1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 2008 Oracle. All rights reserved.
4 */
5
6#include <linux/kernel.h>
7#include <linux/bio.h>
8#include <linux/file.h>
9#include <linux/fs.h>
10#include <linux/pagemap.h>
11#include <linux/pagevec.h>
12#include <linux/highmem.h>
13#include <linux/kthread.h>
14#include <linux/time.h>
15#include <linux/init.h>
16#include <linux/string.h>
17#include <linux/backing-dev.h>
18#include <linux/writeback.h>
19#include <linux/psi.h>
20#include <linux/slab.h>
21#include <linux/sched/mm.h>
22#include <linux/log2.h>
23#include <crypto/hash.h>
24#include "misc.h"
25#include "ctree.h"
26#include "fs.h"
27#include "disk-io.h"
28#include "transaction.h"
29#include "btrfs_inode.h"
30#include "bio.h"
31#include "ordered-data.h"
32#include "compression.h"
33#include "extent_io.h"
34#include "extent_map.h"
35#include "subpage.h"
36#include "zoned.h"
37#include "file-item.h"
38#include "super.h"
39
40static struct bio_set btrfs_compressed_bioset;
41
42static const char* const btrfs_compress_types[] = { "", "zlib", "lzo", "zstd" };
43
44const char* btrfs_compress_type2str(enum btrfs_compression_type type)
45{
46 switch (type) {
47 case BTRFS_COMPRESS_ZLIB:
48 case BTRFS_COMPRESS_LZO:
49 case BTRFS_COMPRESS_ZSTD:
50 case BTRFS_COMPRESS_NONE:
51 return btrfs_compress_types[type];
52 default:
53 break;
54 }
55
56 return NULL;
57}
58
59static inline struct compressed_bio *to_compressed_bio(struct btrfs_bio *bbio)
60{
61 return container_of(bbio, struct compressed_bio, bbio);
62}
63
64static struct compressed_bio *alloc_compressed_bio(struct btrfs_inode *inode,
65 u64 start, blk_opf_t op,
66 btrfs_bio_end_io_t end_io)
67{
68 struct btrfs_bio *bbio;
69
70 bbio = btrfs_bio(bio: bio_alloc_bioset(NULL, BTRFS_MAX_COMPRESSED_PAGES, opf: op,
71 GFP_NOFS, bs: &btrfs_compressed_bioset));
72 btrfs_bio_init(bbio, fs_info: inode->root->fs_info, end_io, NULL);
73 bbio->inode = inode;
74 bbio->file_offset = start;
75 return to_compressed_bio(bbio);
76}
77
78bool btrfs_compress_is_valid_type(const char *str, size_t len)
79{
80 int i;
81
82 for (i = 1; i < ARRAY_SIZE(btrfs_compress_types); i++) {
83 size_t comp_len = strlen(btrfs_compress_types[i]);
84
85 if (len < comp_len)
86 continue;
87
88 if (!strncmp(btrfs_compress_types[i], str, comp_len))
89 return true;
90 }
91 return false;
92}
93
94static int compression_compress_pages(int type, struct list_head *ws,
95 struct address_space *mapping, u64 start, struct page **pages,
96 unsigned long *out_pages, unsigned long *total_in,
97 unsigned long *total_out)
98{
99 switch (type) {
100 case BTRFS_COMPRESS_ZLIB:
101 return zlib_compress_pages(ws, mapping, start, pages,
102 out_pages, total_in, total_out);
103 case BTRFS_COMPRESS_LZO:
104 return lzo_compress_pages(ws, mapping, start, pages,
105 out_pages, total_in, total_out);
106 case BTRFS_COMPRESS_ZSTD:
107 return zstd_compress_pages(ws, mapping, start, pages,
108 out_pages, total_in, total_out);
109 case BTRFS_COMPRESS_NONE:
110 default:
111 /*
112 * This can happen when compression races with remount setting
113 * it to 'no compress', while caller doesn't call
114 * inode_need_compress() to check if we really need to
115 * compress.
116 *
117 * Not a big deal, just need to inform caller that we
118 * haven't allocated any pages yet.
119 */
120 *out_pages = 0;
121 return -E2BIG;
122 }
123}
124
125static int compression_decompress_bio(struct list_head *ws,
126 struct compressed_bio *cb)
127{
128 switch (cb->compress_type) {
129 case BTRFS_COMPRESS_ZLIB: return zlib_decompress_bio(ws, cb);
130 case BTRFS_COMPRESS_LZO: return lzo_decompress_bio(ws, cb);
131 case BTRFS_COMPRESS_ZSTD: return zstd_decompress_bio(ws, cb);
132 case BTRFS_COMPRESS_NONE:
133 default:
134 /*
135 * This can't happen, the type is validated several times
136 * before we get here.
137 */
138 BUG();
139 }
140}
141
142static int compression_decompress(int type, struct list_head *ws,
143 const u8 *data_in, struct page *dest_page,
144 unsigned long start_byte, size_t srclen, size_t destlen)
145{
146 switch (type) {
147 case BTRFS_COMPRESS_ZLIB: return zlib_decompress(ws, data_in, dest_page,
148 start_byte, srclen, destlen);
149 case BTRFS_COMPRESS_LZO: return lzo_decompress(ws, data_in, dest_page,
150 start_byte, srclen, destlen);
151 case BTRFS_COMPRESS_ZSTD: return zstd_decompress(ws, data_in, dest_page,
152 start_byte, srclen, destlen);
153 case BTRFS_COMPRESS_NONE:
154 default:
155 /*
156 * This can't happen, the type is validated several times
157 * before we get here.
