xref: /linux/fs/btrfs/compression.c (revision 3fd6c59042dbba50391e30862beac979491145fe)
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 <linux/shrinker.h>
24 #include <crypto/hash.h>
25 #include "misc.h"
26 #include "ctree.h"
27 #include "fs.h"
28 #include "btrfs_inode.h"
29 #include "bio.h"
30 #include "ordered-data.h"
31 #include "compression.h"
32 #include "extent_io.h"
33 #include "extent_map.h"
34 #include "subpage.h"
35 #include "messages.h"
36 #include "super.h"
37 
38 static struct bio_set btrfs_compressed_bioset;
39 
40 static const char* const btrfs_compress_types[] = { "", "zlib", "lzo", "zstd" };
41 
btrfs_compress_type2str(enum btrfs_compression_type type)42 const char* btrfs_compress_type2str(enum btrfs_compression_type type)
43 {
44 	switch (type) {
45 	case BTRFS_COMPRESS_ZLIB:
46 	case BTRFS_COMPRESS_LZO:
47 	case BTRFS_COMPRESS_ZSTD:
48 	case BTRFS_COMPRESS_NONE:
49 		return btrfs_compress_types[type];
50 	default:
51 		break;
52 	}
53 
54 	return NULL;
55 }
56 
to_compressed_bio(struct btrfs_bio * bbio)57 static inline struct compressed_bio *to_compressed_bio(struct btrfs_bio *bbio)
58 {
59 	return container_of(bbio, struct compressed_bio, bbio);
60 }
61 
alloc_compressed_bio(struct btrfs_inode * inode,u64 start,blk_opf_t op,btrfs_bio_end_io_t end_io)62 static struct compressed_bio *alloc_compressed_bio(struct btrfs_inode *inode,
63 						   u64 start, blk_opf_t op,
64 						   btrfs_bio_end_io_t end_io)
65 {
66 	struct btrfs_bio *bbio;
67 
68 	bbio = btrfs_bio(bio_alloc_bioset(NULL, BTRFS_MAX_COMPRESSED_PAGES, op,
69 					  GFP_NOFS, &btrfs_compressed_bioset));
70 	btrfs_bio_init(bbio, inode->root->fs_info, end_io, NULL);
71 	bbio->inode = inode;
72 	bbio->file_offset = start;
73 	return to_compressed_bio(bbio);
74 }
75 
btrfs_compress_is_valid_type(const char * str,size_t len)76 bool btrfs_compress_is_valid_type(const char *str, size_t len)
77 {
78 	int i;
79 
80 	for (i = 1; i < ARRAY_SIZE(btrfs_compress_types); i++) {
81 		size_t comp_len = strlen(btrfs_compress_types[i]);
82 
83 		if (len < comp_len)
84 			continue;
85 
86 		if (!strncmp(btrfs_compress_types[i], str, comp_len))
87 			return true;
88 	}
89 	return false;
90 }
91 
compression_compress_pages(int type,struct list_head * ws,struct address_space * mapping,u64 start,struct folio ** folios,unsigned long * out_folios,unsigned long * total_in,unsigned long * total_out)92 static int compression_compress_pages(int type, struct list_head *ws,
93 				      struct address_space *mapping, u64 start,
94 				      struct folio **folios, unsigned long *out_folios,
95 				      unsigned long *total_in, unsigned long *total_out)
96 {
97 	switch (type) {
98 	case BTRFS_COMPRESS_ZLIB:
99 		return zlib_compress_folios(ws, mapping, start, folios,
100 					    out_folios, total_in, total_out);
101 	case BTRFS_COMPRESS_LZO:
102 		return lzo_compress_folios(ws, mapping, start, folios,
103 					   out_folios, total_in, total_out);
104 	case BTRFS_COMPRESS_ZSTD:
105 		return zstd_compress_folios(ws, mapping, start, folios,
106 					    out_folios, total_in, total_out);
107 	case BTRFS_COMPRESS_NONE:
108 	default:
109 		/*
110 		 * This can happen when compression races with remount setting
111 		 * it to 'no compress', while caller doesn't call
112 		 * inode_need_compress() to check if we really need to
113 		 * compress.
114 		 *
115 		 * Not a big deal, just need to inform caller that we
116 		 * haven't allocated any pages yet.
117 		 */
118 		*out_folios = 0;
119 		return -E2BIG;
120 	}
121 }
122 
compression_decompress_bio(struct list_head * ws,struct compressed_bio * cb)123 static int compression_decompress_bio(struct list_head *ws,
124 				      struct compressed_bio *cb)
125 {
126 	switch (cb->compress_type) {
127 	case BTRFS_COMPRESS_ZLIB: return zlib_decompress_bio(ws, cb);
128 	case BTRFS_COMPRESS_LZO:  return lzo_decompress_bio(ws, cb);
129 	case BTRFS_COMPRESS_ZSTD: return zstd_decompress_bio(ws, cb);
130 	case BTRFS_COMPRESS_NONE:
131 	default:
132 		/*
133 		 * This can't happen, the type is validated several times
134 		 * before we get here.
