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Linux/fs/btrfs/compression.c

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  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/buffer_head.h>
  9 #include <linux/file.h>
 10 #include <linux/fs.h>
 11 #include <linux/pagemap.h>
 12 #include <linux/highmem.h>
 13 #include <linux/time.h>
 14 #include <linux/init.h>
 15 #include <linux/string.h>
 16 #include <linux/backing-dev.h>
 17 #include <linux/mpage.h>
 18 #include <linux/swap.h>
 19 #include <linux/writeback.h>
 20 #include <linux/bit_spinlock.h>
 21 #include <linux/slab.h>
 22 #include <linux/sched/mm.h>
 23 #include <linux/log2.h>
 24 #include "ctree.h"
 25 #include "disk-io.h"
 26 #include "transaction.h"
 27 #include "btrfs_inode.h"
 28 #include "volumes.h"
 29 #include "ordered-data.h"
 30 #include "compression.h"
 31 #include "extent_io.h"
 32 #include "extent_map.h"
 33 
 34 static const char* const btrfs_compress_types[] = { "", "zlib", "lzo", "zstd" };
 35 
 36 const char* btrfs_compress_type2str(enum btrfs_compression_type type)
 37 {
 38         switch (type) {
 39         case BTRFS_COMPRESS_ZLIB:
 40         case BTRFS_COMPRESS_LZO:
 41         case BTRFS_COMPRESS_ZSTD:
 42         case BTRFS_COMPRESS_NONE:
 43                 return btrfs_compress_types[type];
 44         }
 45 
 46         return NULL;
 47 }
 48 
 49 static int btrfs_decompress_bio(struct compressed_bio *cb);
 50 
 51 static inline int compressed_bio_size(struct btrfs_fs_info *fs_info,
 52                                       unsigned long disk_size)
 53 {
 54         u16 csum_size = btrfs_super_csum_size(fs_info->super_copy);
 55 
 56         return sizeof(struct compressed_bio) +
 57                 (DIV_ROUND_UP(disk_size, fs_info->sectorsize)) * csum_size;
 58 }
 59 
 60 static int check_compressed_csum(struct btrfs_inode *inode,
 61                                  struct compressed_bio *cb,
 62                                  u64 disk_start)
 63 {
 64         int ret;
 65         struct page *page;
 66         unsigned long i;
 67         char *kaddr;
 68         u32 csum;
 69         u32 *cb_sum = &cb->sums;
 70 
 71         if (inode->flags & BTRFS_INODE_NODATASUM)
 72                 return 0;
 73 
 74         for (i = 0; i < cb->nr_pages; i++) {
 75                 page = cb->compressed_pages[i];
 76                 csum = ~(u32)0;
 77 
 78                 kaddr = kmap_atomic(page);
 79                 csum = btrfs_csum_data(kaddr, csum, PAGE_SIZE);
 80                 btrfs_csum_final(csum, (u8 *)&csum);
 81                 kunmap_atomic(kaddr);
 82 
 83                 if (csum != *cb_sum) {
 84                         btrfs_print_data_csum_error(inode, disk_start, csum,
 85                                         *cb_sum, cb->mirror_num);
 86                         ret = -EIO;
 87                         goto fail;
 88                 }
 89                 cb_sum++;
 90 
 91         }
 92         ret = 0;
 93 fail:
 94         return ret;
 95 }
 96 
 97 /* when we finish reading compressed pages from the disk, we
 98  * decompress them and then run the bio end_io routines on the
 99  * decompressed pages (in the inode address space).
100  *
101  * This allows the checksumming and other IO error handling routines
102  * to work normally
103  *
104  * The compressed pages are freed here, and it must be run
105  * in process context
106  */
107 static void end_compressed_bio_read(struct bio *bio)
108 {
109         struct compressed_bio *cb = bio->bi_private;
110         struct inode *inode;
111         struct page *page;
112         unsigned long index;
113         unsigned int mirror = btrfs_io_bio(bio)->mirror_num;
114         int ret = 0;
115 
116         if (bio->bi_status)
117                 cb->errors = 1;
118 
119         /* if there are more bios still pending for this compressed
120          * extent, just exit
121          */
122         if (!refcount_dec_and_test(&cb->pending_bios))
123                 goto out;
124 
125         /*
126          * Record the correct mirror_num in cb->orig_bio so that
127          * read-repair can work properly.
128          */
129         ASSERT(btrfs_io_bio(cb->orig_bio));
130         btrfs_io_bio(cb->orig_bio)->mirror_num = mirror;
131         cb->mirror_num = mirror;
132 
133         /*
134          * Some IO in this cb have failed, just skip checksum as there
135          * is no way it could be correct.
136          */
137         if (cb->errors == 1)
138                 goto csum_failed;
139 
140         inode = cb->inode;
141         ret = check_compressed_csum(BTRFS_I(inode), cb,
142                                     (u64)bio->bi_iter.bi_sector << 9);
143         if (ret)
144                 goto csum_failed;
145 
146         /* ok, we're the last bio for this extent, lets start
147          * the decompression.
148          */
149         ret = btrfs_decompress_bio(cb);
150 
151 csum_failed:
152         if (ret)
153                 cb->errors = 1;
154 
155         /* release the compressed pages */
156         index = 0;
157         for (index = 0; index < cb->nr_pages; index++) {
158                 page = cb->compressed_pages[index];
159                 page->mapping = NULL;
160                 put_page(page);
161         }
162 
163         /* do io completion on the original bio */
164         if (cb->errors) {
165                 bio_io_error(cb->orig_bio);
166         } else {
167                 int i;
168                 struct bio_vec *bvec;
169 
170                 /*
171                  * we have verified the checksum already, set page
172                  * checked so the end_io handlers know about it
173                  */
174                 ASSERT(!bio_flagged(bio, BIO_CLONED));
175                 bio_for_each_segment_all(bvec, cb->orig_bio, i)
176                         SetPageChecked(bvec->bv_page);
177 
178                 bio_endio(cb->orig_bio);
179         }
180 
181         /* finally free the cb struct */
182         kfree(cb->compressed_pages);
183         kfree(cb);
184 out:
185         bio_put(bio);
186 }
187 
188 /*
189  * Clear the writeback bits on all of the file
190  * pages for a compressed write
191  */
192 static noinline void end_compressed_writeback(struct inode *inode,
193                                               const struct compressed_bio *cb)
194 {
195         unsigned long index = cb->start >> PAGE_SHIFT;
196         unsigned long end_index = (cb->start + cb->len - 1) >> PAGE_SHIFT;
197         struct page *pages[16];
198         unsigned long nr_pages = end_index - index + 1;
199         int i;
200         int ret;
201 
202         if (cb->errors)
203                 mapping_set_error(inode->i_mapping, -EIO);
204 
205         while (nr_pages > 0) {
206                 ret = find_get_pages_contig(inode->i_mapping, index,
207                                      min_t(unsigned long,
208                                      nr_pages, ARRAY_SIZE(pages)), pages);
209                 if (ret == 0) {
210                         nr_pages -= 1;
211                         index += 1;
212                         continue;
213                 }
214                 for (i = 0; i < ret; i++) {
215                         if (cb->errors)
216                                 SetPageError(pages[i]);
217                         end_page_writeback(pages[i]);
218                         put_page(pages[i]);
219                 }
220                 nr_pages -= ret;
221                 index += ret;
222         }
223         /* the inode may be gone now */
224 }
225 
226 /*
227  * do the cleanup once all the compressed pages hit the disk.