158 */
159 BUG();
160 }
161}
162
163static void btrfs_free_compressed_pages(struct compressed_bio *cb)
164{
165 for (unsigned int i = 0; i < cb->nr_pages; i++)
166 put_page(page: cb->compressed_pages[i]);
167 kfree(objp: cb->compressed_pages);
168}
169
170static int btrfs_decompress_bio(struct compressed_bio *cb);
171
172static void end_compressed_bio_read(struct btrfs_bio *bbio)
173{
174 struct compressed_bio *cb = to_compressed_bio(bbio);
175 blk_status_t status = bbio->bio.bi_status;
176
177 if (!status)
178 status = errno_to_blk_status(errno: btrfs_decompress_bio(cb));
179
180 btrfs_free_compressed_pages(cb);
181 btrfs_bio_end_io(bbio: cb->orig_bbio, status);
182 bio_put(&bbio->bio);
183}
184
185/*
186 * Clear the writeback bits on all of the file
187 * pages for a compressed write
188 */
189static noinline void end_compressed_writeback(const struct compressed_bio *cb)
190{
191 struct inode *inode = &cb->bbio.inode->vfs_inode;
192 struct btrfs_fs_info *fs_info = btrfs_sb(sb: inode->i_sb);
193 unsigned long index = cb->start >> PAGE_SHIFT;
194 unsigned long end_index = (cb->start + cb->len - 1) >> PAGE_SHIFT;
195 struct folio_batch fbatch;
196 const int error = blk_status_to_errno(status: cb->bbio.bio.bi_status);
197 int i;
198 int ret;
199
200 if (error)
201 mapping_set_error(mapping: inode->i_mapping, error);
202
203 folio_batch_init(fbatch: &fbatch);
204 while (index <= end_index) {
205 ret = filemap_get_folios(mapping: inode->i_mapping, start: &index, end: end_index,
206 fbatch: &fbatch);
207
208 if (ret == 0)
209 return;
210
211 for (i = 0; i < ret; i++) {
212 struct folio *folio = fbatch.folios[i];
213
214 btrfs_page_clamp_clear_writeback(fs_info, page: &folio->page,
215 start: cb->start, len: cb->len);
216 }
217 folio_batch_release(fbatch: &fbatch);
218 }
219 /* the inode may be gone now */
220}
221
222static void btrfs_finish_compressed_write_work(struct work_struct *work)
223{
224 struct compressed_bio *cb =
225 container_of(work, struct compressed_bio, write_end_work);
226
227 btrfs_finish_ordered_extent(ordered: cb->bbio.ordered, NULL, file_offset: cb->start, len: cb->len,
228 uptodate: cb->bbio.bio.bi_status == BLK_STS_OK);
229
230 if (cb->writeback)
231 end_compressed_writeback(cb);
232 /* Note, our inode could be gone now */
233
234 btrfs_free_compressed_pages(cb);
235 bio_put(&cb->bbio.bio);
236}
237
238/*
239 * Do the cleanup once all the compressed pages hit the disk. This will clear
240 * writeback on the file pages and free the compressed pages.
241 *
242 * This also calls the writeback end hooks for the file pages so that metadata
243 * and checksums can be updated in the file.
244 */
245static void end_compressed_bio_write(struct btrfs_bio *bbio)
246{
247 struct compressed_bio *cb = to_compressed_bio(bbio);
248 struct btrfs_fs_info *fs_info = bbio->inode->root->fs_info;
249
250 queue_work(wq: fs_info->compressed_write_workers, work: &cb->write_end_work);
251}
252
253static void btrfs_add_compressed_bio_pages(struct compressed_bio *cb)
254{
255 struct bio *bio = &cb->bbio.bio;
256 u32 offset = 0;
257
258 while (offset < cb->compressed_len) {
259 u32 len = min_t(u32, cb->compressed_len - offset, PAGE_SIZE);
260
261 /* Maximum compressed extent is smaller than bio size limit. */
262 __bio_add_page(bio, page: cb->compressed_pages[offset >> PAGE_SHIFT],
263 len, off: 0);
264 offset += len;
265 }
266}
267
268/*
269 * worker function to build and submit bios for previously compressed pages.
270 * The corresponding pages in the inode should be marked for writeback
271 * and the compressed pages should have a reference on them for dropping
272 * when the IO is complete.
273 *
274 * This also checksums the file bytes and gets things ready for
275 * the end io hooks.
276 */
277void btrfs_submit_compressed_write(struct btrfs_ordered_extent *ordered,
278 struct page **compressed_pages,
279 unsigned int nr_pages,
280 blk_opf_t write_flags,
281 bool writeback)
282{
283 struct btrfs_inode *inode = BTRFS_I(inode: ordered->inode);
284 struct btrfs_fs_info *fs_info = inode->root->fs_info;
285 struct compressed_bio *cb;
286
287 ASSERT(IS_ALIGNED(ordered->file_offset, fs_info->sectorsize));
288 ASSERT(IS_ALIGNED(ordered->num_bytes, fs_info->sectorsize));
289
290 cb = alloc_compressed_bio(inode, start: ordered->file_offset,
291 op: REQ_OP_WRITE | write_flags,
292 end_io: end_compressed_bio_write);
293 cb->start = ordered->file_offset;
294 cb->len = ordered->num_bytes;
295 cb->compressed_pages = compressed_pages;
296 cb->compressed_len = ordered->disk_num_bytes;
297 cb->writeback = writeback;
298 INIT_WORK(&cb->write_end_work, btrfs_finish_compressed_write_work);
299 cb->nr_pages = nr_pages;
300 cb->bbio.bio.bi_iter.bi_sector = ordered->disk_bytenr >> SECTOR_SHIFT;
301 cb->bbio.ordered = ordered;
302 btrfs_add_compressed_bio_pages(cb);
303
304 btrfs_submit_bio(bbio: &cb->bbio, mirror_num: 0);
305}
306
307/*
308 * Add extra pages in the same compressed file extent so that we don't need to
309 * re-read the same extent again and again.
310 *
311 * NOTE: this won't work well for subpage, as for subpage read, we lock the
312 * full page then submit bio for each compressed/regular extents.
313 *
314 * This means, if we have several sectors in the same page points to the same
315 * on-disk compressed data, we will re-read the same extent many times and
316 * this function can only help for the next page.
317 */
318static noinline int add_ra_bio_pages(struct inode *inode,
319 u64 compressed_end,
320 struct compressed_bio *cb,
321 int *memstall, unsigned long *pflags)
322{
323 struct btrfs_fs_info *fs_info = btrfs_sb(sb: inode->i_sb);
324 unsigned long end_index;
325 struct bio *orig_bio = &cb->orig_bbio->bio;
326 u64 cur = cb->orig_bbio->file_offset + orig_bio->bi_iter.bi_size;
327 u64 isize = i_size_read(inode);
328 int ret;
329 struct page *page;
330 struct extent_map *em;
331 struct address_space *mapping = inode->i_mapping;
332 struct extent_map_tree *em_tree;
333 struct extent_io_tree *tree;
334 int sectors_missed = 0;
335
336 em_tree = &BTRFS_I(inode)->extent_tree;
337 tree = &BTRFS_I(inode)->io_tree;
338
339 if (isize == 0)
340 return 0;
341
342 /*
343 * For current subpage support, we only support 64K page size,
344 * which means maximum compressed extent size (128K) is just 2x page
345 * size.
346 * This makes readahead less effective, so here disable readahead for
347 * subpage for now, until full compressed write is supported.