135 		 */
136 		BUG();
137 	}
138 }
139 
compression_decompress(int type,struct list_head * ws,const u8 * data_in,struct folio * dest_folio,unsigned long dest_pgoff,size_t srclen,size_t destlen)140 static int compression_decompress(int type, struct list_head *ws,
141 		const u8 *data_in, struct folio *dest_folio,
142 		unsigned long dest_pgoff, size_t srclen, size_t destlen)
143 {
144 	switch (type) {
145 	case BTRFS_COMPRESS_ZLIB: return zlib_decompress(ws, data_in, dest_folio,
146 						dest_pgoff, srclen, destlen);
147 	case BTRFS_COMPRESS_LZO:  return lzo_decompress(ws, data_in, dest_folio,
148 						dest_pgoff, srclen, destlen);
149 	case BTRFS_COMPRESS_ZSTD: return zstd_decompress(ws, data_in, dest_folio,
150 						dest_pgoff, srclen, destlen);
151 	case BTRFS_COMPRESS_NONE:
152 	default:
153 		/*
154 		 * This can't happen, the type is validated several times
155 		 * before we get here.
156 		 */
157 		BUG();
158 	}
159 }
160 
btrfs_free_compressed_folios(struct compressed_bio * cb)161 static void btrfs_free_compressed_folios(struct compressed_bio *cb)
162 {
163 	for (unsigned int i = 0; i < cb->nr_folios; i++)
164 		btrfs_free_compr_folio(cb->compressed_folios[i]);
165 	kfree(cb->compressed_folios);
166 }
167 
168 static int btrfs_decompress_bio(struct compressed_bio *cb);
169 
170 /*
171  * Global cache of last unused pages for compression/decompression.
172  */
173 static struct btrfs_compr_pool {
174 	struct shrinker *shrinker;
175 	spinlock_t lock;
176 	struct list_head list;
177 	int count;
178 	int thresh;
179 } compr_pool;
180 
btrfs_compr_pool_count(struct shrinker * sh,struct shrink_control * sc)181 static unsigned long btrfs_compr_pool_count(struct shrinker *sh, struct shrink_control *sc)
182 {
183 	int ret;
184 
185 	/*
186 	 * We must not read the values more than once if 'ret' gets expanded in
187 	 * the return statement so we don't accidentally return a negative
188 	 * number, even if the first condition finds it positive.
189 	 */
190 	ret = READ_ONCE(compr_pool.count) - READ_ONCE(compr_pool.thresh);
191 
192 	return ret > 0 ? ret : 0;
193 }
194 
btrfs_compr_pool_scan(struct shrinker * sh,struct shrink_control * sc)195 static unsigned long btrfs_compr_pool_scan(struct shrinker *sh, struct shrink_control *sc)
196 {
197 	struct list_head remove;
198 	struct list_head *tmp, *next;
199 	int freed;
200 
201 	if (compr_pool.count == 0)
202 		return SHRINK_STOP;
203 
204 	INIT_LIST_HEAD(&remove);
205 
206 	/* For now, just simply drain the whole list. */
207 	spin_lock(&compr_pool.lock);
208 	list_splice_init(&compr_pool.list, &remove);
209 	freed = compr_pool.count;
210 	compr_pool.count = 0;
211 	spin_unlock(&compr_pool.lock);
212 
213 	list_for_each_safe(tmp, next, &remove) {
214 		struct page *page = list_entry(tmp, struct page, lru);
215 
216 		ASSERT(page_ref_count(page) == 1);
217 		put_page(page);
218 	}
219 
220 	return freed;
221 }
222 
223 /*
224  * Common wrappers for page allocation from compression wrappers
225  */
btrfs_alloc_compr_folio(void)226 struct folio *btrfs_alloc_compr_folio(void)
227 {
228 	struct folio *folio = NULL;
229 
230 	spin_lock(&compr_pool.lock);
231 	if (compr_pool.count > 0) {
232 		folio = list_first_entry(&compr_pool.list, struct folio, lru);
233 		list_del_init(&folio->lru);
234 		compr_pool.count--;
235 	}
236 	spin_unlock(&compr_pool.lock);
237 
238 	if (folio)
239 		return folio;
240 
241 	return folio_alloc(GFP_NOFS, 0);
242 }
243 
btrfs_free_compr_folio(struct folio * folio)244 void btrfs_free_compr_folio(struct folio *folio)
245 {
246 	bool do_free = false;
247 
248 	spin_lock(&compr_pool.lock);
249 	if (compr_pool.count > compr_pool.thresh) {
250 		do_free = true;
251 	} else {
252 		list_add(&folio->lru, &compr_pool.list);
253 		compr_pool.count++;
254 	}
255 	spin_unlock(&compr_pool.lock);
256 
257 	if (!do_free)
258 		return;
259 
260 	ASSERT(folio_ref_count(folio) == 1);
261 	folio_put(folio);
262 }
263 
end_bbio_compressed_read(struct btrfs_bio * bbio)264 static void end_bbio_compressed_read(struct btrfs_bio *bbio)
265 {
266 	struct compressed_bio *cb = to_compressed_bio(bbio);
267 	blk_status_t status = bbio->bio.bi_status;
268 
269 	if (!status)
270 		status = errno_to_blk_status(btrfs_decompress_bio(cb));
271 
272 	btrfs_free_compressed_folios(cb);
273 	btrfs_bio_end_io(cb->orig_bbio, status);
274 	bio_put(&bbio->bio);
275 }
276 
277 /*
278  * Clear the writeback bits on all of the file
279  * pages for a compressed write
280  */
end_compressed_writeback(const struct compressed_bio * cb)281 static noinline void end_compressed_writeback(const struct compressed_bio *cb)
282 {
283 	struct inode *inode = &cb->bbio.inode->vfs_inode;
284 	struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
