Oracle. All rights reserved.
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public
6 * License v2 as published by the Free Software Foundation.
8 * This program is distributed in the hope that it will be useful,
9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
11 * General Public License for more details.
13 * You should have received a copy of the GNU General Public
14 * License along with this program; if not, write to the
15 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
16 * Boston, MA 021110-1307, USA.
19 #include <linux/kernel.h>
20 #include <linux/bio.h>
21 #include <linux/buffer_head.h>
22 #include <linux/file.h>
24 #include <linux/pagemap.h>
25 #include <linux/highmem.h>
26 #include <linux/time.h>
27 #include <linux/init.h>
28 #include <linux/string.h>
29 #include <linux/backing-dev.h>
30 #include <linux/mpage.h>
31 #include <linux/swap.h>
32 #include <linux/writeback.h>
33 #include <linux/bit_spinlock.h>
34 #include <linux/slab.h>
35 #include <linux/sched/mm.h>
36 #include <linux/sort.h>
37 #include <linux/log2.h>
40 #include "transaction.h"
41 #include "btrfs_inode.h"
43 #include "ordered-data.h"
44 #include "compression.h"
45 #include "extent_io.h"
46 #include "extent_map.h"
48 static int btrfs_decompress_bio(struct compressed_bio *cb);
50 static inline int compressed_bio_size(struct btrfs_fs_info *fs_info,
51 unsigned long disk_size)
53 u16 csum_size = btrfs_super_csum_size(fs_info->super_copy);
55 return sizeof(struct compressed_bio) +
56 (DIV_ROUND_UP(disk_size, fs_info->sectorsize)) * csum_size;
59 static int check_compressed_csum(struct btrfs_inode *inode,
60 struct compressed_bio *cb,
68 u32 *cb_sum = &cb->sums;
70 if (inode->flags & BTRFS_INODE_NODATASUM)
73 for (i = 0; i < cb->nr_pages; i++) {
74 page = cb->compressed_pages[i];
77 kaddr = kmap_atomic(page);
78 csum = btrfs_csum_data(kaddr, csum, PAGE_SIZE);
79 btrfs_csum_final(csum, (u8 *)&csum);
82 if (csum != *cb_sum) {
83 btrfs_print_data_csum_error(inode, disk_start, csum,
84 *cb_sum, cb->mirror_num);
96 /* when we finish reading compressed pages from the disk, we
97 * decompress them and then run the bio end_io routines on the
98 * decompressed pages (in the inode address space).
100 * This allows the checksumming and other IO error handling routines
103 * The compressed pages are freed here, and it must be run
106 static void end_compressed_bio_read(struct bio *bio)
108 struct compressed_bio *cb = bio->bi_private;
112 unsigned int mirror = btrfs_io_bio(bio)->mirror_num;
118 /* if there are more bios still pending for this compressed
121 if (!refcount_dec_and_test(&cb->pending_bios))
125 * Record the correct mirror_num in cb->orig_bio so that
126 * read-repair can work properly.
128 ASSERT(btrfs_io_bio(cb->orig_bio));
129 btrfs_io_bio(cb->orig_bio)->mirror_num = mirror;
130 cb->mirror_num = mirror;
133 * Some IO in this cb have failed, just skip checksum as there
134 * is no way it could be correct.
140 ret = check_compressed_csum(BTRFS_I(inode), cb,
141 (u64)bio->bi_iter.bi_sector << 9);
145 /* ok, we're the last bio for this extent, lets start
148 ret = btrfs_decompress_bio(cb);
154 /* release the compressed pages */
156 for (index = 0; index < cb->nr_pages; index++) {
157 page = cb->compressed_pages[index];
158 page->mapping = NULL;
162 /* do io completion on the original bio */
164 bio_io_error(cb->orig_bio);
167 struct bio_vec *bvec;
170 * we have verified the checksum already, set page
171 * checked so the end_io handlers know about it
173 ASSERT(!bio_flagged(bio, BIO_CLONED));
174 bio_for_each_segment_all(bvec, cb->orig_bio, i)
175 SetPageChecked(bvec->bv_page);
177 bio_endio(cb->orig_bio);
180 /* finally free the cb struct */
181 kfree(cb->compressed_pages);
188 * Clear the writeback bits on all of the file
189 * pages for a compressed write
191 static noinline void end_compressed_writeback(struct inode *inode,
192 const struct compressed_bio *cb)
194 unsigned long index = cb->start >> PAGE_SHIFT;
195 unsigned long end_index = (cb->start + cb->len - 1) >> PAGE_SHIFT;
196 struct page *pages[16];
197 unsigned long nr_pages = end_index - index + 1;
202 mapping_set_error(inode->i_mapping, -EIO);
204 while (nr_pages > 0) {
205 ret = find_get_pages_contig(inode->i_mapping, index,
207 nr_pages, ARRAY_SIZE(pages)), pages);
213 for (i = 0; i < ret; i++) {
215 SetPageError(pages[i]);
216 end_page_writeback(pages[i]);
222 /* the inode may be gone now */
226 * do the cleanup once all the compressed pages hit the disk.
227 * This will clear writeback on the file pages and free the compressed
230 * This also calls the writeback end hooks for the file pages so that
231 * metadata and checksums can be updated in the file.