348 */
349 if (btrfs_sb(sb: inode->i_sb)->sectorsize < PAGE_SIZE)
350 return 0;
351
352 end_index = (i_size_read(inode) - 1) >> PAGE_SHIFT;
353
354 while (cur < compressed_end) {
355 u64 page_end;
356 u64 pg_index = cur >> PAGE_SHIFT;
357 u32 add_size;
358
359 if (pg_index > end_index)
360 break;
361
362 page = xa_load(&mapping->i_pages, index: pg_index);
363 if (page && !xa_is_value(entry: page)) {
364 sectors_missed += (PAGE_SIZE - offset_in_page(cur)) >>
365 fs_info->sectorsize_bits;
366
367 /* Beyond threshold, no need to continue */
368 if (sectors_missed > 4)
369 break;
370
371 /*
372 * Jump to next page start as we already have page for
373 * current offset.
374 */
375 cur = (pg_index << PAGE_SHIFT) + PAGE_SIZE;
376 continue;
377 }
378
379 page = __page_cache_alloc(gfp: mapping_gfp_constraint(mapping,
380 gfp_mask: ~__GFP_FS));
381 if (!page)
382 break;
383
384 if (add_to_page_cache_lru(page, mapping, index: pg_index, GFP_NOFS)) {
385 put_page(page);
386 /* There is already a page, skip to page end */
387 cur = (pg_index << PAGE_SHIFT) + PAGE_SIZE;
388 continue;
389 }
390
391 if (!*memstall && PageWorkingset(page)) {
392 psi_memstall_enter(flags: pflags);
393 *memstall = 1;
394 }
395
396 ret = set_page_extent_mapped(page);
397 if (ret < 0) {
398 unlock_page(page);
399 put_page(page);
400 break;
401 }
402
403 page_end = (pg_index << PAGE_SHIFT) + PAGE_SIZE - 1;
404 lock_extent(tree, start: cur, end: page_end, NULL);
405 read_lock(&em_tree->lock);
406 em = lookup_extent_mapping(tree: em_tree, start: cur, len: page_end + 1 - cur);
407 read_unlock(&em_tree->lock);
408
409 /*
410 * At this point, we have a locked page in the page cache for
411 * these bytes in the file. But, we have to make sure they map
412 * to this compressed extent on disk.
413 */
414 if (!em || cur < em->start ||
415 (cur + fs_info->sectorsize > extent_map_end(em)) ||
416 (em->block_start >> SECTOR_SHIFT) != orig_bio->bi_iter.bi_sector) {
417 free_extent_map(em);
418 unlock_extent(tree, start: cur, end: page_end, NULL);
419 unlock_page(page);
420 put_page(page);
421 break;
422 }
423 free_extent_map(em);
424
425 if (page->index == end_index) {
426 size_t zero_offset = offset_in_page(isize);
427
428 if (zero_offset) {
429 int zeros;
430 zeros = PAGE_SIZE - zero_offset;
431 memzero_page(page, offset: zero_offset, len: zeros);
432 }
433 }
434
435 add_size = min(em->start + em->len, page_end + 1) - cur;
436 ret = bio_add_page(bio: orig_bio, page, len: add_size, offset_in_page(cur));
437 if (ret != add_size) {
438 unlock_extent(tree, start: cur, end: page_end, NULL);
439 unlock_page(page);
440 put_page(page);
441 break;
442 }
443 /*
444 * If it's subpage, we also need to increase its
445 * subpage::readers number, as at endio we will decrease
446 * subpage::readers and to unlock the page.
447 */
448 if (fs_info->sectorsize < PAGE_SIZE)
449 btrfs_subpage_start_reader(fs_info, page, start: cur, len: add_size);
450 put_page(page);
451 cur += add_size;
452 }
453 return 0;
454}
455
456/*
457 * for a compressed read, the bio we get passed has all the inode pages
458 * in it. We don't actually do IO on those pages but allocate new ones
459 * to hold the compressed pages on disk.
460 *
461 * bio->bi_iter.bi_sector points to the compressed extent on disk
462 * bio->bi_io_vec points to all of the inode pages
463 *
464 * After the compressed pages are read, we copy the bytes into the
465 * bio we were passed and then call the bio end_io calls
466 */
467void btrfs_submit_compressed_read(struct btrfs_bio *bbio)
468{
469 struct btrfs_inode *inode = bbio->inode;
470 struct btrfs_fs_info *fs_info = inode->root->fs_info;
471 struct extent_map_tree *em_tree = &inode->extent_tree;
472 struct compressed_bio *cb;
473 unsigned int compressed_len;
474 u64 file_offset = bbio->file_offset;
475 u64 em_len;
476 u64 em_start;
477 struct extent_map *em;
478 unsigned long pflags;
479 int memstall = 0;
480 blk_status_t ret;
481 int ret2;
482
483 /* we need the actual starting offset of this extent in the file */
484 read_lock(&em_tree->lock);
485 em = lookup_extent_mapping(tree: em_tree, start: file_offset, len: fs_info->sectorsize);
486 read_unlock(&em_tree->lock);
487 if (!em) {
488 ret = BLK_STS_IOERR;
489 goto out;
490 }
491
492 ASSERT(em->compress_type != BTRFS_COMPRESS_NONE);
493 compressed_len = em->block_len;
494
495 cb = alloc_compressed_bio(inode, start: file_offset, op: REQ_OP_READ,
496 end_io: end_compressed_bio_read);
497
498 cb->start = em->orig_start;
499 em_len = em->len;
500 em_start = em->start;
501
502 cb->len = bbio->bio.bi_iter.bi_size;
503 cb->compressed_len = compressed_len;
504 cb->compress_type = em->compress_type;
505 cb->orig_bbio = bbio;
506
507 free_extent_map(em);
508
509 cb->nr_pages = DIV_ROUND_UP(compressed_len, PAGE_SIZE);
510 cb->compressed_pages = kcalloc(n: cb->nr_pages, size: sizeof(struct page *), GFP_NOFS);
511 if (!cb->compressed_pages) {
512 ret = BLK_STS_RESOURCE;
513 goto out_free_bio;
514 }
515
516 ret2 = btrfs_alloc_page_array(nr_pages: cb->nr_pages, page_array: cb->compressed_pages);
517 if (ret2) {
518 ret = BLK_STS_RESOURCE;
519 goto out_free_compressed_pages;
520 }
521
522 add_ra_bio_pages(inode: &inode->vfs_inode, compressed_end: em_start + em_len, cb, memstall: &memstall,
523 pflags: &pflags);
524
525 /* include any pages we added in add_ra-bio_pages */
526 cb->len = bbio->bio.bi_iter.bi_size;
527 cb->bbio.bio.bi_iter.bi_sector = bbio->bio.bi_iter.bi_sector;
528 btrfs_add_compressed_bio_pages(cb);
529
530 if (memstall)
531 psi_memstall_leave(flags: &pflags);
532
533 btrfs_submit_bio(bbio: &cb->bbio, mirror_num: 0);
534 return;
535
536out_free_compressed_pages:
537 kfree(objp: cb->compressed_pages);
538out_free_bio:
539 bio_put(&cb->bbio.bio);
540out:
541 btrfs_bio_end_io(bbio, status: ret);
542}
543
544/*
545 * Heuristic uses systematic sampling to collect data from the input data
546 * range, the logic can be tuned by the following constants:
547 *
548 * @SAMPLING_READ_SIZE - how many bytes will be copied from for each sample
549 * @SAMPLING_INTERVAL - range from which the sampled data can be collected
550 */
551#define SAMPLING_READ_SIZE (16)
552#define SAMPLING_INTERVAL (256)
553
554/*
555 * For statistical analysis of the input data we consider bytes that form a
556 * Galois Field of 256 objects. Each object has an attribute count, ie. how
557 * many times the object appeared in the sample.