285 	unsigned long index = cb->start >> PAGE_SHIFT;
286 	unsigned long end_index = (cb->start + cb->len - 1) >> PAGE_SHIFT;
287 	struct folio_batch fbatch;
288 	const int error = blk_status_to_errno(cb->bbio.bio.bi_status);
289 	int i;
290 	int ret;
291 
292 	if (error)
293 		mapping_set_error(inode->i_mapping, error);
294 
295 	folio_batch_init(&fbatch);
296 	while (index <= end_index) {
297 		ret = filemap_get_folios(inode->i_mapping, &index, end_index,
298 				&fbatch);
299 
300 		if (ret == 0)
301 			return;
302 
303 		for (i = 0; i < ret; i++) {
304 			struct folio *folio = fbatch.folios[i];
305 
306 			btrfs_folio_clamp_clear_writeback(fs_info, folio,
307 							  cb->start, cb->len);
308 		}
309 		folio_batch_release(&fbatch);
310 	}
311 	/* the inode may be gone now */
312 }
313 
btrfs_finish_compressed_write_work(struct work_struct * work)314 static void btrfs_finish_compressed_write_work(struct work_struct *work)
315 {
316 	struct compressed_bio *cb =
317 		container_of(work, struct compressed_bio, write_end_work);
318 
319 	btrfs_finish_ordered_extent(cb->bbio.ordered, NULL, cb->start, cb->len,
320 				    cb->bbio.bio.bi_status == BLK_STS_OK);
321 
322 	if (cb->writeback)
323 		end_compressed_writeback(cb);
324 	/* Note, our inode could be gone now */
325 
326 	btrfs_free_compressed_folios(cb);
327 	bio_put(&cb->bbio.bio);
328 }
329 
330 /*
331  * Do the cleanup once all the compressed pages hit the disk.  This will clear
332  * writeback on the file pages and free the compressed pages.
333  *
334  * This also calls the writeback end hooks for the file pages so that metadata
335  * and checksums can be updated in the file.
336  */
end_bbio_compressed_write(struct btrfs_bio * bbio)337 static void end_bbio_compressed_write(struct btrfs_bio *bbio)
338 {
339 	struct compressed_bio *cb = to_compressed_bio(bbio);
340 	struct btrfs_fs_info *fs_info = bbio->inode->root->fs_info;
341 
342 	queue_work(fs_info->compressed_write_workers, &cb->write_end_work);
343 }
344 
btrfs_add_compressed_bio_folios(struct compressed_bio * cb)345 static void btrfs_add_compressed_bio_folios(struct compressed_bio *cb)
346 {
347 	struct bio *bio = &cb->bbio.bio;
348 	u32 offset = 0;
349 
350 	while (offset < cb->compressed_len) {
351 		int ret;
352 		u32 len = min_t(u32, cb->compressed_len - offset, PAGE_SIZE);
353 
354 		/* Maximum compressed extent is smaller than bio size limit. */
355 		ret = bio_add_folio(bio, cb->compressed_folios[offset >> PAGE_SHIFT],
356 				    len, 0);
357 		ASSERT(ret);
358 		offset += len;
359 	}
360 }
361 
362 /*
363  * worker function to build and submit bios for previously compressed pages.
364  * The corresponding pages in the inode should be marked for writeback
365  * and the compressed pages should have a reference on them for dropping
366  * when the IO is complete.
367  *
368  * This also checksums the file bytes and gets things ready for
369  * the end io hooks.
370  */
btrfs_submit_compressed_write(struct btrfs_ordered_extent * ordered,struct folio ** compressed_folios,unsigned int nr_folios,blk_opf_t write_flags,bool writeback)371 void btrfs_submit_compressed_write(struct btrfs_ordered_extent *ordered,
372 				   struct folio **compressed_folios,
373 				   unsigned int nr_folios,
374 				   blk_opf_t write_flags,
375 				   bool writeback)
376 {
377 	struct btrfs_inode *inode = ordered->inode;
378 	struct btrfs_fs_info *fs_info = inode->root->fs_info;
379 	struct compressed_bio *cb;
380 
381 	ASSERT(IS_ALIGNED(ordered->file_offset, fs_info->sectorsize));
382 	ASSERT(IS_ALIGNED(ordered->num_bytes, fs_info->sectorsize));
383 
384 	cb = alloc_compressed_bio(inode, ordered->file_offset,
385 				  REQ_OP_WRITE | write_flags,
386 				  end_bbio_compressed_write);
387 	cb->start = ordered->file_offset;
388 	cb->len = ordered->num_bytes;
389 	cb->compressed_folios = compressed_folios;
390 	cb->compressed_len = ordered->disk_num_bytes;
391 	cb->writeback = writeback;
392 	INIT_WORK(&cb->write_end_work, btrfs_finish_compressed_write_work);
393 	cb->nr_folios = nr_folios;
394 	cb->bbio.bio.bi_iter.bi_sector = ordered->disk_bytenr >> SECTOR_SHIFT;
395 	cb->bbio.ordered = ordered;
396 	btrfs_add_compressed_bio_folios(cb);
397 
398 	btrfs_submit_bbio(&cb->bbio, 0);
399 }
400 
401 /*
402  * Add extra pages in the same compressed file extent so that we don't need to
403  * re-read the same extent again and again.
404  *
405  * NOTE: this won't work well for subpage, as for subpage read, we lock the
406  * full page then submit bio for each compressed/regular extents.
407  *
408  * This means, if we have several sectors in the same page points to the same
409  * on-disk compressed data, we will re-read the same extent many times and
410  * this function can only help for the next page.