228  * This will clear writeback on the file pages and free the compressed
229  * pages.
230  *
231  * This also calls the writeback end hooks for the file pages so that
232  * metadata and checksums can be updated in the file.
233  */
234 static void end_compressed_bio_write(struct bio *bio)
235 {
236         struct extent_io_tree *tree;
237         struct compressed_bio *cb = bio->bi_private;
238         struct inode *inode;
239         struct page *page;
240         unsigned long index;
241 
242         if (bio->bi_status)
243                 cb->errors = 1;
244 
245         /* if there are more bios still pending for this compressed
246          * extent, just exit
247          */
248         if (!refcount_dec_and_test(&cb->pending_bios))
249                 goto out;
250 
251         /* ok, we're the last bio for this extent, step one is to
252          * call back into the FS and do all the end_io operations
253          */
254         inode = cb->inode;
255         tree = &BTRFS_I(inode)->io_tree;
256         cb->compressed_pages[0]->mapping = cb->inode->i_mapping;
257         tree->ops->writepage_end_io_hook(cb->compressed_pages[0],
258                                          cb->start,
259                                          cb->start + cb->len - 1,
260                                          NULL,
261                                          bio->bi_status ?
262                                          BLK_STS_OK : BLK_STS_NOTSUPP);
263         cb->compressed_pages[0]->mapping = NULL;
264 
265         end_compressed_writeback(inode, cb);
266         /* note, our inode could be gone now */
267 
268         /*
269          * release the compressed pages, these came from alloc_page and
270          * are not attached to the inode at all
271          */
272         index = 0;
273         for (index = 0; index < cb->nr_pages; index++) {
274                 page = cb->compressed_pages[index];
275                 page->mapping = NULL;
276                 put_page(page);
277         }
278 
279         /* finally free the cb struct */
280         kfree(cb->compressed_pages);
281         kfree(cb);
282 out:
283         bio_put(bio);
284 }
285 
286 /*
287  * worker function to build and submit bios for previously compressed pages.
288  * The corresponding pages in the inode should be marked for writeback
289  * and the compressed pages should have a reference on them for dropping
290  * when the IO is complete.
291  *
292  * This also checksums the file bytes and gets things ready for
293  * the end io hooks.
294  */
295 blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
296                                  unsigned long len, u64 disk_start,
297                                  unsigned long compressed_len,
298                                  struct page **compressed_pages,
299                                  unsigned long nr_pages,
300                                  unsigned int write_flags)
301 {
302         struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
303         struct bio *bio = NULL;
304         struct compressed_bio *cb;
305         unsigned long bytes_left;
306         struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
307         int pg_index = 0;
308         struct page *page;
309         u64 first_byte = disk_start;
310         struct block_device *bdev;
311         blk_status_t ret;
312         int skip_sum = BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM;
313 
314         WARN_ON(start & ((u64)PAGE_SIZE - 1));
315         cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS);
316         if (!cb)
317                 return BLK_STS_RESOURCE;
318         refcount_set(&cb->pending_bios, 0);
319         cb->errors = 0;
320         cb->inode = inode;
321         cb->start = start;
322         cb->len = len;
323         cb->mirror_num = 0;
324         cb->compressed_pages = compressed_pages;
325         cb->compressed_len = compressed_len;
326         cb->orig_bio = NULL;
327         cb->nr_pages = nr_pages;
328 
329         bdev = fs_info->fs_devices->latest_bdev;
330 
331         bio = btrfs_bio_alloc(bdev, first_byte);
332         bio->bi_opf = REQ_OP_WRITE | write_flags;
333         bio->bi_private = cb;
334         bio->bi_end_io = end_compressed_bio_write;
335         refcount_set(&cb->pending_bios, 1);
336 
337         /* create and submit bios for the compressed pages */
338         bytes_left = compressed_len;
339         for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
340                 int submit = 0;
341 
342                 page = compressed_pages[pg_index];
343                 page->mapping = inode->i_mapping;
344                 if (bio->bi_iter.bi_size)
345                         submit = io_tree->ops->merge_bio_hook(page, 0,
346                                                            PAGE_SIZE,
347                                                            bio, 0);
348 
349                 page->mapping = NULL;
350                 if (submit || bio_add_page(bio, page, PAGE_SIZE, 0) <
351                     PAGE_SIZE) {
352                         /*
353                          * inc the count before we submit the bio so
354                          * we know the end IO handler won't happen before
355                          * we inc the count.  Otherwise, the cb might get
356                          * freed before we're done setting it up
357                          */
358                         refcount_inc(&cb->pending_bios);
359                         ret = btrfs_bio_wq_end_io(fs_info, bio,
360                                                   BTRFS_WQ_ENDIO_DATA);
361                         BUG_ON(ret); /* -ENOMEM */
362 
363                         if (!skip_sum) {
364                                 ret = btrfs_csum_one_bio(inode, bio, start, 1);
365                                 BUG_ON(ret); /* -ENOMEM */
366                         }
367 
368                         ret = btrfs_map_bio(fs_info, bio, 0, 1);
369                         if (ret) {
370                                 bio->bi_status = ret;
371                                 bio_endio(bio);
372                         }
373 
374                         bio = btrfs_bio_alloc(bdev, first_byte);
375                         bio->bi_opf = REQ_OP_WRITE | write_flags;
376                         bio->bi_private = cb;
377                         bio->bi_end_io = end_compressed_bio_write;
378                         bio_add_page(bio, page, PAGE_SIZE, 0);
379                 }
380                 if (bytes_left < PAGE_SIZE) {
381                         btrfs_info(fs_info,
382                                         "bytes left %lu compress len %lu nr %lu",
383                                bytes_left, cb->compressed_len, cb->nr_pages);
384                 }
385                 bytes_left -= PAGE_SIZE;
386                 first_byte += PAGE_SIZE;
387                 cond_resched();
388         }
389 
390         ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA);
391         BUG_ON(ret); /* -ENOMEM */
392 
393         if (!skip_sum) {
394                 ret = btrfs_csum_one_bio(inode, bio, start, 1);
395                 BUG_ON(ret); /* -ENOMEM */
396         }
397 
398         ret = btrfs_map_bio(fs_info, bio, 0, 1);
399         if (ret) {
400                 bio->bi_status = ret;
401                 bio_endio(bio);
402         }
403 
404         return 0;
405 }
406 
407 static u64 bio_end_offset(struct bio *bio)
408 {
409         struct bio_vec *last = bio_last_bvec_all(bio);
410 
411         return page_offset(last->bv_page) + last->bv_len + last->bv_offset;
412 }
413 
414 static noinline int add_ra_bio_pages(struct inode *inode,
415                                      u64 compressed_end,
416                                      struct compressed_bio *cb)
417 {
418         unsigned long end_index;
419         unsigned long pg_index;
420         u64 last_offset;
421         u64 isize = i_size_read(inode);
422         int ret;
423         struct page *page;
424         unsigned long nr_pages = 0;
425         struct extent_map *em;
426         struct address_space *mapping = inode->i_mapping;
427         struct extent_map_tree *em_tree;
428         struct extent_io_tree *tree;
429         u64 end;
430         int misses = 0;
431 
432         last_offset = bio_end_offset(cb->orig_bio);
433         em_tree = &BTRFS_I(inode)->extent_tree;
434         tree = &BTRFS_I(inode)->io_tree;
435 
436         if (isize == 0)
437                 return 0;
438 
439         end_index = (i_size_read(inode) - 1) >> PAGE_SHIFT;
440 
441         while (last_offset < compressed_end) {
442                 pg_index = last_offset >> PAGE_SHIFT;
443 
444                 if (pg_index > end_index)
445                         break;
446 
447                 rcu_read_lock();
448                 page = radix_tree_lookup(&mapping->i_pages, pg_index);
449                 rcu_read_unlock();
450                 if (page && !radix_tree_exceptional_entry(page)) {
451                         misses++;
452                         if (misses > 4)
453                                 break;
454                         goto next;
455                 }
456 
457                 page = __page_cache_alloc(mapping_gfp_constraint(mapping,
458                                                                  ~__GFP_FS));
459                 if (!page)
460                         break;
461 
462                 if (add_to_page_cache_lru(page, mapping, pg_index, GFP_NOFS)) {
463                         put_page(page);
464                         goto next;
465                 }
466 
467                 end = last_offset + PAGE_SIZE - 1;
468                 /*
469                  * at this point, we have a locked page in the page cache
470                  * for these bytes in the file.  But, we have to make
471                  * sure they map to this compressed extent on disk.