558 */
559#define BUCKET_SIZE (256)
560
561/*
562 * The size of the sample is based on a statistical sampling rule of thumb.
563 * The common way is to perform sampling tests as long as the number of
564 * elements in each cell is at least 5.
565 *
566 * Instead of 5, we choose 32 to obtain more accurate results.
567 * If the data contain the maximum number of symbols, which is 256, we obtain a
568 * sample size bound by 8192.
569 *
570 * For a sample of at most 8KB of data per data range: 16 consecutive bytes
571 * from up to 512 locations.
572 */
573#define MAX_SAMPLE_SIZE (BTRFS_MAX_UNCOMPRESSED * \
574 SAMPLING_READ_SIZE / SAMPLING_INTERVAL)
575
576struct bucket_item {
577 u32 count;
578};
579
580struct heuristic_ws {
581 /* Partial copy of input data */
582 u8 *sample;
583 u32 sample_size;
584 /* Buckets store counters for each byte value */
585 struct bucket_item *bucket;
586 /* Sorting buffer */
587 struct bucket_item *bucket_b;
588 struct list_head list;
589};
590
591static struct workspace_manager heuristic_wsm;
592
593static void free_heuristic_ws(struct list_head *ws)
594{
595 struct heuristic_ws *workspace;
596
597 workspace = list_entry(ws, struct heuristic_ws, list);
598
599 kvfree(addr: workspace->sample);
600 kfree(objp: workspace->bucket);
601 kfree(objp: workspace->bucket_b);
602 kfree(objp: workspace);
603}
604
605static struct list_head *alloc_heuristic_ws(unsigned int level)
606{
607 struct heuristic_ws *ws;
608
609 ws = kzalloc(size: sizeof(*ws), GFP_KERNEL);
610 if (!ws)
611 return ERR_PTR(error: -ENOMEM);
612
613 ws->sample = kvmalloc(MAX_SAMPLE_SIZE, GFP_KERNEL);
614 if (!ws->sample)
615 goto fail;
616
617 ws->bucket = kcalloc(BUCKET_SIZE, size: sizeof(*ws->bucket), GFP_KERNEL);
618 if (!ws->bucket)
619 goto fail;
620
621 ws->bucket_b = kcalloc(BUCKET_SIZE, size: sizeof(*ws->bucket_b), GFP_KERNEL);
622 if (!ws->bucket_b)
623 goto fail;
624
625 INIT_LIST_HEAD(list: &ws->list);
626 return &ws->list;
627fail:
628 free_heuristic_ws(ws: &ws->list);
629 return ERR_PTR(error: -ENOMEM);
630}
631
632const struct btrfs_compress_op btrfs_heuristic_compress = {
633 .workspace_manager = &heuristic_wsm,
634};
635
636static const struct btrfs_compress_op * const btrfs_compress_op[] = {
637 /* The heuristic is represented as compression type 0 */
638 &btrfs_heuristic_compress,
639 &btrfs_zlib_compress,
640 &btrfs_lzo_compress,
641 &btrfs_zstd_compress,
642};
643
644static struct list_head *alloc_workspace(int type, unsigned int level)
645{
646 switch (type) {
647 case BTRFS_COMPRESS_NONE: return alloc_heuristic_ws(level);
648 case BTRFS_COMPRESS_ZLIB: return zlib_alloc_workspace(level);
649 case BTRFS_COMPRESS_LZO: return lzo_alloc_workspace(level);
650 case BTRFS_COMPRESS_ZSTD: return zstd_alloc_workspace(level);
651 default:
652 /*
653 * This can't happen, the type is validated several times
654 * before we get here.
655 */
656 BUG();
657 }
658}
659
660static void free_workspace(int type, struct list_head *ws)
661{
662 switch (type) {
663 case BTRFS_COMPRESS_NONE: return free_heuristic_ws(ws);
664 case BTRFS_COMPRESS_ZLIB: return zlib_free_workspace(ws);
665 case BTRFS_COMPRESS_LZO: return lzo_free_workspace(ws);
666 case BTRFS_COMPRESS_ZSTD: return zstd_free_workspace(ws);
667 default:
668 /*
669 * This can't happen, the type is validated several times
670 * before we get here.
671 */
672 BUG();
673 }
674}
675
676static void btrfs_init_workspace_manager(int type)
677{
678 struct workspace_manager *wsm;
679 struct list_head *workspace;
680
681 wsm = btrfs_compress_op[type]->workspace_manager;
682 INIT_LIST_HEAD(list: &wsm->idle_ws);
683 spin_lock_init(&wsm->ws_lock);
684 atomic_set(v: &wsm->total_ws, i: 0);
685 init_waitqueue_head(&wsm->ws_wait);
686
687 /*
688 * Preallocate one workspace for each compression type so we can
689 * guarantee forward progress in the worst case
690 */
691 workspace = alloc_workspace(type, level: 0);
692 if (IS_ERR(ptr: workspace)) {
693 pr_warn(
694 "BTRFS: cannot preallocate compression workspace, will try later\n");
695 } else {
696 atomic_set(v: &wsm->total_ws, i: 1);
697 wsm->free_ws = 1;
698 list_add(new: workspace, head: &wsm->idle_ws);
699 }
700}
701
702static void btrfs_cleanup_workspace_manager(int type)
703{
704 struct workspace_manager *wsman;
705 struct list_head *ws;
706
707 wsman = btrfs_compress_op[type]->workspace_manager;
708 while (!list_empty(head: &wsman->idle_ws)) {
709 ws = wsman->idle_ws.next;
710 list_del(entry: ws);
711 free_workspace(type, ws);
712 atomic_dec(v: &wsman->total_ws);
713 }
714}
715
716/*
717 * This finds an available workspace or allocates a new one.
718 * If it's not possible to allocate a new one, waits until there's one.
719 * Preallocation makes a forward progress guarantees and we do not return
720 * errors.