411  */
add_ra_bio_pages(struct inode * inode,u64 compressed_end,struct compressed_bio * cb,int * memstall,unsigned long * pflags)412 static noinline int add_ra_bio_pages(struct inode *inode,
413 				     u64 compressed_end,
414 				     struct compressed_bio *cb,
415 				     int *memstall, unsigned long *pflags)
416 {
417 	struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
418 	unsigned long end_index;
419 	struct bio *orig_bio = &cb->orig_bbio->bio;
420 	u64 cur = cb->orig_bbio->file_offset + orig_bio->bi_iter.bi_size;
421 	u64 isize = i_size_read(inode);
422 	int ret;
423 	struct folio *folio;
424 	struct extent_map *em;
425 	struct address_space *mapping = inode->i_mapping;
426 	struct extent_map_tree *em_tree;
427 	struct extent_io_tree *tree;
428 	int sectors_missed = 0;
429 
430 	em_tree = &BTRFS_I(inode)->extent_tree;
431 	tree = &BTRFS_I(inode)->io_tree;
432 
433 	if (isize == 0)
434 		return 0;
435 
436 	/*
437 	 * For current subpage support, we only support 64K page size,
438 	 * which means maximum compressed extent size (128K) is just 2x page
439 	 * size.
440 	 * This makes readahead less effective, so here disable readahead for
441 	 * subpage for now, until full compressed write is supported.
442 	 */
443 	if (fs_info->sectorsize < PAGE_SIZE)
444 		return 0;
445 
446 	end_index = (i_size_read(inode) - 1) >> PAGE_SHIFT;
447 
448 	while (cur < compressed_end) {
449 		u64 page_end;
450 		u64 pg_index = cur >> PAGE_SHIFT;
451 		u32 add_size;
452 
453 		if (pg_index > end_index)
454 			break;
455 
456 		folio = filemap_get_folio(mapping, pg_index);
457 		if (!IS_ERR(folio)) {
458 			u64 folio_sz = folio_size(folio);
459 			u64 offset = offset_in_folio(folio, cur);
460 
461 			folio_put(folio);
462 			sectors_missed += (folio_sz - offset) >>
463 					  fs_info->sectorsize_bits;
464 
465 			/* Beyond threshold, no need to continue */
466 			if (sectors_missed > 4)
467 				break;
468 
469 			/*
470 			 * Jump to next page start as we already have page for
471 			 * current offset.
472 			 */
473 			cur += (folio_sz - offset);
474 			continue;
475 		}
476 
477 		folio = filemap_alloc_folio(mapping_gfp_constraint(mapping,
478 								   ~__GFP_FS), 0);
479 		if (!folio)
480 			break;
481 
482 		if (filemap_add_folio(mapping, folio, pg_index, GFP_NOFS)) {
483 			/* There is already a page, skip to page end */
484 			cur += folio_size(folio);
485 			folio_put(folio);
486 			continue;
487 		}
488 
489 		if (!*memstall && folio_test_workingset(folio)) {
490 			psi_memstall_enter(pflags);
491 			*memstall = 1;
492 		}
493 
494 		ret = set_folio_extent_mapped(folio);
495 		if (ret < 0) {
496 			folio_unlock(folio);
497 			folio_put(folio);
498 			break;
499 		}
500 
501 		page_end = (pg_index << PAGE_SHIFT) + folio_size(folio) - 1;
502 		lock_extent(tree, cur, page_end, NULL);
503 		read_lock(&em_tree->lock);
504 		em = lookup_extent_mapping(em_tree, cur, page_end + 1 - cur);
505 		read_unlock(&em_tree->lock);
506 
507 		/*
508 		 * At this point, we have a locked page in the page cache for
509 		 * these bytes in the file.  But, we have to make sure they map
510 		 * to this compressed extent on disk.
511 		 */
512 		if (!em || cur < em->start ||
513 		    (cur + fs_info->sectorsize > extent_map_end(em)) ||
514 		    (extent_map_block_start(em) >> SECTOR_SHIFT) !=
515 		    orig_bio->bi_iter.bi_sector) {
516 			free_extent_map(em);
517 			unlock_extent(tree, cur, page_end, NULL);
518 			folio_unlock(folio);
519 			folio_put(folio);
520 			break;
521 		}
522 		add_size = min(em->start + em->len, page_end + 1) - cur;
523 		free_extent_map(em);
524 		unlock_extent(tree, cur, page_end, NULL);
525 
526 		if (folio->index == end_index) {
527 			size_t zero_offset = offset_in_folio(folio, isize);
528 
529 			if (zero_offset) {
530 				int zeros;
531 				zeros = folio_size(folio) - zero_offset;
532 				folio_zero_range(folio, zero_offset, zeros);
533 			}
534 		}
535 
536 		if (!bio_add_folio(orig_bio, folio, add_size,
537 				   offset_in_folio(folio, cur))) {
538 			folio_unlock(folio);
539 			folio_put(folio);
540 			break;
541 		}
542 		/*
543 		 * If it's subpage, we also need to increase its
544 		 * subpage::readers number, as at endio we will decrease
545 		 * subpage::readers and to unlock the page.
546 		 */
547 		if (fs_info->sectorsize < PAGE_SIZE)
548 			btrfs_folio_set_lock(fs_info, folio, cur, add_size);
549 		folio_put(folio);
550 		cur += add_size;
551 	}
552 	return 0;
553 }
554 
555 /*
556  * for a compressed read, the bio we get passed has all the inode pages
557  * in it.  We don't actually do IO on those pages but allocate new ones
558  * to hold the compressed pages on disk.