472                  */
473                 set_page_extent_mapped(page);
474                 lock_extent(tree, last_offset, end);
475                 read_lock(&em_tree->lock);
476                 em = lookup_extent_mapping(em_tree, last_offset,
477                                            PAGE_SIZE);
478                 read_unlock(&em_tree->lock);
479 
480                 if (!em || last_offset < em->start ||
481                     (last_offset + PAGE_SIZE > extent_map_end(em)) ||
482                     (em->block_start >> 9) != cb->orig_bio->bi_iter.bi_sector) {
483                         free_extent_map(em);
484                         unlock_extent(tree, last_offset, end);
485                         unlock_page(page);
486                         put_page(page);
487                         break;
488                 }
489                 free_extent_map(em);
490 
491                 if (page->index == end_index) {
492                         char *userpage;
493                         size_t zero_offset = isize & (PAGE_SIZE - 1);
494 
495                         if (zero_offset) {
496                                 int zeros;
497                                 zeros = PAGE_SIZE - zero_offset;
498                                 userpage = kmap_atomic(page);
499                                 memset(userpage + zero_offset, 0, zeros);
500                                 flush_dcache_page(page);
501                                 kunmap_atomic(userpage);
502                         }
503                 }
504 
505                 ret = bio_add_page(cb->orig_bio, page,
506                                    PAGE_SIZE, 0);
507 
508                 if (ret == PAGE_SIZE) {
509                         nr_pages++;
510                         put_page(page);
511                 } else {
512                         unlock_extent(tree, last_offset, end);
513                         unlock_page(page);
514                         put_page(page);
515                         break;
516                 }
517 next:
518                 last_offset += PAGE_SIZE;
519         }
520         return 0;
521 }
522 
523 /*
524  * for a compressed read, the bio we get passed has all the inode pages
525  * in it.  We don't actually do IO on those pages but allocate new ones
526  * to hold the compressed pages on disk.
527  *
528  * bio->bi_iter.bi_sector points to the compressed extent on disk
529  * bio->bi_io_vec points to all of the inode pages
530  *
531  * After the compressed pages are read, we copy the bytes into the
532  * bio we were passed and then call the bio end_io calls
533  */
534 blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
535                                  int mirror_num, unsigned long bio_flags)
536 {
537         struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
538         struct extent_io_tree *tree;
539         struct extent_map_tree *em_tree;
540         struct compressed_bio *cb;
541         unsigned long compressed_len;
542         unsigned long nr_pages;
543         unsigned long pg_index;
544         struct page *page;
545         struct block_device *bdev;
546         struct bio *comp_bio;
547         u64 cur_disk_byte = (u64)bio->bi_iter.bi_sector << 9;
548         u64 em_len;
549         u64 em_start;
550         struct extent_map *em;
551         blk_status_t ret = BLK_STS_RESOURCE;
552         int faili = 0;
553         u32 *sums;
554 
555         tree = &BTRFS_I(inode)->io_tree;
556         em_tree = &BTRFS_I(inode)->extent_tree;
557 
558         /* we need the actual starting offset of this extent in the file */
559         read_lock(&em_tree->lock);
560         em = lookup_extent_mapping(em_tree,
561                                    page_offset(bio_first_page_all(bio)),
562                                    PAGE_SIZE);
563         read_unlock(&em_tree->lock);
564         if (!em)
565                 return BLK_STS_IOERR;
566 
567         compressed_len = em->block_len;
568         cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS);
569         if (!cb)
570                 goto out;
571 
572         refcount_set(&cb->pending_bios, 0);
573         cb->errors = 0;
574         cb->inode = inode;
575         cb->mirror_num = mirror_num;
576         sums = &cb->sums;
577 
578         cb->start = em->orig_start;
579         em_len = em->len;
580         em_start = em->start;
581 
582         free_extent_map(em);
583         em = NULL;
584 
585         cb->len = bio->bi_iter.bi_size;
586         cb->compressed_len = compressed_len;
587         cb->compress_type = extent_compress_type(bio_flags);
588         cb->orig_bio = bio;
589 
590         nr_pages = DIV_ROUND_UP(compressed_len, PAGE_SIZE);
591         cb->compressed_pages = kcalloc(nr_pages, sizeof(struct page *),
592                                        GFP_NOFS);
593         if (!cb->compressed_pages)
594                 goto fail1;
595 
596         bdev = fs_info->fs_devices->latest_bdev;
597 
598         for (pg_index = 0; pg_index < nr_pages; pg_index++) {
599                 cb->compressed_pages[pg_index] = alloc_page(GFP_NOFS |
600                                                               __GFP_HIGHMEM);
601                 if (!cb->compressed_pages[pg_index]) {
602                         faili = pg_index - 1;
603                         ret = BLK_STS_RESOURCE;
604                         goto fail2;
605                 }
606         }
607         faili = nr_pages - 1;
608         cb->nr_pages = nr_pages;
609 
610         add_ra_bio_pages(inode, em_start + em_len, cb);
611 
612         /* include any pages we added in add_ra-bio_pages */
613         cb->len = bio->bi_iter.bi_size;
614 
615         comp_bio = btrfs_bio_alloc(bdev, cur_disk_byte);
616         bio_set_op_attrs (comp_bio, REQ_OP_READ, 0);
617         comp_bio->bi_private = cb;
618         comp_bio->bi_end_io = end_compressed_bio_read;
619         refcount_set(&cb->pending_bios, 1);
620 
621         for (pg_index = 0; pg_index < nr_pages; pg_index++) {
622                 int submit = 0;
623 
624                 page = cb->compressed_pages[pg_index];
625                 page->mapping = inode->i_mapping;
626                 page->index = em_start >> PAGE_SHIFT;
627 
628                 if (comp_bio->bi_iter.bi_size)
629                         submit = tree->ops->merge_bio_hook(page, 0,
630                                                         PAGE_SIZE,
631                                                         comp_bio, 0);
632 
633                 page->mapping = NULL;
634                 if (submit || bio_add_page(comp_bio, page, PAGE_SIZE, 0) <
635                     PAGE_SIZE) {
636                         ret = btrfs_bio_wq_end_io(fs_info, comp_bio,
637                                                   BTRFS_WQ_ENDIO_DATA);
638                         BUG_ON(ret); /* -ENOMEM */
639 
640                         /*
641                          * inc the count before we submit the bio so
642                          * we know the end IO handler won't happen before
643                          * we inc the count.  Otherwise, the cb might get
644                          * freed before we're done setting it up
645                          */
646                         refcount_inc(&cb->pending_bios);
647 
648                         if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