721 */
722struct list_head *btrfs_get_workspace(int type, unsigned int level)
723{
724 struct workspace_manager *wsm;
725 struct list_head *workspace;
726 int cpus = num_online_cpus();
727 unsigned nofs_flag;
728 struct list_head *idle_ws;
729 spinlock_t *ws_lock;
730 atomic_t *total_ws;
731 wait_queue_head_t *ws_wait;
732 int *free_ws;
733
734 wsm = btrfs_compress_op[type]->workspace_manager;
735 idle_ws = &wsm->idle_ws;
736 ws_lock = &wsm->ws_lock;
737 total_ws = &wsm->total_ws;
738 ws_wait = &wsm->ws_wait;
739 free_ws = &wsm->free_ws;
740
741again:
742 spin_lock(lock: ws_lock);
743 if (!list_empty(head: idle_ws)) {
744 workspace = idle_ws->next;
745 list_del(entry: workspace);
746 (*free_ws)--;
747 spin_unlock(lock: ws_lock);
748 return workspace;
749
750 }
751 if (atomic_read(v: total_ws) > cpus) {
752 DEFINE_WAIT(wait);
753
754 spin_unlock(lock: ws_lock);
755 prepare_to_wait(wq_head: ws_wait, wq_entry: &wait, TASK_UNINTERRUPTIBLE);
756 if (atomic_read(v: total_ws) > cpus && !*free_ws)
757 schedule();
758 finish_wait(wq_head: ws_wait, wq_entry: &wait);
759 goto again;
760 }
761 atomic_inc(v: total_ws);
762 spin_unlock(lock: ws_lock);
763
764 /*
765 * Allocation helpers call vmalloc that can't use GFP_NOFS, so we have
766 * to turn it off here because we might get called from the restricted
767 * context of btrfs_compress_bio/btrfs_compress_pages
768 */
769 nofs_flag = memalloc_nofs_save();
770 workspace = alloc_workspace(type, level);
771 memalloc_nofs_restore(flags: nofs_flag);
772
773 if (IS_ERR(ptr: workspace)) {
774 atomic_dec(v: total_ws);
775 wake_up(ws_wait);
776
777 /*
778 * Do not return the error but go back to waiting. There's a
779 * workspace preallocated for each type and the compression
780 * time is bounded so we get to a workspace eventually. This
781 * makes our caller's life easier.
782 *
783 * To prevent silent and low-probability deadlocks (when the
784 * initial preallocation fails), check if there are any
785 * workspaces at all.
786 */
787 if (atomic_read(v: total_ws) == 0) {
788 static DEFINE_RATELIMIT_STATE(_rs,
789 /* once per minute */ 60 * HZ,
790 /* no burst */ 1);
791
792 if (__ratelimit(&_rs)) {
793 pr_warn("BTRFS: no compression workspaces, low memory, retrying\n");
794 }
795 }
796 goto again;
797 }
798 return workspace;
799}
800
801static struct list_head *get_workspace(int type, int level)
802{
803 switch (type) {
804 case BTRFS_COMPRESS_NONE: return btrfs_get_workspace(type, level);
805 case BTRFS_COMPRESS_ZLIB: return zlib_get_workspace(level);
806 case BTRFS_COMPRESS_LZO: return btrfs_get_workspace(type, level);
807 case BTRFS_COMPRESS_ZSTD: return zstd_get_workspace(level);
808 default:
809 /*
810 * This can't happen, the type is validated several times
811 * before we get here.
812 */
813 BUG();
814 }
815}
816
817/*
818 * put a workspace struct back on the list or free it if we have enough
819 * idle ones sitting around
820 */
821void btrfs_put_workspace(int type, struct list_head *ws)
822{
823 struct workspace_manager *wsm;
824 struct list_head *idle_ws;
825 spinlock_t *ws_lock;
826 atomic_t *total_ws;
827 wait_queue_head_t *ws_wait;
828 int *free_ws;
829
830 wsm = btrfs_compress_op[type]->workspace_manager;
831 idle_ws = &wsm->idle_ws;
832 ws_lock = &wsm->ws_lock;
833 total_ws = &wsm->total_ws;
834 ws_wait = &wsm->ws_wait;
835 free_ws = &wsm->free_ws;
836
837 spin_lock(lock: ws_lock);
838 if (*free_ws <= num_online_cpus()) {
839 list_add(new: ws, head: idle_ws);
840 (*free_ws)++;
841 spin_unlock(lock: ws_lock);
842 goto wake;
843 }
844 spin_unlock(lock: ws_lock);
845
846 free_workspace(type, ws);
847 atomic_dec(v: total_ws);
848wake:
849 cond_wake_up(wq: ws_wait);
850}
851
852static void put_workspace(int type, struct list_head *ws)
853{
854 switch (type) {
855 case BTRFS_COMPRESS_NONE: return btrfs_put_workspace(type, ws);
856 case BTRFS_COMPRESS_ZLIB: return btrfs_put_workspace(type, ws);
857 case BTRFS_COMPRESS_LZO: return btrfs_put_workspace(type, ws);
858 case BTRFS_COMPRESS_ZSTD: return zstd_put_workspace(ws);
859 default:
860 /*
861 * This can't happen, the type is validated several times
862 * before we get here.
863 */
864 BUG();
865 }
866}
867
868/*
869 * Adjust @level according to the limits of the compression algorithm or
870 * fallback to default
871 */
872static unsigned int btrfs_compress_set_level(int type, unsigned level)
873{
874 const struct btrfs_compress_op *ops = btrfs_compress_op[type];
875
876 if (level == 0)
877 level = ops->default_level;
878 else
879 level = min(level, ops->max_level);
880
881 return level;
882}
883
884/*
885 * Given an address space and start and length, compress the bytes into @pages
886 * that are allocated on demand.
887 *
888 * @type_level is encoded algorithm and level, where level 0 means whatever
889 * default the algorithm chooses and is opaque here;
890 * - compression algo are 0-3
891 * - the level are bits 4-7
892 *
893 * @out_pages is an in/out parameter, holds maximum number of pages to allocate
894 * and returns number of actually allocated pages
895 *
896 * @total_in is used to return the number of bytes actually read. It
897 * may be smaller than the input length if we had to exit early because we
898 * ran out of room in the pages array or because we cross the
899 * max_out threshold.