559  *
560  * bio->bi_iter.bi_sector points to the compressed extent on disk
561  * bio->bi_io_vec points to all of the inode pages
562  *
563  * After the compressed pages are read, we copy the bytes into the
564  * bio we were passed and then call the bio end_io calls
565  */
btrfs_submit_compressed_read(struct btrfs_bio * bbio)566 void btrfs_submit_compressed_read(struct btrfs_bio *bbio)
567 {
568 	struct btrfs_inode *inode = bbio->inode;
569 	struct btrfs_fs_info *fs_info = inode->root->fs_info;
570 	struct extent_map_tree *em_tree = &inode->extent_tree;
571 	struct compressed_bio *cb;
572 	unsigned int compressed_len;
573 	u64 file_offset = bbio->file_offset;
574 	u64 em_len;
575 	u64 em_start;
576 	struct extent_map *em;
577 	unsigned long pflags;
578 	int memstall = 0;
579 	blk_status_t ret;
580 	int ret2;
581 
582 	/* we need the actual starting offset of this extent in the file */
583 	read_lock(&em_tree->lock);
584 	em = lookup_extent_mapping(em_tree, file_offset, fs_info->sectorsize);
585 	read_unlock(&em_tree->lock);
586 	if (!em) {
587 		ret = BLK_STS_IOERR;
588 		goto out;
589 	}
590 
591 	ASSERT(extent_map_is_compressed(em));
592 	compressed_len = em->disk_num_bytes;
593 
594 	cb = alloc_compressed_bio(inode, file_offset, REQ_OP_READ,
595 				  end_bbio_compressed_read);
596 
597 	cb->start = em->start - em->offset;
598 	em_len = em->len;
599 	em_start = em->start;
600 
601 	cb->len = bbio->bio.bi_iter.bi_size;
602 	cb->compressed_len = compressed_len;
603 	cb->compress_type = extent_map_compression(em);
604 	cb->orig_bbio = bbio;
605 
606 	free_extent_map(em);
607 
608 	cb->nr_folios = DIV_ROUND_UP(compressed_len, PAGE_SIZE);
609 	cb->compressed_folios = kcalloc(cb->nr_folios, sizeof(struct page *), GFP_NOFS);
610 	if (!cb->compressed_folios) {
611 		ret = BLK_STS_RESOURCE;
612 		goto out_free_bio;
613 	}
614 
615 	ret2 = btrfs_alloc_folio_array(cb->nr_folios, cb->compressed_folios);
616 	if (ret2) {
617 		ret = BLK_STS_RESOURCE;
618 		goto out_free_compressed_pages;
619 	}
620 
621 	add_ra_bio_pages(&inode->vfs_inode, em_start + em_len, cb, &memstall,
622 			 &pflags);
623 
624 	/* include any pages we added in add_ra-bio_pages */
625 	cb->len = bbio->bio.bi_iter.bi_size;
626 	cb->bbio.bio.bi_iter.bi_sector = bbio->bio.bi_iter.bi_sector;
627 	btrfs_add_compressed_bio_folios(cb);
628 
629 	if (memstall)
630 		psi_memstall_leave(&pflags);
631 
632 	btrfs_submit_bbio(&cb->bbio, 0);
633 	return;
634 
635 out_free_compressed_pages:
636 	kfree(cb->compressed_folios);
637 out_free_bio:
638 	bio_put(&cb->bbio.bio);
639 out:
640 	btrfs_bio_end_io(bbio, ret);
641 }
642 
643 /*
644  * Heuristic uses systematic sampling to collect data from the input data
645  * range, the logic can be tuned by the following constants:
646  *
647  * @SAMPLING_READ_SIZE - how many bytes will be copied from for each sample
648  * @SAMPLING_INTERVAL  - range from which the sampled data can be collected
649  */
650 #define SAMPLING_READ_SIZE	(16)
651 #define SAMPLING_INTERVAL	(256)
652 
653 /*
654  * For statistical analysis of the input data we consider bytes that form a
655  * Galois Field of 256 objects. Each object has an attribute count, ie. how
656  * many times the object appeared in the sample.
657  */
658 #define BUCKET_SIZE		(256)
659 
660 /*
661  * The size of the sample is based on a statistical sampling rule of thumb.
662  * The common way is to perform sampling tests as long as the number of
663  * elements in each cell is at least 5.
664  *
665  * Instead of 5, we choose 32 to obtain more accurate results.
666  * If the data contain the maximum number of symbols, which is 256, we obtain a
667  * sample size bound by 8192.
668  *
669  * For a sample of at most 8KB of data per data range: 16 consecutive bytes
670  * from up to 512 locations.