233 static void end_compressed_bio_write(struct bio *bio)
235 struct extent_io_tree *tree;
236 struct compressed_bio *cb = bio->bi_private;
244 /* if there are more bios still pending for this compressed
247 if (!refcount_dec_and_test(&cb->pending_bios))
250 /* ok, we're the last bio for this extent, step one is to
251 * call back into the FS and do all the end_io operations
254 tree = &BTRFS_I(inode)->io_tree;
255 cb->compressed_pages[0]->mapping = cb->inode->i_mapping;
256 tree->ops->writepage_end_io_hook(cb->compressed_pages[0],
258 cb->start + cb->len - 1,
261 BLK_STS_OK : BLK_STS_NOTSUPP);
262 cb->compressed_pages[0]->mapping = NULL;
264 end_compressed_writeback(inode, cb);
265 /* note, our inode could be gone now */
268 * release the compressed pages, these came from alloc_page and
269 * are not attached to the inode at all
272 for (index = 0; index < cb->nr_pages; index++) {
273 page = cb->compressed_pages[index];
274 page->mapping = NULL;
278 /* finally free the cb struct */
279 kfree(cb->compressed_pages);
286 * worker function to build and submit bios for previously compressed pages.
287 * The corresponding pages in the inode should be marked for writeback
288 * and the compressed pages should have a reference on them for dropping
289 * when the IO is complete.
291 * This also checksums the file bytes and gets things ready for
294 blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
295 unsigned long len, u64 disk_start,
296 unsigned long compressed_len,
297 struct page **compressed_pages,
298 unsigned long nr_pages,
299 unsigned int write_flags)
301 struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
302 struct bio *bio = NULL;
303 struct compressed_bio *cb;
304 unsigned long bytes_left;
305 struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
308 u64 first_byte = disk_start;
309 struct block_device *bdev;
311 int skip_sum = BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM;
313 WARN_ON(start & ((u64)PAGE_SIZE - 1));
314 cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS);
316 return BLK_STS_RESOURCE;
317 refcount_set(&cb->pending_bios, 0);
323 cb->compressed_pages = compressed_pages;
324 cb->compressed_len = compressed_len;
326 cb->nr_pages = nr_pages;
328 bdev = fs_info->fs_devices->latest_bdev;
330 bio = btrfs_bio_alloc(bdev, first_byte);
331 bio->bi_opf = REQ_OP_WRITE | write_flags;
332 bio->bi_private = cb;
333 bio->bi_end_io = end_compressed_bio_write;
334 refcount_set(&cb->pending_bios, 1);
336 /* create and submit bios for the compressed pages */
337 bytes_left = compressed_len;
338 for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
341 page = compressed_pages[pg_index];
342 page->mapping = inode->i_mapping;
343 if (bio->bi_iter.bi_size)
344 submit = io_tree->ops->merge_bio_hook(page, 0,
348 page->mapping = NULL;
349 if (submit || bio_add_page(bio, page, PAGE_SIZE, 0) <
354 * inc the count before we submit the bio so
355 * we know the end IO handler won't happen before
356 * we inc the count. Otherwise, the cb might get
357 * freed before we're done setting it up
359 refcount_inc(&cb->pending_bios);
360 ret = btrfs_bio_wq_end_io(fs_info, bio,
361 BTRFS_WQ_ENDIO_DATA);
362 BUG_ON(ret); /* -ENOMEM */
365 ret = btrfs_csum_one_bio(inode, bio, start, 1);
366 BUG_ON(ret); /* -ENOMEM */
369 ret = btrfs_map_bio(fs_info, bio, 0, 1);
371 bio->bi_status = ret;
377 bio = btrfs_bio_alloc(bdev, first_byte);
378 bio->bi_opf = REQ_OP_WRITE | write_flags;
379 bio->bi_private = cb;
380 bio->bi_end_io = end_compressed_bio_write;
381 bio_add_page(bio, page, PAGE_SIZE, 0);
383 if (bytes_left < PAGE_SIZE) {
385 "bytes left %lu compress len %lu nr %lu",
386 bytes_left, cb->compressed_len, cb->nr_pages);
388 bytes_left -= PAGE_SIZE;
389 first_byte += PAGE_SIZE;
394 ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA);
395 BUG_ON(ret); /* -ENOMEM */
398 ret = btrfs_csum_one_bio(inode, bio, start, 1);
399 BUG_ON(ret); /* -ENOMEM */
402 ret = btrfs_map_bio(fs_info, bio, 0, 1);
404 bio->bi_status = ret;
412 static u64 bio_end_offset(struct bio *bio)
414 struct bio_vec *last = &bio->bi_io_vec[bio->bi_vcnt - 1];
416 return page_offset(last->bv_page) + last->bv_len + last->bv_offset;
419 static noinline int add_ra_bio_pages(struct inode *inode,
421 struct compressed_bio *cb)
423 unsigned long end_index;
424 unsigned long pg_index;
426 u64 isize = i_size_read(inode);
429 unsigned long nr_pages = 0;
430 struct extent_map *em;
431 struct address_space *mapping = inode->i_mapping;
432 struct extent_map_tree *em_tree;
433 struct extent_io_tree *tree;
437 last_offset = bio_end_offset(cb->orig_bio);
438 em_tree = &BTRFS_I(inode)->extent_tree;
439 tree = &BTRFS_I(inode)->io_tree;
444 end_index = (i_size_read(inode) - 1) >> PAGE_SHIFT;
446 while (last_offset < compressed_end) {
447 pg_index = last_offset >> PAGE_SHIFT;
449 if (pg_index > end_index)
453 page = radix_tree_lookup(&mapping->page_tree, pg_index);
455 if (page && !radix_tree_exceptional_entry(page)) {
462 page = __page_cache_alloc(mapping_gfp_constraint(mapping,
467 if (add_to_page_cache_lru(page, mapping, pg_index, GFP_NOFS)) {
472 end = last_offset + PAGE_SIZE - 1;
474 * at this point, we have a locked page in the page cache
475 * for these bytes in the file. But, we have to make
476 * sure they map to this compressed extent on disk.