900 *
901 * @total_out is an in/out parameter, must be set to the input length and will
902 * be also used to return the total number of compressed bytes
903 */
904int btrfs_compress_pages(unsigned int type_level, struct address_space *mapping,
905 u64 start, struct page **pages,
906 unsigned long *out_pages,
907 unsigned long *total_in,
908 unsigned long *total_out)
909{
910 int type = btrfs_compress_type(type_level);
911 int level = btrfs_compress_level(type_level);
912 struct list_head *workspace;
913 int ret;
914
915 level = btrfs_compress_set_level(type, level);
916 workspace = get_workspace(type, level);
917 ret = compression_compress_pages(type, ws: workspace, mapping, start, pages,
918 out_pages, total_in, total_out);
919 put_workspace(type, ws: workspace);
920 return ret;
921}
922
923static int btrfs_decompress_bio(struct compressed_bio *cb)
924{
925 struct list_head *workspace;
926 int ret;
927 int type = cb->compress_type;
928
929 workspace = get_workspace(type, level: 0);
930 ret = compression_decompress_bio(ws: workspace, cb);
931 put_workspace(type, ws: workspace);
932
933 if (!ret)
934 zero_fill_bio(bio: &cb->orig_bbio->bio);
935 return ret;
936}
937
938/*
939 * a less complex decompression routine. Our compressed data fits in a
940 * single page, and we want to read a single page out of it.
941 * start_byte tells us the offset into the compressed data we're interested in
942 */
943int btrfs_decompress(int type, const u8 *data_in, struct page *dest_page,
944 unsigned long start_byte, size_t srclen, size_t destlen)
945{
946 struct list_head *workspace;
947 int ret;
948
949 workspace = get_workspace(type, level: 0);
950 ret = compression_decompress(type, ws: workspace, data_in, dest_page,
951 start_byte, srclen, destlen);
952 put_workspace(type, ws: workspace);
953
954 return ret;
955}
956
957int __init btrfs_init_compress(void)
958{
959 if (bioset_init(&btrfs_compressed_bioset, BIO_POOL_SIZE,
960 offsetof(struct compressed_bio, bbio.bio),
961 flags: BIOSET_NEED_BVECS))
962 return -ENOMEM;
963 btrfs_init_workspace_manager(type: BTRFS_COMPRESS_NONE);
964 btrfs_init_workspace_manager(type: BTRFS_COMPRESS_ZLIB);
965 btrfs_init_workspace_manager(type: BTRFS_COMPRESS_LZO);
966 zstd_init_workspace_manager();
967 return 0;
968}
969
970void __cold btrfs_exit_compress(void)
971{
972 btrfs_cleanup_workspace_manager(type: BTRFS_COMPRESS_NONE);
973 btrfs_cleanup_workspace_manager(type: BTRFS_COMPRESS_ZLIB);
974 btrfs_cleanup_workspace_manager(type: BTRFS_COMPRESS_LZO);
975 zstd_cleanup_workspace_manager();
976 bioset_exit(&btrfs_compressed_bioset);
977}
978
979/*
980 * Copy decompressed data from working buffer to pages.
981 *
982 * @buf: The decompressed data buffer
983 * @buf_len: The decompressed data length
984 * @decompressed: Number of bytes that are already decompressed inside the
985 * compressed extent
986 * @cb: The compressed extent descriptor
987 * @orig_bio: The original bio that the caller wants to read for
988 *
989 * An easier to understand graph is like below:
990 *
991 * |<- orig_bio ->| |<- orig_bio->|
992 * |<------- full decompressed extent ----->|
993 * |<----------- @cb range ---->|
994 * | |<-- @buf_len -->|
995 * |<--- @decompressed --->|
996 *
997 * Note that, @cb can be a subpage of the full decompressed extent, but
998 * @cb->start always has the same as the orig_file_offset value of the full
999 * decompressed extent.
1000 *
1001 * When reading compressed extent, we have to read the full compressed extent,
1002 * while @orig_bio may only want part of the range.
1003 * Thus this function will ensure only data covered by @orig_bio will be copied
1004 * to.
1005 *
1006 * Return 0 if we have copied all needed contents for @orig_bio.
1007 * Return >0 if we need continue decompress.
1008 */
1009int btrfs_decompress_buf2page(const char *buf, u32 buf_len,
1010 struct compressed_bio *cb, u32 decompressed)
1011{
1012 struct bio *orig_bio = &cb->orig_bbio->bio;
1013 /* Offset inside the full decompressed extent */
1014 u32 cur_offset;
1015
1016 cur_offset = decompressed;
1017 /* The main loop to do the copy */
1018 while (cur_offset < decompressed + buf_len) {
1019 struct bio_vec bvec;
1020 size_t copy_len;
1021 u32 copy_start;
1022 /* Offset inside the full decompressed extent */
1023 u32 bvec_offset;
1024
1025 bvec = bio_iter_iovec(orig_bio, orig_bio->bi_iter);
1026 /*
1027 * cb->start may underflow, but subtracting that value can still
1028 * give us correct offset inside the full decompressed extent.
1029 */
1030 bvec_offset = page_offset(page: bvec.bv_page) + bvec.bv_offset - cb->start;
1031
1032 /* Haven't reached the bvec range, exit */
1033 if (decompressed + buf_len <= bvec_offset)
1034 return 1;
1035
1036 copy_start = max(cur_offset, bvec_offset);
1037 copy_len = min(bvec_offset + bvec.bv_len,
1038 decompressed + buf_len) - copy_start;
1039 ASSERT(copy_len);
1040
1041 /*
1042 * Extra range check to ensure we didn't go beyond
1043 * @buf + @buf_len.
1044 */
1045 ASSERT(copy_start - decompressed < buf_len);
1046 memcpy_to_page(page: bvec.bv_page, offset: bvec.bv_offset,
1047 from: buf + copy_start - decompressed, len: copy_len);
1048 cur_offset += copy_len;
1049
1050 bio_advance(bio: orig_bio, nbytes: copy_len);
1051 /* Finished the bio */
1052 if (!orig_bio->bi_iter.bi_size)
1053 return 0;
1054 }
1055 return 1;
1056}
1057
1058/*
1059 * Shannon Entropy calculation
1060 *
1061 * Pure byte distribution analysis fails to determine compressibility of data.
1062 * Try calculating entropy to estimate the average minimum number of bits
1063 * needed to encode the sampled data.
1064 *
1065 * For convenience, return the percentage of needed bits, instead of amount of
1066 * bits directly.
1067 *
1068 * @ENTROPY_LVL_ACEPTABLE - below that threshold, sample has low byte entropy
1069 * and can be compressible with high probability
1070 *
1071 * @ENTROPY_LVL_HIGH - data are not compressible with high probability
1072 *
1073 * Use of ilog2() decreases precision, we lower the LVL to 5 to compensate.
1074 */
1075#define ENTROPY_LVL_ACEPTABLE (65)
1076#define ENTROPY_LVL_HIGH (80)
1077
1078/*
1079 * For increasead precision in shannon_entropy calculation,
1080 * let's do pow(n, M) to save more digits after comma:
1081 *
1082 * - maximum int bit length is 64
1083 * - ilog2(MAX_SAMPLE_SIZE) -> 13
1084 * - 13 * 4 = 52 < 64 -> M = 4
1085 *
1086 * So use pow(n, 4).