671  */
672 #define MAX_SAMPLE_SIZE		(BTRFS_MAX_UNCOMPRESSED *		\
673 				 SAMPLING_READ_SIZE / SAMPLING_INTERVAL)
674 
675 struct bucket_item {
676 	u32 count;
677 };
678 
679 struct heuristic_ws {
680 	/* Partial copy of input data */
681 	u8 *sample;
682 	u32 sample_size;
683 	/* Buckets store counters for each byte value */
684 	struct bucket_item *bucket;
685 	/* Sorting buffer */
686 	struct bucket_item *bucket_b;
687 	struct list_head list;
688 };
689 
690 static struct workspace_manager heuristic_wsm;
691 
free_heuristic_ws(struct list_head * ws)692 static void free_heuristic_ws(struct list_head *ws)
693 {
694 	struct heuristic_ws *workspace;
695 
696 	workspace = list_entry(ws, struct heuristic_ws, list);
697 
698 	kvfree(workspace->sample);
699 	kfree(workspace->bucket);
700 	kfree(workspace->bucket_b);
701 	kfree(workspace);
702 }
703 
alloc_heuristic_ws(void)704 static struct list_head *alloc_heuristic_ws(void)
705 {
706 	struct heuristic_ws *ws;
707 
708 	ws = kzalloc(sizeof(*ws), GFP_KERNEL);
709 	if (!ws)
710 		return ERR_PTR(-ENOMEM);
711 
712 	ws->sample = kvmalloc(MAX_SAMPLE_SIZE, GFP_KERNEL);
713 	if (!ws->sample)
714 		goto fail;
715 
716 	ws->bucket = kcalloc(BUCKET_SIZE, sizeof(*ws->bucket), GFP_KERNEL);
717 	if (!ws->bucket)
718 		goto fail;
719 
720 	ws->bucket_b = kcalloc(BUCKET_SIZE, sizeof(*ws->bucket_b), GFP_KERNEL);
721 	if (!ws->bucket_b)
722 		goto fail;
723 
724 	INIT_LIST_HEAD(&ws->list);
725 	return &ws->list;
726 fail:
727 	free_heuristic_ws(&ws->list);
728 	return ERR_PTR(-ENOMEM);
729 }
730 
731 const struct btrfs_compress_op btrfs_heuristic_compress = {
732 	.workspace_manager = &heuristic_wsm,
733 };
734 
735 static const struct btrfs_compress_op * const btrfs_compress_op[] = {
736 	/* The heuristic is represented as compression type 0 */
737 	&btrfs_heuristic_compress,
738 	&btrfs_zlib_compress,
739 	&btrfs_lzo_compress,
740 	&btrfs_zstd_compress,
741 };
742 
alloc_workspace(int type,unsigned int level)743 static struct list_head *alloc_workspace(int type, unsigned int level)
744 {
745 	switch (type) {
746 	case BTRFS_COMPRESS_NONE: return alloc_heuristic_ws();
747 	case BTRFS_COMPRESS_ZLIB: return zlib_alloc_workspace(level);
748 	case BTRFS_COMPRESS_LZO:  return lzo_alloc_workspace();
749 	case BTRFS_COMPRESS_ZSTD: return zstd_alloc_workspace(level);
750 	default:
751 		/*
752 		 * This can't happen, the type is validated several times
753 		 * before we get here.
754 		 */
755 		BUG();
756 	}
757 }
758 
free_workspace(int type,struct list_head * ws)759 static void free_workspace(int type, struct list_head *ws)
760 {
761 	switch (type) {
762 	case BTRFS_COMPRESS_NONE: return free_heuristic_ws(ws);
763 	case BTRFS_COMPRESS_ZLIB: return zlib_free_workspace(ws);
764 	case BTRFS_COMPRESS_LZO:  return lzo_free_workspace(ws);
765 	case BTRFS_COMPRESS_ZSTD: return zstd_free_workspace(ws);
766 	default:
767 		/*
768 		 * This can't happen, the type is validated several times
769 		 * before we get here.
770 		 */
771 		BUG();
772 	}
773 }
774 
btrfs_init_workspace_manager(int type)775 static void btrfs_init_workspace_manager(int type)
776 {
777 	struct workspace_manager *wsm;
778 	struct list_head *workspace;
779 
780 	wsm = btrfs_compress_op[type]->workspace_manager;
781 	INIT_LIST_HEAD(&wsm->idle_ws);
782 	spin_lock_init(&wsm->ws_lock);
783 	atomic_set(&wsm->total_ws, 0);
784 	init_waitqueue_head(&wsm->ws_wait);
785 
786 	/*
787 	 * Preallocate one workspace for each compression type so we can
788 	 * guarantee forward progress in the worst case
789 	 */
790 	workspace = alloc_workspace(type, 0);
791 	if (IS_ERR(workspace)) {
792 		pr_warn(
793 	"BTRFS: cannot preallocate compression workspace, will try later\n");
794 	} else {
795 		atomic_set(&wsm->total_ws, 1);
796 		wsm->free_ws = 1;
797 		list_add(workspace, &wsm->idle_ws);
798 	}
799 }
800 
btrfs_cleanup_workspace_manager(int type)801 static void btrfs_cleanup_workspace_manager(int type)
802 {
803 	struct workspace_manager *wsman;
804 	struct list_head *ws;
805 
806 	wsman = btrfs_compress_op[type]->workspace_manager;
807 	while (!list_empty(&wsman->idle_ws)) {
808 		ws = wsman->idle_ws.next;
809 		list_del(ws);
810 		free_workspace(type, ws);
811 		atomic_dec(&wsman->total_ws);
812 	}
813 }
814 
815 /*
816  * This finds an available workspace or allocates a new one.
817  * If it's not possible to allocate a new one, waits until there's one.
818  * Preallocation makes a forward progress guarantees and we do not return
819  * errors.