478 set_page_extent_mapped(page);
479 lock_extent(tree, last_offset, end);
480 read_lock(&em_tree->lock);
481 em = lookup_extent_mapping(em_tree, last_offset,
483 read_unlock(&em_tree->lock);
485 if (!em || last_offset < em->start ||
486 (last_offset + PAGE_SIZE > extent_map_end(em)) ||
487 (em->block_start >> 9) != cb->orig_bio->bi_iter.bi_sector) {
489 unlock_extent(tree, last_offset, end);
496 if (page->index == end_index) {
498 size_t zero_offset = isize & (PAGE_SIZE - 1);
502 zeros = PAGE_SIZE - zero_offset;
503 userpage = kmap_atomic(page);
504 memset(userpage + zero_offset, 0, zeros);
505 flush_dcache_page(page);
506 kunmap_atomic(userpage);
510 ret = bio_add_page(cb->orig_bio, page,
513 if (ret == PAGE_SIZE) {
517 unlock_extent(tree, last_offset, end);
523 last_offset += PAGE_SIZE;
529 * for a compressed read, the bio we get passed has all the inode pages
530 * in it. We don't actually do IO on those pages but allocate new ones
531 * to hold the compressed pages on disk.
533 * bio->bi_iter.bi_sector points to the compressed extent on disk
534 * bio->bi_io_vec points to all of the inode pages
536 * After the compressed pages are read, we copy the bytes into the
537 * bio we were passed and then call the bio end_io calls
539 blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
540 int mirror_num, unsigned long bio_flags)
542 struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
543 struct extent_io_tree *tree;
544 struct extent_map_tree *em_tree;
545 struct compressed_bio *cb;
546 unsigned long compressed_len;
547 unsigned long nr_pages;
548 unsigned long pg_index;
550 struct block_device *bdev;
551 struct bio *comp_bio;
552 u64 cur_disk_byte = (u64)bio->bi_iter.bi_sector << 9;
555 struct extent_map *em;
556 blk_status_t ret = BLK_STS_RESOURCE;
560 tree = &BTRFS_I(inode)->io_tree;
561 em_tree = &BTRFS_I(inode)->extent_tree;
563 /* we need the actual starting offset of this extent in the file */
564 read_lock(&em_tree->lock);
565 em = lookup_extent_mapping(em_tree,
566 page_offset(bio->bi_io_vec->bv_page),
568 read_unlock(&em_tree->lock);
570 return BLK_STS_IOERR;
572 compressed_len = em->block_len;
573 cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS);
577 refcount_set(&cb->pending_bios, 0);
580 cb->mirror_num = mirror_num;
583 cb->start = em->orig_start;
585 em_start = em->start;
590 cb->len = bio->bi_iter.bi_size;
591 cb->compressed_len = compressed_len;
592 cb->compress_type = extent_compress_type(bio_flags);
595 nr_pages = DIV_ROUND_UP(compressed_len, PAGE_SIZE);
596 cb->compressed_pages = kcalloc(nr_pages, sizeof(struct page *),
598 if (!cb->compressed_pages)
601 bdev = fs_info->fs_devices->latest_bdev;
603 for (pg_index = 0; pg_index < nr_pages; pg_index++) {
604 cb->compressed_pages[pg_index] = alloc_page(GFP_NOFS |
606 if (!cb->compressed_pages[pg_index]) {
607 faili = pg_index - 1;
608 ret = BLK_STS_RESOURCE;
612 faili = nr_pages - 1;
613 cb->nr_pages = nr_pages;
615 add_ra_bio_pages(inode, em_start + em_len, cb);
617 /* include any pages we added in add_ra-bio_pages */
618 cb->len = bio->bi_iter.bi_size;
620 comp_bio = btrfs_bio_alloc(bdev, cur_disk_byte);
621 bio_set_op_attrs (comp_bio, REQ_OP_READ, 0);
622 comp_bio->bi_private = cb;
623 comp_bio->bi_end_io = end_compressed_bio_read;
624 refcount_set(&cb->pending_bios, 1);
626 for (pg_index = 0; pg_index < nr_pages; pg_index++) {
629 page = cb->compressed_pages[pg_index];
630 page->mapping = inode->i_mapping;
631 page->index = em_start >> PAGE_SHIFT;
633 if (comp_bio->bi_iter.bi_size)
634 submit = tree->ops->merge_bio_hook(page, 0,
638 page->mapping = NULL;
639 if (submit || bio_add_page(comp_bio, page, PAGE_SIZE, 0) <
643 ret = btrfs_bio_wq_end_io(fs_info, comp_bio,
644 BTRFS_WQ_ENDIO_DATA);
645 BUG_ON(ret); /* -ENOMEM */
648 * inc the count before we submit the bio so
649 * we know the end IO handler won't happen before
650 * we inc the count. Otherwise, the cb might get
651 * freed before we're done setting it up
653 refcount_inc(&cb->pending_bios);
655 if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
656 ret = btrfs_lookup_bio_sums(inode, comp_bio,
658 BUG_ON(ret); /* -ENOMEM */
660 sums += DIV_ROUND_UP(comp_bio->bi_iter.bi_size,
661 fs_info->sectorsize);
663 ret = btrfs_map_bio(fs_info, comp_bio, mirror_num, 0);
665 comp_bio->bi_status = ret;
671 comp_bio = btrfs_bio_alloc(bdev, cur_disk_byte);