1087 */
1088static inline u32 ilog2_w(u64 n)
1089{
1090 return ilog2(n * n * n * n);
1091}
1092
1093static u32 shannon_entropy(struct heuristic_ws *ws)
1094{
1095 const u32 entropy_max = 8 * ilog2_w(n: 2);
1096 u32 entropy_sum = 0;
1097 u32 p, p_base, sz_base;
1098 u32 i;
1099
1100 sz_base = ilog2_w(n: ws->sample_size);
1101 for (i = 0; i < BUCKET_SIZE && ws->bucket[i].count > 0; i++) {
1102 p = ws->bucket[i].count;
1103 p_base = ilog2_w(n: p);
1104 entropy_sum += p * (sz_base - p_base);
1105 }
1106
1107 entropy_sum /= ws->sample_size;
1108 return entropy_sum * 100 / entropy_max;
1109}
1110
1111#define RADIX_BASE 4U
1112#define COUNTERS_SIZE (1U << RADIX_BASE)
1113
1114static u8 get4bits(u64 num, int shift) {
1115 u8 low4bits;
1116
1117 num >>= shift;
1118 /* Reverse order */
1119 low4bits = (COUNTERS_SIZE - 1) - (num % COUNTERS_SIZE);
1120 return low4bits;
1121}
1122
1123/*
1124 * Use 4 bits as radix base
1125 * Use 16 u32 counters for calculating new position in buf array
1126 *
1127 * @array - array that will be sorted
1128 * @array_buf - buffer array to store sorting results
1129 * must be equal in size to @array
1130 * @num - array size
1131 */
1132static void radix_sort(struct bucket_item *array, struct bucket_item *array_buf,
1133 int num)
1134{
1135 u64 max_num;
1136 u64 buf_num;
1137 u32 counters[COUNTERS_SIZE];
1138 u32 new_addr;
1139 u32 addr;
1140 int bitlen;
1141 int shift;
1142 int i;
1143
1144 /*
1145 * Try avoid useless loop iterations for small numbers stored in big
1146 * counters. Example: 48 33 4 ... in 64bit array
1147 */
1148 max_num = array[0].count;
1149 for (i = 1; i < num; i++) {
1150 buf_num = array[i].count;
1151 if (buf_num > max_num)
1152 max_num = buf_num;
1153 }
1154
1155 buf_num = ilog2(max_num);
1156 bitlen = ALIGN(buf_num, RADIX_BASE * 2);
1157
1158 shift = 0;
1159 while (shift < bitlen) {
1160 memset(counters, 0, sizeof(counters));
1161
1162 for (i = 0; i < num; i++) {
1163 buf_num = array[i].count;
1164 addr = get4bits(num: buf_num, shift);
1165 counters[addr]++;
1166 }
1167
1168 for (i = 1; i < COUNTERS_SIZE; i++)
1169 counters[i] += counters[i - 1];
1170
1171 for (i = num - 1; i >= 0; i--) {
1172 buf_num = array[i].count;
1173 addr = get4bits(num: buf_num, shift);
1174 counters[addr]--;
1175 new_addr = counters[addr];
1176 array_buf[new_addr] = array[i];
1177 }
1178
1179 shift += RADIX_BASE;
1180
1181 /*
1182 * Normal radix expects to move data from a temporary array, to
1183 * the main one. But that requires some CPU time. Avoid that
1184 * by doing another sort iteration to original array instead of
1185 * memcpy()
1186 */
1187 memset(counters, 0, sizeof(counters));
1188
1189 for (i = 0; i < num; i ++) {
1190 buf_num = array_buf[i].count;
1191 addr = get4bits(num: buf_num, shift);
1192 counters[addr]++;
1193 }
1194
1195 for (i = 1; i < COUNTERS_SIZE; i++)
1196 counters[i] += counters[i - 1];
1197
1198 for (i = num - 1; i >= 0; i--) {
1199 buf_num = array_buf[i].count;
1200 addr = get4bits(num: buf_num, shift);
1201 counters[addr]--;
1202 new_addr = counters[addr];
1203 array[new_addr] = array_buf[i];
1204 }
1205
1206 shift += RADIX_BASE;
1207 }
1208}
1209
1210/*
1211 * Size of the core byte set - how many bytes cover 90% of the sample
1212 *
1213 * There are several types of structured binary data that use nearly all byte
1214 * values. The distribution can be uniform and counts in all buckets will be
1215 * nearly the same (eg. encrypted data). Unlikely to be compressible.
1216 *
1217 * Other possibility is normal (Gaussian) distribution, where the data could
1218 * be potentially compressible, but we have to take a few more steps to decide
1219 * how much.
1220 *
1221 * @BYTE_CORE_SET_LOW - main part of byte values repeated frequently,
1222 * compression algo can easy fix that
1223 * @BYTE_CORE_SET_HIGH - data have uniform distribution and with high
1224 * probability is not compressible
1225 */
1226#define BYTE_CORE_SET_LOW (64)
1227#define BYTE_CORE_SET_HIGH (200)
1228
1229static int byte_core_set_size(struct heuristic_ws *ws)
1230{
1231 u32 i;
1232 u32 coreset_sum = 0;
1233 const u32 core_set_threshold = ws->sample_size * 90 / 100;
1234 struct bucket_item *bucket = ws->bucket;
1235
1236 /* Sort in reverse order */
1237 radix_sort(array: ws->bucket, array_buf: ws->bucket_b, BUCKET_SIZE);
1238
1239 for (i = 0; i < BYTE_CORE_SET_LOW; i++)
1240 coreset_sum += bucket[i].count;
1241
1242 if (coreset_sum > core_set_threshold)
1243 return i;
1244
1245 for (; i < BYTE_CORE_SET_HIGH && bucket[i].count > 0; i++) {
1246 coreset_sum += bucket[i].count;
1247 if (coreset_sum > core_set_threshold)
1248 break;
1249 }
1250
1251 return i;
1252}
1253
1254/*
1255 * Count byte values in buckets.
1256 * This heuristic can detect textual data (configs, xml, json, html, etc).
1257 * Because in most text-like data byte set is restricted to limited number of
1258 * possible characters, and that restriction in most cases makes data easy to
1259 * compress.