649                                 ret = btrfs_lookup_bio_sums(inode, comp_bio,
650                                                             sums);
651                                 BUG_ON(ret); /* -ENOMEM */
652                         }
653                         sums += DIV_ROUND_UP(comp_bio->bi_iter.bi_size,
654                                              fs_info->sectorsize);
655 
656                         ret = btrfs_map_bio(fs_info, comp_bio, mirror_num, 0);
657                         if (ret) {
658                                 comp_bio->bi_status = ret;
659                                 bio_endio(comp_bio);
660                         }
661 
662                         comp_bio = btrfs_bio_alloc(bdev, cur_disk_byte);
663                         bio_set_op_attrs(comp_bio, REQ_OP_READ, 0);
664                         comp_bio->bi_private = cb;
665                         comp_bio->bi_end_io = end_compressed_bio_read;
666 
667                         bio_add_page(comp_bio, page, PAGE_SIZE, 0);
668                 }
669                 cur_disk_byte += PAGE_SIZE;
670         }
671 
672         ret = btrfs_bio_wq_end_io(fs_info, comp_bio, BTRFS_WQ_ENDIO_DATA);
673         BUG_ON(ret); /* -ENOMEM */
674 
675         if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
676                 ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
677                 BUG_ON(ret); /* -ENOMEM */
678         }
679 
680         ret = btrfs_map_bio(fs_info, comp_bio, mirror_num, 0);
681         if (ret) {
682                 comp_bio->bi_status = ret;
683                 bio_endio(comp_bio);
684         }
685 
686         return 0;
687 
688 fail2:
689         while (faili >= 0) {
690                 __free_page(cb->compressed_pages[faili]);
691                 faili--;
692         }
693 
694         kfree(cb->compressed_pages);
695 fail1:
696         kfree(cb);
697 out:
698         free_extent_map(em);
699         return ret;
700 }
701 
702 /*
703  * Heuristic uses systematic sampling to collect data from the input data
704  * range, the logic can be tuned by the following constants:
705  *
706  * @SAMPLING_READ_SIZE - how many bytes will be copied from for each sample
707  * @SAMPLING_INTERVAL  - range from which the sampled data can be collected
708  */
709 #define SAMPLING_READ_SIZE      (16)
710 #define SAMPLING_INTERVAL       (256)
711 
712 /*
713  * For statistical analysis of the input data we consider bytes that form a
714  * Galois Field of 256 objects. Each object has an attribute count, ie. how
715  * many times the object appeared in the sample.
716  */
717 #define BUCKET_SIZE             (256)
718 
719 /*
720  * The size of the sample is based on a statistical sampling rule of thumb.
721  * The common way is to perform sampling tests as long as the number of
722  * elements in each cell is at least 5.
723  *
724  * Instead of 5, we choose 32 to obtain more accurate results.
725  * If the data contain the maximum number of symbols, which is 256, we obtain a
726  * sample size bound by 8192.
727  *
728  * For a sample of at most 8KB of data per data range: 16 consecutive bytes
729  * from up to 512 locations.
730  */
731 #define MAX_SAMPLE_SIZE         (BTRFS_MAX_UNCOMPRESSED *               \
732                                  SAMPLING_READ_SIZE / SAMPLING_INTERVAL)
733 
734 struct bucket_item {
735         u32 count;
736 };
737 
738 struct heuristic_ws {
739         /* Partial copy of input data */
740         u8 *sample;
741         u32 sample_size;
742         /* Buckets store counters for each byte value */
743         struct bucket_item *bucket;
744         /* Sorting buffer */
745         struct bucket_item *bucket_b;
746         struct list_head list;
747 };
748 
749 static void free_heuristic_ws(struct list_head *ws)
750 {
751         struct heuristic_ws *workspace;
752 
753         workspace = list_entry(ws, struct heuristic_ws, list);
754 
755         kvfree(workspace->sample);
756         kfree(workspace->bucket);
757         kfree(workspace->bucket_b);
758         kfree(workspace);
759 }
760 
761 static struct list_head *alloc_heuristic_ws(void)
762 {
763         struct heuristic_ws *ws;
764 
765         ws = kzalloc(sizeof(*ws), GFP_KERNEL);
766         if (!ws)
767                 return ERR_PTR(-ENOMEM);
768 
769         ws->sample = kvmalloc(MAX_SAMPLE_SIZE, GFP_KERNEL);
770         if (!ws->sample)
771                 goto fail;
772 
773         ws->bucket = kcalloc(BUCKET_SIZE, sizeof(*ws->bucket), GFP_KERNEL);
774         if (!ws->bucket)
775                 goto fail;
776 
777         ws->bucket_b = kcalloc(BUCKET_SIZE, sizeof(*ws->bucket_b), GFP_KERNEL);
778         if (!ws->bucket_b)
779                 goto fail;
780 
781         INIT_LIST_HEAD(&ws->list);
782         return &ws->list;
783 fail:
784         free_heuristic_ws(&ws->list);
785         return ERR_PTR(-ENOMEM);
786 }
787 
788 struct workspaces_list {
789         struct list_head idle_ws;
790         spinlock_t ws_lock;
791         /* Number of free workspaces */
792         int free_ws;
793         /* Total number of allocated workspaces */
794         atomic_t total_ws;
795         /* Waiters for a free workspace */
796         wait_queue_head_t ws_wait;
797 };
798 
799 static struct workspaces_list btrfs_comp_ws[BTRFS_COMPRESS_TYPES];
800 
801 static struct workspaces_list btrfs_heuristic_ws;
802 
803 static const struct btrfs_compress_op * const btrfs_compress_op[] = {
804         &btrfs_zlib_compress,
805         &btrfs_lzo_compress,
806         &btrfs_zstd_compress,
807 };
808 
809 void __init btrfs_init_compress(void)
810 {
811         struct list_head *workspace;
812         int i;
813 
814         INIT_LIST_HEAD(&btrfs_heuristic_ws.idle_ws);
815         spin_lock_init(&btrfs_heuristic_ws.ws_lock);
816         atomic_set(&btrfs_heuristic_ws.total_ws, 0);
817         init_waitqueue_head(&btrfs_heuristic_ws.ws_wait);
818 
819         workspace = alloc_heuristic_ws();
820         if (IS_ERR(workspace)) {
821                 pr_warn(
822         "BTRFS: cannot preallocate heuristic workspace, will try later\n");
823         } else {
824                 atomic_set(&btrfs_heuristic_ws.total_ws, 1);
825                 btrfs_heuristic_ws.free_ws = 1;
826                 list_add(workspace, &btrfs_heuristic_ws.idle_ws);
827         }
828 
829         for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
830                 INIT_LIST_HEAD(&btrfs_comp_ws[i].idle_ws);
831                 spin_lock_init(&btrfs_comp_ws[i].ws_lock);
832                 atomic_set(&btrfs_comp_ws[i].total_ws, 0);
833                 init_waitqueue_head(&btrfs_comp_ws[i].ws_wait);
834 
835                 /*
836                  * Preallocate one workspace for each compression type so
837                  * we can guarantee forward progress in the worst case
838                  */
839                 workspace = btrfs_compress_op[i]->alloc_workspace();
840                 if (IS_ERR(workspace)) {
841                         pr_warn("BTRFS: cannot preallocate compression workspace, will try later\n");
842                 } else {
843                         atomic_set(&btrfs_comp_ws[i].total_ws, 1);
844                         btrfs_comp_ws[i].free_ws = 1;
845                         list_add(workspace, &btrfs_comp_ws[i].idle_ws);
846                 }
847         }
848 }
849 
850 /*
851  * This finds an available workspace or allocates a new one.