672 bio_set_op_attrs(comp_bio, REQ_OP_READ, 0);
673 comp_bio->bi_private = cb;
674 comp_bio->bi_end_io = end_compressed_bio_read;
676 bio_add_page(comp_bio, page, PAGE_SIZE, 0);
678 cur_disk_byte += PAGE_SIZE;
682 ret = btrfs_bio_wq_end_io(fs_info, comp_bio, BTRFS_WQ_ENDIO_DATA);
683 BUG_ON(ret); /* -ENOMEM */
685 if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
686 ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
687 BUG_ON(ret); /* -ENOMEM */
690 ret = btrfs_map_bio(fs_info, comp_bio, mirror_num, 0);
692 comp_bio->bi_status = ret;
701 __free_page(cb->compressed_pages[faili]);
705 kfree(cb->compressed_pages);
714 * Heuristic uses systematic sampling to collect data from the input data
715 * range, the logic can be tuned by the following constants:
717 * @SAMPLING_READ_SIZE - how many bytes will be copied from for each sample
718 * @SAMPLING_INTERVAL - range from which the sampled data can be collected
720 #define SAMPLING_READ_SIZE (16)
721 #define SAMPLING_INTERVAL (256)
724 * For statistical analysis of the input data we consider bytes that form a
725 * Galois Field of 256 objects. Each object has an attribute count, ie. how
726 * many times the object appeared in the sample.
728 #define BUCKET_SIZE (256)
731 * The size of the sample is based on a statistical sampling rule of thumb.
732 * The common way is to perform sampling tests as long as the number of
733 * elements in each cell is at least 5.
735 * Instead of 5, we choose 32 to obtain more accurate results.
736 * If the data contain the maximum number of symbols, which is 256, we obtain a
737 * sample size bound by 8192.
739 * For a sample of at most 8KB of data per data range: 16 consecutive bytes
740 * from up to 512 locations.
742 #define MAX_SAMPLE_SIZE (BTRFS_MAX_UNCOMPRESSED * \
743 SAMPLING_READ_SIZE / SAMPLING_INTERVAL)
749 struct heuristic_ws {
750 /* Partial copy of input data */
753 /* Buckets store counters for each byte value */
754 struct bucket_item *bucket;
755 struct list_head list;
758 static void free_heuristic_ws(struct list_head *ws)
760 struct heuristic_ws *workspace;
762 workspace = list_entry(ws, struct heuristic_ws, list);
764 kvfree(workspace->sample);
765 kfree(workspace->bucket);
769 static struct list_head *alloc_heuristic_ws(void)
771 struct heuristic_ws *ws;
773 ws = kzalloc(sizeof(*ws), GFP_KERNEL);
775 return ERR_PTR(-ENOMEM);
777 ws->sample = kvmalloc(MAX_SAMPLE_SIZE, GFP_KERNEL);
781 ws->bucket = kcalloc(BUCKET_SIZE, sizeof(*ws->bucket), GFP_KERNEL);
785 INIT_LIST_HEAD(&ws->list);
788 free_heuristic_ws(&ws->list);
789 return ERR_PTR(-ENOMEM);
792 struct workspaces_list {
793 struct list_head idle_ws;
795 /* Number of free workspaces */
797 /* Total number of allocated workspaces */
799 /* Waiters for a free workspace */
800 wait_queue_head_t ws_wait;
803 static struct workspaces_list btrfs_comp_ws[BTRFS_COMPRESS_TYPES];
805 static struct workspaces_list btrfs_heuristic_ws;
807 static const struct btrfs_compress_op * const btrfs_compress_op[] = {
808 &btrfs_zlib_compress,
810 &btrfs_zstd_compress,
813 void __init btrfs_init_compress(void)
815 struct list_head *workspace;
818 INIT_LIST_HEAD(&btrfs_heuristic_ws.idle_ws);
819 spin_lock_init(&btrfs_heuristic_ws.ws_lock);
820 atomic_set(&btrfs_heuristic_ws.total_ws, 0);
821 init_waitqueue_head(&btrfs_heuristic_ws.ws_wait);
823 workspace = alloc_heuristic_ws();
824 if (IS_ERR(workspace)) {
826 "BTRFS: cannot preallocate heuristic workspace, will try later\n");
828 atomic_set(&btrfs_heuristic_ws.total_ws, 1);
829 btrfs_heuristic_ws.free_ws = 1;
830 list_add(workspace, &btrfs_heuristic_ws.idle_ws);
833 for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
834 INIT_LIST_HEAD(&btrfs_comp_ws[i].idle_ws);
835 spin_lock_init(&btrfs_comp_ws[i].ws_lock);
836 atomic_set(&btrfs_comp_ws[i].total_ws, 0);
837 init_waitqueue_head(&btrfs_comp_ws[i].ws_wait);
840 * Preallocate one workspace for each compression type so
841 * we can guarantee forward progress in the worst case
843 workspace = btrfs_compress_op[i]->alloc_workspace();
844 if (IS_ERR(workspace)) {
845 pr_warn("BTRFS: cannot preallocate compression workspace, will try later\n");
847 atomic_set(&btrfs_comp_ws[i].total_ws, 1);
848 btrfs_comp_ws[i].free_ws = 1;
849 list_add(workspace, &btrfs_comp_ws[i].idle_ws);
855 * This finds an available workspace or allocates a new one.