1260 *
1261 * @BYTE_SET_THRESHOLD - consider all data within this byte set size:
1262 * less - compressible
1263 * more - need additional analysis
1264 */
1265#define BYTE_SET_THRESHOLD (64)
1266
1267static u32 byte_set_size(const struct heuristic_ws *ws)
1268{
1269 u32 i;
1270 u32 byte_set_size = 0;
1271
1272 for (i = 0; i < BYTE_SET_THRESHOLD; i++) {
1273 if (ws->bucket[i].count > 0)
1274 byte_set_size++;
1275 }
1276
1277 /*
1278 * Continue collecting count of byte values in buckets. If the byte
1279 * set size is bigger then the threshold, it's pointless to continue,
1280 * the detection technique would fail for this type of data.
1281 */
1282 for (; i < BUCKET_SIZE; i++) {
1283 if (ws->bucket[i].count > 0) {
1284 byte_set_size++;
1285 if (byte_set_size > BYTE_SET_THRESHOLD)
1286 return byte_set_size;
1287 }
1288 }
1289
1290 return byte_set_size;
1291}
1292
1293static bool sample_repeated_patterns(struct heuristic_ws *ws)
1294{
1295 const u32 half_of_sample = ws->sample_size / 2;
1296 const u8 *data = ws->sample;
1297
1298 return memcmp(p: &data[0], q: &data[half_of_sample], size: half_of_sample) == 0;
1299}
1300
1301static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end,
1302 struct heuristic_ws *ws)
1303{
1304 struct page *page;
1305 u64 index, index_end;
1306 u32 i, curr_sample_pos;
1307 u8 *in_data;
1308
1309 /*
1310 * Compression handles the input data by chunks of 128KiB
1311 * (defined by BTRFS_MAX_UNCOMPRESSED)
1312 *
1313 * We do the same for the heuristic and loop over the whole range.
1314 *
1315 * MAX_SAMPLE_SIZE - calculated under assumption that heuristic will
1316 * process no more than BTRFS_MAX_UNCOMPRESSED at a time.
1317 */
1318 if (end - start > BTRFS_MAX_UNCOMPRESSED)
1319 end = start + BTRFS_MAX_UNCOMPRESSED;
1320
1321 index = start >> PAGE_SHIFT;
1322 index_end = end >> PAGE_SHIFT;
1323
1324 /* Don't miss unaligned end */
1325 if (!PAGE_ALIGNED(end))
1326 index_end++;
1327
1328 curr_sample_pos = 0;
1329 while (index < index_end) {
1330 page = find_get_page(mapping: inode->i_mapping, offset: index);
1331 in_data = kmap_local_page(page);
1332 /* Handle case where the start is not aligned to PAGE_SIZE */
1333 i = start % PAGE_SIZE;
1334 while (i < PAGE_SIZE - SAMPLING_READ_SIZE) {
1335 /* Don't sample any garbage from the last page */
1336 if (start > end - SAMPLING_READ_SIZE)
1337 break;
1338 memcpy(&ws->sample[curr_sample_pos], &in_data[i],
1339 SAMPLING_READ_SIZE);
1340 i += SAMPLING_INTERVAL;
1341 start += SAMPLING_INTERVAL;
1342 curr_sample_pos += SAMPLING_READ_SIZE;
1343 }
1344 kunmap_local(in_data);
1345 put_page(page);
1346
1347 index++;
1348 }
1349
1350 ws->sample_size = curr_sample_pos;
1351}
1352
1353/*
1354 * Compression heuristic.
1355 *
1356 * For now is's a naive and optimistic 'return true', we'll extend the logic to
1357 * quickly (compared to direct compression) detect data characteristics
1358 * (compressible/incompressible) to avoid wasting CPU time on incompressible
1359 * data.
1360 *
1361 * The following types of analysis can be performed:
1362 * - detect mostly zero data
1363 * - detect data with low "byte set" size (text, etc)
1364 * - detect data with low/high "core byte" set
1365 *
1366 * Return non-zero if the compression should be done, 0 otherwise.
1367 */
1368int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
1369{
1370 struct list_head *ws_list = get_workspace(type: 0, level: 0);
1371 struct heuristic_ws *ws;
1372 u32 i;
1373 u8 byte;
1374 int ret = 0;
1375
1376 ws = list_entry(ws_list, struct heuristic_ws, list);
1377
1378 heuristic_collect_sample(inode, start, end, ws);
1379
1380 if (sample_repeated_patterns(ws)) {
1381 ret = 1;
1382 goto out;
1383 }
1384
1385 memset(ws->bucket, 0, sizeof(*ws->bucket)*BUCKET_SIZE);
1386
1387 for (i = 0; i < ws->sample_size; i++) {
1388 byte = ws->sample[i];
1389 ws->bucket[byte].count++;
1390 }
1391
1392 i = byte_set_size(ws);
1393 if (i < BYTE_SET_THRESHOLD) {
1394 ret = 2;
1395 goto out;
1396 }
1397
1398 i = byte_core_set_size(ws);
1399 if (i <= BYTE_CORE_SET_LOW) {
1400 ret = 3;
1401 goto out;
1402 }
1403
1404 if (i >= BYTE_CORE_SET_HIGH) {
1405 ret = 0;
1406 goto out;
1407 }
1408
1409 i = shannon_entropy(ws);
1410 if (i <= ENTROPY_LVL_ACEPTABLE) {
1411 ret = 4;
1412 goto out;
1413 }
1414
1415 /*
1416 * For the levels below ENTROPY_LVL_HIGH, additional analysis would be
1417 * needed to give green light to compression.
1418 *
1419 * For now just assume that compression at that level is not worth the
1420 * resources because:
1421 *
1422 * 1. it is possible to defrag the data later
1423 *
1424 * 2. the data would turn out to be hardly compressible, eg. 150 byte
1425 * values, every bucket has counter at level ~54. The heuristic would
1426 * be confused. This can happen when data have some internal repeated
1427 * patterns like "abbacbbc...". This can be detected by analyzing
1428 * pairs of bytes, which is too costly.
1429 */
1430 if (i < ENTROPY_LVL_HIGH) {
1431 ret = 5;
1432 goto out;
1433 } else {
1434 ret = 0;
1435 goto out;
1436 }
1437
1438out:
1439 put_workspace(type: 0, ws: ws_list);
1440 return ret;
1441}
1442
1443/*
1444 * Convert the compression suffix (eg. after "zlib" starting with ":") to
1445 * level, unrecognized string will set the default level
1446 */
1447unsigned int btrfs_compress_str2level(unsigned int type, const char *str)
1448{
1449 unsigned int level = 0;
1450 int ret;
1451
1452 if (!type)
1453 return 0;
1454
1455 if (str[0] == ':') {
1456 ret = kstrtouint(s: str + 1, base: 10, res: &level);
1457 if (ret)
1458 level = 0;
1459 }
1460
1461 level = btrfs_compress_set_level(type, level);
1462
1463 return level;
1464}
1465

source code of linux/fs/btrfs/compression.c