852  * If it's not possible to allocate a new one, waits until there's one.
853  * Preallocation makes a forward progress guarantees and we do not return
854  * errors.
855  */
856 static struct list_head *__find_workspace(int type, bool heuristic)
857 {
858         struct list_head *workspace;
859         int cpus = num_online_cpus();
860         int idx = type - 1;
861         unsigned nofs_flag;
862         struct list_head *idle_ws;
863         spinlock_t *ws_lock;
864         atomic_t *total_ws;
865         wait_queue_head_t *ws_wait;
866         int *free_ws;
867 
868         if (heuristic) {
869                 idle_ws  = &btrfs_heuristic_ws.idle_ws;
870                 ws_lock  = &btrfs_heuristic_ws.ws_lock;
871                 total_ws = &btrfs_heuristic_ws.total_ws;
872                 ws_wait  = &btrfs_heuristic_ws.ws_wait;
873                 free_ws  = &btrfs_heuristic_ws.free_ws;
874         } else {
875                 idle_ws  = &btrfs_comp_ws[idx].idle_ws;
876                 ws_lock  = &btrfs_comp_ws[idx].ws_lock;
877                 total_ws = &btrfs_comp_ws[idx].total_ws;
878                 ws_wait  = &btrfs_comp_ws[idx].ws_wait;
879                 free_ws  = &btrfs_comp_ws[idx].free_ws;
880         }
881 
882 again:
883         spin_lock(ws_lock);
884         if (!list_empty(idle_ws)) {
885                 workspace = idle_ws->next;
886                 list_del(workspace);
887                 (*free_ws)--;
888                 spin_unlock(ws_lock);
889                 return workspace;
890 
891         }
892         if (atomic_read(total_ws) > cpus) {
893                 DEFINE_WAIT(wait);
894 
895                 spin_unlock(ws_lock);
896                 prepare_to_wait(ws_wait, &wait, TASK_UNINTERRUPTIBLE);
897                 if (atomic_read(total_ws) > cpus && !*free_ws)
898                         schedule();
899                 finish_wait(ws_wait, &wait);
900                 goto again;
901         }
902         atomic_inc(total_ws);
903         spin_unlock(ws_lock);
904 
905         /*
906          * Allocation helpers call vmalloc that can't use GFP_NOFS, so we have
907          * to turn it off here because we might get called from the restricted
908          * context of btrfs_compress_bio/btrfs_compress_pages
909          */
910         nofs_flag = memalloc_nofs_save();
911         if (heuristic)
912                 workspace = alloc_heuristic_ws();
913         else
914                 workspace = btrfs_compress_op[idx]->alloc_workspace();
915         memalloc_nofs_restore(nofs_flag);
916 
917         if (IS_ERR(workspace)) {
918                 atomic_dec(total_ws);
919                 wake_up(ws_wait);
920 
921                 /*
922                  * Do not return the error but go back to waiting. There's a
923                  * workspace preallocated for each type and the compression
924                  * time is bounded so we get to a workspace eventually. This
925                  * makes our caller's life easier.
926                  *
927                  * To prevent silent and low-probability deadlocks (when the
928                  * initial preallocation fails), check if there are any
929                  * workspaces at all.
930                  */
931                 if (atomic_read(total_ws) == 0) {
932                         static DEFINE_RATELIMIT_STATE(_rs,
933                                         /* once per minute */ 60 * HZ,
934                                         /* no burst */ 1);
935 
936                         if (__ratelimit(&_rs)) {
937                                 pr_warn("BTRFS: no compression workspaces, low memory, retrying\n");
938                         }
939                 }
940                 goto again;
941         }
942         return workspace;
943 }
944 
945 static struct list_head *find_workspace(int type)
946 {
947         return __find_workspace(type, false);
948 }
949 
950 /*
951  * put a workspace struct back on the list or free it if we have enough
952  * idle ones sitting around
953  */
954 static void __free_workspace(int type, struct list_head *workspace,
955                              bool heuristic)
956 {
957         int idx = type - 1;
958         struct list_head *idle_ws;
959         spinlock_t *ws_lock;
960         atomic_t *total_ws;
961         wait_queue_head_t *ws_wait;
962         int *free_ws;
963 
964         if (heuristic) {
965                 idle_ws  = &btrfs_heuristic_ws.idle_ws;
966                 ws_lock  = &btrfs_heuristic_ws.ws_lock;
967                 total_ws = &btrfs_heuristic_ws.total_ws;
968                 ws_wait  = &btrfs_heuristic_ws.ws_wait;
969                 free_ws  = &btrfs_heuristic_ws.free_ws;
970         } else {
971                 idle_ws  = &btrfs_comp_ws[idx].idle_ws;
972                 ws_lock  = &btrfs_comp_ws[idx].ws_lock;
973                 total_ws = &btrfs_comp_ws[idx].total_ws;
974                 ws_wait  = &btrfs_comp_ws[idx].ws_wait;
975                 free_ws  = &btrfs_comp_ws[idx].free_ws;
976         }
977 
978         spin_lock(ws_lock);
979         if (*free_ws <= num_online_cpus()) {
980                 list_add(workspace, idle_ws);
981                 (*free_ws)++;
982                 spin_unlock(ws_lock);
983                 goto wake;
984         }
985         spin_unlock(ws_lock);
986 
987         if (heuristic)
988                 free_heuristic_ws(workspace);
989         else
990                 btrfs_compress_op[idx]->free_workspace(workspace);
991         atomic_dec(total_ws);
992 wake:
993         /*
994          * Make sure counter is updated before we wake up waiters.
995          */
996         smp_mb();
997         if (waitqueue_active(ws_wait))
998                 wake_up(ws_wait);
999 }
1000 
1001 static void free_workspace(int type, struct list_head *ws)
1002 {
1003         return __free_workspace(type, ws, false);
1004 }
1005 
1006 /*
1007  * cleanup function for module exit
1008  */
1009 static void free_workspaces(void)
1010 {
1011         struct list_head *workspace;
1012         int i;
1013 
1014         while (!list_empty(&btrfs_heuristic_ws.idle_ws)) {
1015                 workspace = btrfs_heuristic_ws.idle_ws.next;
1016                 list_del(workspace);
1017                 free_heuristic_ws(workspace);
1018                 atomic_dec(&btrfs_heuristic_ws.total_ws);
1019         }
1020 
1021         for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
1022                 while (!list_empty(&btrfs_comp_ws[i].idle_ws)) {
1023                         workspace = btrfs_comp_ws[i].idle_ws.next;
1024                         list_del(workspace);
1025                         btrfs_compress_op[i]->free_workspace(workspace);
1026                         atomic_dec(&btrfs_comp_ws[i].total_ws);
1027                 }
1028         }
1029 }
1030 
1031 /*
1032  * Given an address space and start and length, compress the bytes into @pages
1033  * that are allocated on demand.