820  */
btrfs_get_workspace(int type,unsigned int level)821 struct list_head *btrfs_get_workspace(int type, unsigned int level)
822 {
823 	struct workspace_manager *wsm;
824 	struct list_head *workspace;
825 	int cpus = num_online_cpus();
826 	unsigned nofs_flag;
827 	struct list_head *idle_ws;
828 	spinlock_t *ws_lock;
829 	atomic_t *total_ws;
830 	wait_queue_head_t *ws_wait;
831 	int *free_ws;
832 
833 	wsm = btrfs_compress_op[type]->workspace_manager;
834 	idle_ws	 = &wsm->idle_ws;
835 	ws_lock	 = &wsm->ws_lock;
836 	total_ws = &wsm->total_ws;
837 	ws_wait	 = &wsm->ws_wait;
838 	free_ws	 = &wsm->free_ws;
839 
840 again:
841 	spin_lock(ws_lock);
842 	if (!list_empty(idle_ws)) {
843 		workspace = idle_ws->next;
844 		list_del(workspace);
845 		(*free_ws)--;
846 		spin_unlock(ws_lock);
847 		return workspace;
848 
849 	}
850 	if (atomic_read(total_ws) > cpus) {
851 		DEFINE_WAIT(wait);
852 
853 		spin_unlock(ws_lock);
854 		prepare_to_wait(ws_wait, &wait, TASK_UNINTERRUPTIBLE);
855 		if (atomic_read(total_ws) > cpus && !*free_ws)
856 			schedule();
857 		finish_wait(ws_wait, &wait);
858 		goto again;
859 	}
860 	atomic_inc(total_ws);
861 	spin_unlock(ws_lock);
862 
863 	/*
864 	 * Allocation helpers call vmalloc that can't use GFP_NOFS, so we have
865 	 * to turn it off here because we might get called from the restricted
866 	 * context of btrfs_compress_bio/btrfs_compress_pages
867 	 */
868 	nofs_flag = memalloc_nofs_save();
869 	workspace = alloc_workspace(type, level);
870 	memalloc_nofs_restore(nofs_flag);
871 
872 	if (IS_ERR(workspace)) {
873 		atomic_dec(total_ws);
874 		wake_up(ws_wait);
875 
876 		/*
877 		 * Do not return the error but go back to waiting. There's a
878 		 * workspace preallocated for each type and the compression
879 		 * time is bounded so we get to a workspace eventually. This
880 		 * makes our caller's life easier.
881 		 *
882 		 * To prevent silent and low-probability deadlocks (when the
883 		 * initial preallocation fails), check if there are any
884 		 * workspaces at all.
885 		 */
886 		if (atomic_read(total_ws) == 0) {
887 			static DEFINE_RATELIMIT_STATE(_rs,
888 					/* once per minute */ 60 * HZ,
889 					/* no burst */ 1);
890 
891 			if (__ratelimit(&_rs)) {
892 				pr_warn("BTRFS: no compression workspaces, low memory, retrying\n");
893 			}
894 		}
895 		goto again;
896 	}
897 	return workspace;
898 }
899 
get_workspace(int type,int level)900 static struct list_head *get_workspace(int type, int level)
901 {
902 	switch (type) {
903 	case BTRFS_COMPRESS_NONE: return btrfs_get_workspace(type, level);
904 	case BTRFS_COMPRESS_ZLIB: return zlib_get_workspace(level);
905 	case BTRFS_COMPRESS_LZO:  return btrfs_get_workspace(type, level);
906 	case BTRFS_COMPRESS_ZSTD: return zstd_get_workspace(level);
907 	default:
908 		/*
909 		 * This can't happen, the type is validated several times
910 		 * before we get here.
911 		 */
912 		BUG();
913 	}
914 }
915 
916 /*
917  * put a workspace struct back on the list or free it if we have enough
918  * idle ones sitting around
919  */
btrfs_put_workspace(int type,struct list_head * ws)920 void btrfs_put_workspace(int type, struct list_head *ws)
921 {
922 	struct workspace_manager *wsm;
923 	struct list_head *idle_ws;
924 	spinlock_t *ws_lock;
925 	atomic_t *total_ws;
926 	wait_queue_head_t *ws_wait;
927 	int *free_ws;
928 
929 	wsm = btrfs_compress_op[type]->workspace_manager;
930 	idle_ws	 = &wsm->idle_ws;
931 	ws_lock	 = &wsm->ws_lock;
932 	total_ws = &wsm->total_ws;
933 	ws_wait	 = &wsm->ws_wait;
934 	free_ws	 = &wsm->free_ws;
935 
936 	spin_lock(ws_lock);
937 	if (*free_ws <= num_online_cpus()) {
938 		list_add(ws, idle_ws);
939 		(*free_ws)++;
940 		spin_unlock(ws_lock);
941 		goto wake;
942 	}
943 	spin_unlock(ws_lock);
944 
945 	free_workspace(type, ws);
946 	atomic_dec(total_ws);
947 wake:
948 	cond_wake_up(ws_wait);
949 }
950 
put_workspace(int type,struct list_head * ws)951 static void put_workspace(int type, struct list_head *ws)
952 {
953 	switch (type) {
954 	case BTRFS_COMPRESS_NONE: return btrfs_put_workspace(type, ws);
955 	case BTRFS_COMPRESS_ZLIB: return btrfs_put_workspace(type, ws);
956 	case BTRFS_COMPRESS_LZO:  return btrfs_put_workspace(type, ws);
957 	case BTRFS_COMPRESS_ZSTD: return zstd_put_workspace(ws);
958 	default:
959 		/*
960 		 * This can't happen, the type is validated several times
961 		 * before we get here.