856 * If it's not possible to allocate a new one, waits until there's one.
857 * Preallocation makes a forward progress guarantees and we do not return
860 static struct list_head *__find_workspace(int type, bool heuristic)
862 struct list_head *workspace;
863 int cpus = num_online_cpus();
866 struct list_head *idle_ws;
869 wait_queue_head_t *ws_wait;
873 idle_ws = &btrfs_heuristic_ws.idle_ws;
874 ws_lock = &btrfs_heuristic_ws.ws_lock;
875 total_ws = &btrfs_heuristic_ws.total_ws;
876 ws_wait = &btrfs_heuristic_ws.ws_wait;
877 free_ws = &btrfs_heuristic_ws.free_ws;
879 idle_ws = &btrfs_comp_ws[idx].idle_ws;
880 ws_lock = &btrfs_comp_ws[idx].ws_lock;
881 total_ws = &btrfs_comp_ws[idx].total_ws;
882 ws_wait = &btrfs_comp_ws[idx].ws_wait;
883 free_ws = &btrfs_comp_ws[idx].free_ws;
888 if (!list_empty(idle_ws)) {
889 workspace = idle_ws->next;
892 spin_unlock(ws_lock);
896 if (atomic_read(total_ws) > cpus) {
899 spin_unlock(ws_lock);
900 prepare_to_wait(ws_wait, &wait, TASK_UNINTERRUPTIBLE);
901 if (atomic_read(total_ws) > cpus && !*free_ws)
903 finish_wait(ws_wait, &wait);
906 atomic_inc(total_ws);
907 spin_unlock(ws_lock);
910 * Allocation helpers call vmalloc that can't use GFP_NOFS, so we have
911 * to turn it off here because we might get called from the restricted
912 * context of btrfs_compress_bio/btrfs_compress_pages
914 nofs_flag = memalloc_nofs_save();
916 workspace = alloc_heuristic_ws();
918 workspace = btrfs_compress_op[idx]->alloc_workspace();
919 memalloc_nofs_restore(nofs_flag);
921 if (IS_ERR(workspace)) {
922 atomic_dec(total_ws);
926 * Do not return the error but go back to waiting. There's a
927 * workspace preallocated for each type and the compression
928 * time is bounded so we get to a workspace eventually. This
929 * makes our caller's life easier.
931 * To prevent silent and low-probability deadlocks (when the
932 * initial preallocation fails), check if there are any
935 if (atomic_read(total_ws) == 0) {
936 static DEFINE_RATELIMIT_STATE(_rs,
937 /* once per minute */ 60 * HZ,
940 if (__ratelimit(&_rs)) {
941 pr_warn("BTRFS: no compression workspaces, low memory, retrying\n");
949 static struct list_head *find_workspace(int type)
951 return __find_workspace(type, false);
955 * put a workspace struct back on the list or free it if we have enough
956 * idle ones sitting around
958 static void __free_workspace(int type, struct list_head *workspace,
962 struct list_head *idle_ws;
965 wait_queue_head_t *ws_wait;
969 idle_ws = &btrfs_heuristic_ws.idle_ws;
970 ws_lock = &btrfs_heuristic_ws.ws_lock;
971 total_ws = &btrfs_heuristic_ws.total_ws;
972 ws_wait = &btrfs_heuristic_ws.ws_wait;
973 free_ws = &btrfs_heuristic_ws.free_ws;
975 idle_ws = &btrfs_comp_ws[idx].idle_ws;
976 ws_lock = &btrfs_comp_ws[idx].ws_lock;
977 total_ws = &btrfs_comp_ws[idx].total_ws;
978 ws_wait = &btrfs_comp_ws[idx].ws_wait;
979 free_ws = &btrfs_comp_ws[idx].free_ws;
983 if (*free_ws <= num_online_cpus()) {
984 list_add(workspace, idle_ws);
986 spin_unlock(ws_lock);
989 spin_unlock(ws_lock);
992 free_heuristic_ws(workspace);
994 btrfs_compress_op[idx]->free_workspace(workspace);
995 atomic_dec(total_ws);
998 * Make sure counter is updated before we wake up waiters.