1034  *
1035  * @type_level is encoded algorithm and level, where level 0 means whatever
1036  * default the algorithm chooses and is opaque here;
1037  * - compression algo are 0-3
1038  * - the level are bits 4-7
1039  *
1040  * @out_pages is an in/out parameter, holds maximum number of pages to allocate
1041  * and returns number of actually allocated pages
1042  *
1043  * @total_in is used to return the number of bytes actually read.  It
1044  * may be smaller than the input length if we had to exit early because we
1045  * ran out of room in the pages array or because we cross the
1046  * max_out threshold.
1047  *
1048  * @total_out is an in/out parameter, must be set to the input length and will
1049  * be also used to return the total number of compressed bytes
1050  *
1051  * @max_out tells us the max number of bytes that we're allowed to
1052  * stuff into pages
1053  */
1054 int btrfs_compress_pages(unsigned int type_level, struct address_space *mapping,
1055                          u64 start, struct page **pages,
1056                          unsigned long *out_pages,
1057                          unsigned long *total_in,
1058                          unsigned long *total_out)
1059 {
1060         struct list_head *workspace;
1061         int ret;
1062         int type = type_level & 0xF;
1063 
1064         workspace = find_workspace(type);
1065 
1066         btrfs_compress_op[type - 1]->set_level(workspace, type_level);
1067         ret = btrfs_compress_op[type-1]->compress_pages(workspace, mapping,
1068                                                       start, pages,
1069                                                       out_pages,
1070                                                       total_in, total_out);
1071         free_workspace(type, workspace);
1072         return ret;
1073 }
1074 
1075 /*
1076  * pages_in is an array of pages with compressed data.
1077  *
1078  * disk_start is the starting logical offset of this array in the file
1079  *
1080  * orig_bio contains the pages from the file that we want to decompress into
1081  *
1082  * srclen is the number of bytes in pages_in
1083  *
1084  * The basic idea is that we have a bio that was created by readpages.
1085  * The pages in the bio are for the uncompressed data, and they may not
1086  * be contiguous.  They all correspond to the range of bytes covered by
1087  * the compressed extent.
1088  */
1089 static int btrfs_decompress_bio(struct compressed_bio *cb)
1090 {
1091         struct list_head *workspace;
1092         int ret;
1093         int type = cb->compress_type;
1094 
1095         workspace = find_workspace(type);
1096         ret = btrfs_compress_op[type - 1]->decompress_bio(workspace, cb);
1097         free_workspace(type, workspace);
1098 
1099         return ret;
1100 }
1101 
1102 /*
1103  * a less complex decompression routine.  Our compressed data fits in a
1104  * single page, and we want to read a single page out of it.
1105  * start_byte tells us the offset into the compressed data we're interested in
1106  */
1107 int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page,
1108                      unsigned long start_byte, size_t srclen, size_t destlen)
1109 {
1110         struct list_head *workspace;
1111         int ret;
1112 
1113         workspace = find_workspace(type);
1114 
1115         ret = btrfs_compress_op[type-1]->decompress(workspace, data_in,
1116                                                   dest_page, start_byte,
1117                                                   srclen, destlen);
1118 
1119         free_workspace(type, workspace);
1120         return ret;
1121 }
1122 
1123 void __cold btrfs_exit_compress(void)
1124 {
1125         free_workspaces();
1126 }
1127 
1128 /*
1129  * Copy uncompressed data from working buffer to pages.
1130  *
1131  * buf_start is the byte offset we're of the start of our workspace buffer.
1132  *
1133  * total_out is the last byte of the buffer
1134  */
1135 int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start,
1136                               unsigned long total_out, u64 disk_start,
1137                               struct bio *bio)
1138 {
1139         unsigned long buf_offset;
1140         unsigned long current_buf_start;
1141         unsigned long start_byte;
1142         unsigned long prev_start_byte;
1143         unsigned long working_bytes = total_out - buf_start;
1144         unsigned long bytes;
1145         char *kaddr;
1146         struct bio_vec bvec = bio_iter_iovec(bio, bio->bi_iter);
1147 
1148         /*
1149          * start byte is the first byte of the page we're currently
1150          * copying into relative to the start of the compressed data.
1151          */
1152         start_byte = page_offset(bvec.bv_page) - disk_start;
1153 
1154         /* we haven't yet hit data corresponding to this page */
1155         if (total_out <= start_byte)
1156                 return 1;
1157 
1158         /*
1159          * the start of the data we care about is offset into
1160          * the middle of our working buffer
1161          */
1162         if (total_out > start_byte && buf_start < start_byte) {
1163                 buf_offset = start_byte - buf_start;
1164                 working_bytes -= buf_offset;
1165         } else {
1166                 buf_offset = 0;
1167         }
1168         current_buf_start = buf_start;
1169 
1170         /* copy bytes from the working buffer into the pages */
1171         while (working_bytes > 0) {
1172                 bytes = min_t(unsigned long, bvec.bv_len,
1173                                 PAGE_SIZE - buf_offset);
1174                 bytes = min(bytes, working_bytes);
1175 
1176                 kaddr = kmap_atomic(bvec.bv_page);
1177                 memcpy(kaddr + bvec.bv_offset, buf + buf_offset, bytes);
1178                 kunmap_atomic(kaddr);
1179                 flush_dcache_page(bvec.bv_page);
1180 
1181                 buf_offset += bytes;
1182                 working_bytes -= bytes;
1183                 current_buf_start += bytes;
1184 
1185                 /* check if we need to pick another page */
1186                 bio_advance(bio, bytes);
1187                 if (!bio->bi_iter.bi_size)
1188                         return 0;
1189                 bvec = bio_iter_iovec(bio, bio->bi_iter);
1190                 prev_start_byte = start_byte;
1191                 start_byte = page_offset(bvec.bv_page) - disk_start;
1192 
1193                 /*
1194                  * We need to make sure we're only adjusting
1195                  * our offset into compression working buffer when
1196                  * we're switching pages.  Otherwise we can incorrectly
1197                  * keep copying when we were actually done.
1198                  */
1199                 if (start_byte != prev_start_byte) {
1200                         /*
1201                          * make sure our new page is covered by this
1202                          * working buffer
1203                          */
1204                         if (total_out <= start_byte)
1205                                 return 1;
1206 
1207                         /*
1208                          * the next page in the biovec might not be adjacent
1209                          * to the last page, but it might still be found
1210                          * inside this working buffer. bump our offset pointer
1211                          */
1212                         if (total_out > start_byte &&
1213                             current_buf_start < start_byte) {
1214                                 buf_offset = start_byte - buf_start;
1215                                 working_bytes = total_out - start_byte;
1216                                 current_buf_start = buf_start + buf_offset;
1217                         }
1218                 }
1219         }
1220 
1221         return 1;
1222 }
1223 
1224 /*
1225  * Shannon Entropy calculation
1226  *
1227  * Pure byte distribution analysis fails to determine compressiability of data.