1001 if (waitqueue_active(ws_wait))
1005 static void free_workspace(int type, struct list_head *ws)
1007 return __free_workspace(type, ws, false);
1011 * cleanup function for module exit
1013 static void free_workspaces(void)
1015 struct list_head *workspace;
1018 while (!list_empty(&btrfs_heuristic_ws.idle_ws)) {
1019 workspace = btrfs_heuristic_ws.idle_ws.next;
1020 list_del(workspace);
1021 free_heuristic_ws(workspace);
1022 atomic_dec(&btrfs_heuristic_ws.total_ws);
1025 for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
1026 while (!list_empty(&btrfs_comp_ws[i].idle_ws)) {
1027 workspace = btrfs_comp_ws[i].idle_ws.next;
1028 list_del(workspace);
1029 btrfs_compress_op[i]->free_workspace(workspace);
1030 atomic_dec(&btrfs_comp_ws[i].total_ws);
1036 * Given an address space and start and length, compress the bytes into @pages
1037 * that are allocated on demand.
1039 * @type_level is encoded algorithm and level, where level 0 means whatever
1040 * default the algorithm chooses and is opaque here;
1041 * - compression algo are 0-3
1042 * - the level are bits 4-7
1044 * @out_pages is an in/out parameter, holds maximum number of pages to allocate
1045 * and returns number of actually allocated pages
1047 * @total_in is used to return the number of bytes actually read. It
1048 * may be smaller than the input length if we had to exit early because we
1049 * ran out of room in the pages array or because we cross the
1050 * max_out threshold.
1052 * @total_out is an in/out parameter, must be set to the input length and will
1053 * be also used to return the total number of compressed bytes
1055 * @max_out tells us the max number of bytes that we're allowed to
1058 int btrfs_compress_pages(unsigned int type_level, struct address_space *mapping,
1059 u64 start, struct page **pages,
1060 unsigned long *out_pages,
1061 unsigned long *total_in,
1062 unsigned long *total_out)
1064 struct list_head *workspace;
1066 int type = type_level & 0xF;
1068 workspace = find_workspace(type);
1070 btrfs_compress_op[type - 1]->set_level(workspace, type_level);
1071 ret = btrfs_compress_op[type-1]->compress_pages(workspace, mapping,
1074 total_in, total_out);
1075 free_workspace(type, workspace);
1080 * pages_in is an array of pages with compressed data.
1082 * disk_start is the starting logical offset of this array in the file
1084 * orig_bio contains the pages from the file that we want to decompress into
1086 * srclen is the number of bytes in pages_in
1088 * The basic idea is that we have a bio that was created by readpages.
1089 * The pages in the bio are for the uncompressed data, and they may not
1090 * be contiguous. They all correspond to the range of bytes covered by
1091 * the compressed extent.
1093 static int btrfs_decompress_bio(struct compressed_bio *cb)
1095 struct list_head *workspace;
1097 int type = cb->compress_type;
1099 workspace = find_workspace(type);
1100 ret = btrfs_compress_op[type - 1]->decompress_bio(workspace, cb);
1101 free_workspace(type, workspace);
1107 * a less complex decompression routine. Our compressed data fits in a
1108 * single page, and we want to read a single page out of it.
1109 * start_byte tells us the offset into the compressed data we're interested in
1111 int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page,
1112 unsigned long start_byte, size_t srclen, size_t destlen)
1114 struct list_head *workspace;
1117 workspace = find_workspace(type);
1119 ret = btrfs_compress_op[type-1]->decompress(workspace, data_in,
1120 dest_page, start_byte,
1123 free_workspace(type, workspace);
1127 void btrfs_exit_compress(void)
1133 * Copy uncompressed data from working buffer to pages.
1135 * buf_start is the byte offset we're of the start of our workspace buffer.
1137 * total_out is the last byte of the buffer
1139 int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start,
1140 unsigned long total_out, u64 disk_start,
1143 unsigned long buf_offset;
1144 unsigned long current_buf_start;
1145 unsigned long start_byte;
1146 unsigned long prev_start_byte;
1147 unsigned long working_bytes = total_out - buf_start;
1148 unsigned long bytes;
1150 struct bio_vec bvec = bio_iter_iovec(bio, bio->bi_iter);
1153 * start byte is the first byte of the page we're currently
1154 * copying into relative to the start of the compressed data.
1156 start_byte = page_offset(bvec.bv_page) - disk_start;
1158 /* we haven't yet hit data corresponding to this page */
1159 if (total_out <= start_byte)
1163 * the start of the data we care about is offset into
1164 * the middle of our working buffer
1166 if (total_out > start_byte && buf_start < start_byte) {
1167 buf_offset = start_byte - buf_start;
1168 working_bytes -= buf_offset;
1172 current_buf_start = buf_start;
1174 /* copy bytes from the working buffer into the pages */
1175 while (working_bytes > 0) {
1176 bytes = min_t(unsigned long, bvec.bv_len,
1177 PAGE_SIZE - buf_offset);
1178 bytes = min(bytes, working_bytes);
1180 kaddr = kmap_atomic(bvec.bv_page);
1181 memcpy(kaddr + bvec.bv_offset, buf + buf_offset, bytes);
1182 kunmap_atomic(kaddr);
1183 flush_dcache_page(bvec.bv_page);
1185 buf_offset += bytes;
1186 working_bytes -= bytes;
1187 current_buf_start += bytes;
1189 /* check if we need to pick another page */
1190 bio_advance(bio, bytes);
1191 if (!bio->bi_iter.bi_size)
1193 bvec = bio_iter_iovec(bio, bio->bi_iter);
1194 prev_start_byte = start_byte;
1195 start_byte = page_offset(bvec.bv_page) - disk_start;
1198 * We need to make sure we're only adjusting
1199 * our offset into compression working buffer when
1200 * we're switching pages. Otherwise we can incorrectly
1201 * keep copying when we were actually done.