1228  * Try calculating entropy to estimate the average minimum number of bits
1229  * needed to encode the sampled data.
1230  *
1231  * For convenience, return the percentage of needed bits, instead of amount of
1232  * bits directly.
1233  *
1234  * @ENTROPY_LVL_ACEPTABLE - below that threshold, sample has low byte entropy
1235  *                          and can be compressible with high probability
1236  *
1237  * @ENTROPY_LVL_HIGH - data are not compressible with high probability
1238  *
1239  * Use of ilog2() decreases precision, we lower the LVL to 5 to compensate.
1240  */
1241 #define ENTROPY_LVL_ACEPTABLE           (65)
1242 #define ENTROPY_LVL_HIGH                (80)
1243 
1244 /*
1245  * For increasead precision in shannon_entropy calculation,
1246  * let's do pow(n, M) to save more digits after comma:
1247  *
1248  * - maximum int bit length is 64
1249  * - ilog2(MAX_SAMPLE_SIZE)     -> 13
1250  * - 13 * 4 = 52 < 64           -> M = 4
1251  *
1252  * So use pow(n, 4).
1253  */
1254 static inline u32 ilog2_w(u64 n)
1255 {
1256         return ilog2(n * n * n * n);
1257 }
1258 
1259 static u32 shannon_entropy(struct heuristic_ws *ws)
1260 {
1261         const u32 entropy_max = 8 * ilog2_w(2);
1262         u32 entropy_sum = 0;
1263         u32 p, p_base, sz_base;
1264         u32 i;
1265 
1266         sz_base = ilog2_w(ws->sample_size);
1267         for (i = 0; i < BUCKET_SIZE && ws->bucket[i].count > 0; i++) {
1268                 p = ws->bucket[i].count;
1269                 p_base = ilog2_w(p);
1270                 entropy_sum += p * (sz_base - p_base);
1271         }
1272 
1273         entropy_sum /= ws->sample_size;
1274         return entropy_sum * 100 / entropy_max;
1275 }
1276 
1277 #define RADIX_BASE              4U
1278 #define COUNTERS_SIZE           (1U << RADIX_BASE)
1279 
1280 static u8 get4bits(u64 num, int shift) {
1281         u8 low4bits;
1282 
1283         num >>= shift;
1284         /* Reverse order */
1285         low4bits = (COUNTERS_SIZE - 1) - (num % COUNTERS_SIZE);
1286         return low4bits;
1287 }
1288 
1289 /*
1290  * Use 4 bits as radix base
1291  * Use 16 u32 counters for calculating new possition in buf array
1292  *
1293  * @array     - array that will be sorted
1294  * @array_buf - buffer array to store sorting results
1295  *              must be equal in size to @array
1296  * @num       - array size
1297  */
1298 static void radix_sort(struct bucket_item *array, struct bucket_item *array_buf,
1299                        int num)
1300 {
1301         u64 max_num;
1302         u64 buf_num;
1303         u32 counters[COUNTERS_SIZE];
1304         u32 new_addr;
1305         u32 addr;
1306         int bitlen;
1307         int shift;
1308         int i;
1309 
1310         /*
1311          * Try avoid useless loop iterations for small numbers stored in big
1312          * counters.  Example: 48 33 4 ... in 64bit array
1313          */
1314         max_num = array[0].count;
1315         for (i = 1; i < num; i++) {
1316                 buf_num = array[i].count;
1317                 if (buf_num > max_num)
1318                         max_num = buf_num;
1319         }
1320 
1321         buf_num = ilog2(max_num);
1322         bitlen = ALIGN(buf_num, RADIX_BASE * 2);
1323 
1324         shift = 0;
1325         while (shift < bitlen) {
1326                 memset(counters, 0, sizeof(counters));
1327 
1328                 for (i = 0; i < num; i++) {
1329                         buf_num = array[i].count;
1330                         addr = get4bits(buf_num, shift);
1331                         counters[addr]++;
1332                 }
1333 
1334                 for (i = 1; i < COUNTERS_SIZE; i++)
1335                         counters[i] += counters[i - 1];
1336 
1337                 for (i = num - 1; i >= 0; i--) {
1338                         buf_num = array[i].count;
1339                         addr = get4bits(buf_num, shift);
1340                         counters[addr]--;
1341                         new_addr = counters[addr];
1342                         array_buf[new_addr] = array[i];
1343                 }
1344 
1345                 shift += RADIX_BASE;
1346 
1347                 /*
1348                  * Normal radix expects to move data from a temporary array, to
1349                  * the main one.  But that requires some CPU time. Avoid that
1350                  * by doing another sort iteration to original array instead of
1351                  * memcpy()
1352                  */
1353                 memset(counters, 0, sizeof(counters));
1354 
1355                 for (i = 0; i < num; i ++) {
1356                         buf_num = array_buf[i].count;
1357                         addr = get4bits(buf_num, shift);
1358                         counters[addr]++;
1359                 }
1360 
1361                 for (i = 1; i < COUNTERS_SIZE; i++)
1362                         counters[i] += counters[i - 1];
1363 
1364                 for (i = num - 1; i >= 0; i--) {
1365                         buf_num = array_buf[i].count;
1366                         addr = get4bits(buf_num, shift);
1367                         counters[addr]--;
1368                         new_addr = counters[addr];
1369                         array[new_addr] = array_buf[i];
1370                 }
1371 
1372                 shift += RADIX_BASE;
1373         }
1374 }
1375 
1376 /*
1377  * Size of the core byte set - how many bytes cover 90% of the sample
1378  *
1379  * There are several types of structured binary data that use nearly all byte
1380  * values. The distribution can be uniform and counts in all buckets will be
1381  * nearly the same (eg. encrypted data). Unlikely to be compressible.
1382  *
1383  * Other possibility is normal (Gaussian) distribution, where the data could
1384  * be potentially compressible, but we have to take a few more steps to decide
1385  * how much.
1386  *
1387  * @BYTE_CORE_SET_LOW  - main part of byte values repeated frequently,
1388  *                       compression algo can easy fix that
1389  * @BYTE_CORE_SET_HIGH - data have uniform distribution and with high
1390  *                       probability is not compressible
1391  */
1392 #define BYTE_CORE_SET_LOW               (64)
1393 #define BYTE_CORE_SET_HIGH              (200)
1394 
1395 static int byte_core_set_size(struct heuristic_ws *ws)
1396 {
1397         u32 i;
1398         u32 coreset_sum = 0;
1399         const u32 core_set_threshold = ws->sample_size * 90 / 100;
1400         struct bucket_item *bucket = ws->bucket;
1401 
1402         /* Sort in reverse order */
1403         radix_sort(ws->bucket, ws->bucket_b, BUCKET_SIZE);
1404 
1405         for (i = 0; i < BYTE_CORE_SET_LOW; i++)
1406                 coreset_sum += bucket[i].count;
1407 
1408         if (coreset_sum > core_set_threshold)
1409                 return i;
1410 
1411         for (; i < BYTE_CORE_SET_HIGH && bucket[i].count > 0; i++) {
1412                 coreset_sum += bucket[i].count;
1413                 if (coreset_sum > core_set_threshold)
1414                         break;
1415         }
1416 
1417         return i;
1418 }
1419 
1420 /*
1421  * Count byte values in buckets.