1203 if (start_byte != prev_start_byte) {
1205 * make sure our new page is covered by this
1208 if (total_out <= start_byte)
1212 * the next page in the biovec might not be adjacent
1213 * to the last page, but it might still be found
1214 * inside this working buffer. bump our offset pointer
1216 if (total_out > start_byte &&
1217 current_buf_start < start_byte) {
1218 buf_offset = start_byte - buf_start;
1219 working_bytes = total_out - start_byte;
1220 current_buf_start = buf_start + buf_offset;
1229 * Shannon Entropy calculation
1231 * Pure byte distribution analysis fails to determine compressiability of data.
1232 * Try calculating entropy to estimate the average minimum number of bits
1233 * needed to encode the sampled data.
1235 * For convenience, return the percentage of needed bits, instead of amount of
1238 * @ENTROPY_LVL_ACEPTABLE - below that threshold, sample has low byte entropy
1239 * and can be compressible with high probability
1241 * @ENTROPY_LVL_HIGH - data are not compressible with high probability
1243 * Use of ilog2() decreases precision, we lower the LVL to 5 to compensate.
1245 #define ENTROPY_LVL_ACEPTABLE (65)
1246 #define ENTROPY_LVL_HIGH (80)
1249 * For increasead precision in shannon_entropy calculation,
1250 * let's do pow(n, M) to save more digits after comma:
1252 * - maximum int bit length is 64
1253 * - ilog2(MAX_SAMPLE_SIZE) -> 13
1254 * - 13 * 4 = 52 < 64 -> M = 4
1258 static inline u32 ilog2_w(u64 n)
1260 return ilog2(n * n * n * n);
1263 static u32 shannon_entropy(struct heuristic_ws *ws)
1265 const u32 entropy_max = 8 * ilog2_w(2);
1266 u32 entropy_sum = 0;
1267 u32 p, p_base, sz_base;
1270 sz_base = ilog2_w(ws->sample_size);
1271 for (i = 0; i < BUCKET_SIZE && ws->bucket[i].count > 0; i++) {
1272 p = ws->bucket[i].count;
1273 p_base = ilog2_w(p);
1274 entropy_sum += p * (sz_base - p_base);
1277 entropy_sum /= ws->sample_size;
1278 return entropy_sum * 100 / entropy_max;
1281 /* Compare buckets by size, ascending */
1282 static int bucket_comp_rev(const void *lv, const void *rv)
1284 const struct bucket_item *l = (const struct bucket_item *)lv;
1285 const struct bucket_item *r = (const struct bucket_item *)rv;
1287 return r->count - l->count;
1291 * Size of the core byte set - how many bytes cover 90% of the sample
1293 * There are several types of structured binary data that use nearly all byte
1294 * values. The distribution can be uniform and counts in all buckets will be
1295 * nearly the same (eg. encrypted data). Unlikely to be compressible.
1297 * Other possibility is normal (Gaussian) distribution, where the data could
1298 * be potentially compressible, but we have to take a few more steps to decide
1301 * @BYTE_CORE_SET_LOW - main part of byte values repeated frequently,
1302 * compression algo can easy fix that
1303 * @BYTE_CORE_SET_HIGH - data have uniform distribution and with high
1304 * probability is not compressible
1306 #define BYTE_CORE_SET_LOW (64)
1307 #define BYTE_CORE_SET_HIGH (200)
1309 static int byte_core_set_size(struct heuristic_ws *ws)
1312 u32 coreset_sum = 0;
1313 const u32 core_set_threshold = ws->sample_size * 90 / 100;
1314 struct bucket_item *bucket = ws->bucket;
1316 /* Sort in reverse order */
1317 sort(bucket, BUCKET_SIZE, sizeof(*bucket), &bucket_comp_rev, NULL);
1319 for (i = 0; i < BYTE_CORE_SET_LOW; i++)
1320 coreset_sum += bucket[i].count;
1322 if (coreset_sum > core_set_threshold)
1325 for (; i < BYTE_CORE_SET_HIGH && bucket[i].count > 0; i++) {
1326 coreset_sum += bucket[i].count;
1327 if (coreset_sum > core_set_threshold)
1335 * Count byte values in buckets.
1336 * This heuristic can detect textual data (configs, xml, json, html, etc).
1337 * Because in most text-like data byte set is restricted to limited number of
1338 * possible characters, and that restriction in most cases makes data easy to
1341 * @BYTE_SET_THRESHOLD - consider all data within this byte set size:
1342 * less - compressible
1343 * more - need additional analysis
1345 #define BYTE_SET_THRESHOLD (64)
1347 static u32 byte_set_size(const struct heuristic_ws *ws)
1350 u32 byte_set_size = 0;
1352 for (i = 0; i < BYTE_SET_THRESHOLD; i++) {
1353 if (ws->bucket[i].count > 0)
1358 * Continue collecting count of byte values in buckets. If the byte
1359 * set size is bigger then the threshold, it's pointless to continue,
1360 * the detection technique would fail for this type of data.
1362 for (; i < BUCKET_SIZE; i++) {
1363 if (ws->bucket[i].count > 0) {
1365 if (byte_set_size > BYTE_SET_THRESHOLD)
1366 return byte_set_size;
1370 return byte_set_size;
1373 static bool sample_repeated_patterns(struct heuristic_ws *ws)
1375 const u32 half_of_sample = ws->sample_size / 2;
1376 const u8 *data = ws->sample;
1378 return memcmp(&data[0], &data[half_of_sample], half_of_sample) == 0;
1381 static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end,
1382 struct heuristic_ws *ws)
1385 u64 index, index_end;
1386 u32 i, curr_sample_pos;
1390 * Compression handles the input data by chunks of 128KiB
1391 * (defined by BTRFS_MAX_UNCOMPRESSED)
1393 * We do the same for the heuristic and loop over the whole range.
1395 * MAX_SAMPLE_SIZE - calculated under assumption that heuristic will
1396 * process no more than BTRFS_MAX_UNCOMPRESSED at a time.
1398 if (end - start > BTRFS_MAX_UNCOMPRESSED)
1399 end = start + BTRFS_MAX_UNCOMPRESSED;
1401 index = start >> PAGE_SHIFT;
1402 index_end = end >> PAGE_SHIFT;
1404 /* Don't miss unaligned end */
1405 if (!IS_ALIGNED(end, PAGE_SIZE))
1408 curr_sample_pos = 0;
1409 while (index < index_end) {
1410 page = find_get_page(inode->i_mapping, index);
1411 in_data = kmap(page);
1412 /* Handle case where the start is not aligned to PAGE_SIZE */
1413 i = start % PAGE_SIZE;
1414 while (i < PAGE_SIZE - SAMPLING_READ_SIZE) {
1415 /* Don't sample any garbage from the last page */
1416 if (start > end - SAMPLING_READ_SIZE)
1418 memcpy(&ws->sample[curr_sample_pos], &in_data[i],
1419 SAMPLING_READ_SIZE);
1420 i += SAMPLING_INTERVAL;
1421 start += SAMPLING_INTERVAL;
1422 curr_sample_pos += SAMPLING_READ_SIZE;
1430 ws->sample_size = curr_sample_pos;
1434 * Compression heuristic.
1436 * For now is's a naive and optimistic 'return true', we'll extend the logic to
1437 * quickly (compared to direct compression) detect data characteristics
1438 * (compressible/uncompressible) to avoid wasting CPU time on uncompressible
1441 * The following types of analysis can be performed:
1442 * - detect mostly zero data
1443 * - detect data with low "byte set" size (text, etc)
1444 * - detect data with low/high "core byte" set
1446 * Return non-zero if the compression should be done, 0 otherwise.
1448 int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
1450 struct list_head *ws_list = __find_workspace(0, true);
1451 struct heuristic_ws *ws;
1456 ws = list_entry(ws_list, struct heuristic_ws, list);
1458 heuristic_collect_sample(inode, start, end, ws);
1460 if (sample_repeated_patterns(ws)) {
1465 memset(ws->bucket, 0, sizeof(*ws->bucket)*BUCKET_SIZE);
1467 for (i = 0; i < ws->sample_size; i++) {
1468 byte = ws->sample[i];
1469 ws->bucket[byte].count++;
1472 i = byte_set_size(ws);
1473 if (i < BYTE_SET_THRESHOLD) {
1478 i = byte_core_set_size(ws);
1479 if (i <= BYTE_CORE_SET_LOW) {
1484 if (i >= BYTE_CORE_SET_HIGH) {
1489 i = shannon_entropy(ws);
1490 if (i <= ENTROPY_LVL_ACEPTABLE) {
1496 * For the levels below ENTROPY_LVL_HIGH, additional analysis would be
1497 * needed to give green light to compression.
1499 * For now just assume that compression at that level is not worth the
1500 * resources because:
1502 * 1. it is possible to defrag the data later
1504 * 2. the data would turn out to be hardly compressible, eg. 150 byte
1505 * values, every bucket has counter at level ~54. The heuristic would
1506 * be confused. This can happen when data have some internal repeated
1507 * patterns like "abbacbbc...". This can be detected by analyzing
1508 * pairs of bytes, which is too costly.
1510 if (i < ENTROPY_LVL_HIGH) {
1519 __free_workspace(0, ws_list, true);
1523 unsigned int btrfs_compress_str2level(const char *str)
1525 if (strncmp(str, "zlib", 4) != 0)
1528 /* Accepted form: zlib:1 up to zlib:9 and nothing left after the number */
1529 if (str[4] == ':' && '1' <= str[5] && str[5] <= '9' && str[6] == 0)
1530 return str[5] - '0';
1532 return BTRFS_ZLIB_DEFAULT_LEVEL;