1422  * This heuristic can detect textual data (configs, xml, json, html, etc).
1423  * Because in most text-like data byte set is restricted to limited number of
1424  * possible characters, and that restriction in most cases makes data easy to
1425  * compress.
1426  *
1427  * @BYTE_SET_THRESHOLD - consider all data within this byte set size:
1428  *      less - compressible
1429  *      more - need additional analysis
1430  */
1431 #define BYTE_SET_THRESHOLD              (64)
1432 
1433 static u32 byte_set_size(const struct heuristic_ws *ws)
1434 {
1435         u32 i;
1436         u32 byte_set_size = 0;
1437 
1438         for (i = 0; i < BYTE_SET_THRESHOLD; i++) {
1439                 if (ws->bucket[i].count > 0)
1440                         byte_set_size++;
1441         }
1442 
1443         /*
1444          * Continue collecting count of byte values in buckets.  If the byte
1445          * set size is bigger then the threshold, it's pointless to continue,
1446          * the detection technique would fail for this type of data.
1447          */
1448         for (; i < BUCKET_SIZE; i++) {
1449                 if (ws->bucket[i].count > 0) {
1450                         byte_set_size++;
1451                         if (byte_set_size > BYTE_SET_THRESHOLD)
1452                                 return byte_set_size;
1453                 }
1454         }
1455 
1456         return byte_set_size;
1457 }
1458 
1459 static bool sample_repeated_patterns(struct heuristic_ws *ws)
1460 {
1461         const u32 half_of_sample = ws->sample_size / 2;
1462         const u8 *data = ws->sample;
1463 
1464         return memcmp(&data[0], &data[half_of_sample], half_of_sample) == 0;
1465 }
1466 
1467 static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end,
1468                                      struct heuristic_ws *ws)
1469 {
1470         struct page *page;
1471         u64 index, index_end;
1472         u32 i, curr_sample_pos;
1473         u8 *in_data;
1474 
1475         /*
1476          * Compression handles the input data by chunks of 128KiB
1477          * (defined by BTRFS_MAX_UNCOMPRESSED)
1478          *
1479          * We do the same for the heuristic and loop over the whole range.
1480          *
1481          * MAX_SAMPLE_SIZE - calculated under assumption that heuristic will
1482          * process no more than BTRFS_MAX_UNCOMPRESSED at a time.
1483          */
1484         if (end - start > BTRFS_MAX_UNCOMPRESSED)
1485                 end = start + BTRFS_MAX_UNCOMPRESSED;
1486 
1487         index = start >> PAGE_SHIFT;
1488         index_end = end >> PAGE_SHIFT;
1489 
1490         /* Don't miss unaligned end */
1491         if (!IS_ALIGNED(end, PAGE_SIZE))
1492                 index_end++;
1493 
1494         curr_sample_pos = 0;
1495         while (index < index_end) {
1496                 page = find_get_page(inode->i_mapping, index);
1497                 in_data = kmap(page);
1498                 /* Handle case where the start is not aligned to PAGE_SIZE */
1499                 i = start % PAGE_SIZE;
1500                 while (i < PAGE_SIZE - SAMPLING_READ_SIZE) {
1501                         /* Don't sample any garbage from the last page */
1502                         if (start > end - SAMPLING_READ_SIZE)
1503                                 break;
1504                         memcpy(&ws->sample[curr_sample_pos], &in_data[i],
1505                                         SAMPLING_READ_SIZE);
1506                         i += SAMPLING_INTERVAL;
1507                         start += SAMPLING_INTERVAL;
1508                         curr_sample_pos += SAMPLING_READ_SIZE;
1509                 }
1510                 kunmap(page);
1511                 put_page(page);
1512 
1513                 index++;
1514         }
1515 
1516         ws->sample_size = curr_sample_pos;
1517 }
1518 
1519 /*
1520  * Compression heuristic.
1521  *
1522  * For now is's a naive and optimistic 'return true', we'll extend the logic to
1523  * quickly (compared to direct compression) detect data characteristics
1524  * (compressible/uncompressible) to avoid wasting CPU time on uncompressible
1525  * data.
1526  *
1527  * The following types of analysis can be performed:
1528  * - detect mostly zero data
1529  * - detect data with low "byte set" size (text, etc)
1530  * - detect data with low/high "core byte" set
1531  *
1532  * Return non-zero if the compression should be done, 0 otherwise.
1533  */
1534 int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
1535 {
1536         struct list_head *ws_list = __find_workspace(0, true);
1537         struct heuristic_ws *ws;
1538         u32 i;
1539         u8 byte;
1540         int ret = 0;
1541 
1542         ws = list_entry(ws_list, struct heuristic_ws, list);
1543 
1544         heuristic_collect_sample(inode, start, end, ws);
1545 
1546         if (sample_repeated_patterns(ws)) {
1547                 ret = 1;
1548                 goto out;
1549         }
1550 
1551         memset(ws->bucket, 0, sizeof(*ws->bucket)*BUCKET_SIZE);
1552 
1553         for (i = 0; i < ws->sample_size; i++) {
1554                 byte = ws->sample[i];
1555                 ws->bucket[byte].count++;
1556         }
1557 
1558         i = byte_set_size(ws);
1559         if (i < BYTE_SET_THRESHOLD) {
1560                 ret = 2;
1561                 goto out;
1562         }
1563 
1564         i = byte_core_set_size(ws);
1565         if (i <= BYTE_CORE_SET_LOW) {
1566                 ret = 3;
1567                 goto out;
1568         }
1569 
1570         if (i >= BYTE_CORE_SET_HIGH) {
1571                 ret = 0;
1572                 goto out;
1573         }
1574 
1575         i = shannon_entropy(ws);
1576         if (i <= ENTROPY_LVL_ACEPTABLE) {
1577                 ret = 4;
1578                 goto out;
1579         }
1580 
1581         /*
1582          * For the levels below ENTROPY_LVL_HIGH, additional analysis would be
1583          * needed to give green light to compression.
1584          *
1585          * For now just assume that compression at that level is not worth the
1586          * resources because:
1587          *
1588          * 1. it is possible to defrag the data later
1589          *
1590          * 2. the data would turn out to be hardly compressible, eg. 150 byte
1591          * values, every bucket has counter at level ~54. The heuristic would
1592          * be confused. This can happen when data have some internal repeated
1593          * patterns like "abbacbbc...". This can be detected by analyzing
1594          * pairs of bytes, which is too costly.
1595          */
1596         if (i < ENTROPY_LVL_HIGH) {
1597                 ret = 5;
1598                 goto out;
1599         } else {
1600                 ret = 0;
1601                 goto out;
1602         }
1603 
1604 out:
1605         __free_workspace(0, ws_list, true);
1606         return ret;
1607 }
1608 
1609 unsigned int btrfs_compress_str2level(const char *str)
1610 {
1611         if (strncmp(str, "zlib", 4) != 0)
1612                 return 0;
1613 
1614         /* Accepted form: zlib:1 up to zlib:9 and nothing left after the number */
1615         if (str[4] == ':' && '1' <= str[5] && str[5] <= '9' && str[6] == 0)
1616                 return str[5] - '';
1617 
1618         return BTRFS_ZLIB_DEFAULT_LEVEL;
1619 }
1620 

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