962 		 */
963 		BUG();
964 	}
965 }
966 
967 /*
968  * Adjust @level according to the limits of the compression algorithm or
969  * fallback to default
970  */
btrfs_compress_set_level(int type,unsigned level)971 static unsigned int btrfs_compress_set_level(int type, unsigned level)
972 {
973 	const struct btrfs_compress_op *ops = btrfs_compress_op[type];
974 
975 	if (level == 0)
976 		level = ops->default_level;
977 	else
978 		level = min(level, ops->max_level);
979 
980 	return level;
981 }
982 
983 /* Wrapper around find_get_page(), with extra error message. */
btrfs_compress_filemap_get_folio(struct address_space * mapping,u64 start,struct folio ** in_folio_ret)984 int btrfs_compress_filemap_get_folio(struct address_space *mapping, u64 start,
985 				     struct folio **in_folio_ret)
986 {
987 	struct folio *in_folio;
988 
989 	/*
990 	 * The compressed write path should have the folio locked already, thus
991 	 * we only need to grab one reference.
992 	 */
993 	in_folio = filemap_get_folio(mapping, start >> PAGE_SHIFT);
994 	if (IS_ERR(in_folio)) {
995 		struct btrfs_inode *inode = BTRFS_I(mapping->host);
996 
997 		btrfs_crit(inode->root->fs_info,
998 		"failed to get page cache, root %lld ino %llu file offset %llu",
999 			   btrfs_root_id(inode->root), btrfs_ino(inode), start);
1000 		return -ENOENT;
1001 	}
1002 	*in_folio_ret = in_folio;
1003 	return 0;
1004 }
1005 
1006 /*
1007  * Given an address space and start and length, compress the bytes into @pages
1008  * that are allocated on demand.
1009  *
1010  * @type_level is encoded algorithm and level, where level 0 means whatever
1011  * default the algorithm chooses and is opaque here;
1012  * - compression algo are 0-3
1013  * - the level are bits 4-7
1014  *
1015  * @out_pages is an in/out parameter, holds maximum number of pages to allocate
1016  * and returns number of actually allocated pages
1017  *
1018  * @total_in is used to return the number of bytes actually read.  It
1019  * may be smaller than the input length if we had to exit early because we
1020  * ran out of room in the pages array or because we cross the
1021  * max_out threshold.
1022  *
1023  * @total_out is an in/out parameter, must be set to the input length and will
1024  * be also used to return the total number of compressed bytes
1025  */
btrfs_compress_folios(unsigned int type_level,struct address_space * mapping,u64 start,struct folio ** folios,unsigned long * out_folios,unsigned long * total_in,unsigned long * total_out)1026 int btrfs_compress_folios(unsigned int type_level, struct address_space *mapping,
1027 			 u64 start, struct folio **folios, unsigned long *out_folios,
1028 			 unsigned long *total_in, unsigned long *total_out)
1029 {
1030 	int type = btrfs_compress_type(type_level);
1031 	int level = btrfs_compress_level(type_level);
1032 	const unsigned long orig_len = *total_out;
1033 	struct list_head *workspace;
1034 	int ret;
1035 
1036 	level = btrfs_compress_set_level(type, level);
1037 	workspace = get_workspace(type, level);
1038 	ret = compression_compress_pages(type, workspace, mapping, start, folios,
1039 					 out_folios, total_in, total_out);
1040 	/* The total read-in bytes should be no larger than the input. */
1041 	ASSERT(*total_in <= orig_len);
1042 	put_workspace(type, workspace);
1043 	return ret;
1044 }
1045 
btrfs_decompress_bio(struct compressed_bio * cb)1046 static int btrfs_decompress_bio(struct compressed_bio *cb)
1047 {
1048 	struct list_head *workspace;
1049 	int ret;
1050 	int type = cb->compress_type;
1051 
1052 	workspace = get_workspace(type, 0);
1053 	ret = compression_decompress_bio(workspace, cb);
1054 	put_workspace(type, workspace);
1055 
1056 	if (!ret)
1057 		zero_fill_bio(&cb->orig_bbio->bio);
1058 	return ret;
1059 }
1060 
1061 /*
1062  * a less complex decompression routine.  Our compressed data fits in a
1063  * single page, and we want to read a single page out of it.
1064  * start_byte tells us the offset into the compressed data we're interested in
1065  */
btrfs_decompress(int type,const u8 * data_in,struct folio * dest_folio,unsigned long dest_pgoff,size_t srclen,size_t destlen)1066 int btrfs_decompress(int type, const u8 *data_in, struct folio *dest_folio,
1067 		     unsigned long dest_pgoff, size_t srclen, size_t destlen)
1068 {
1069 	struct btrfs_fs_info *fs_info = folio_to_fs_info(dest_folio);
1070 	struct list_head *workspace;
1071 	const u32 sectorsize = fs_info->sectorsize;
1072 	int ret;
1073 
1074 	/*
1075 	 * The full destination page range should not exceed the page size.
1076 	 * And the @destlen should not exceed sectorsize, as this is only called for
1077 	 * inline file extents, which should not exceed sectorsize.
1078 	 */
1079 	ASSERT(dest_pgoff + destlen <= PAGE_SIZE && destlen <= sectorsize);
1080 
1081 	workspace = get_workspace(type, 0);
1082 	ret = compression_decompress(type, workspace, data_in, dest_folio,
1083 				     dest_pgoff, srclen, destlen);
1084 	put_workspace(type, workspace);
1085 
1086 	return ret;
1087 }
1088 
btrfs_init_compress(void)1089 int __init btrfs_init_compress(void)
1090 {
1091 	if (bioset_init(&btrfs_compressed_bioset, BIO_POOL_SIZE,
1092 			offsetof(struct compressed_bio, bbio.bio),
1093 			BIOSET_NEED_BVECS))
1094 		return -ENOMEM;
1095 
1096 	compr_pool.shrinker = shrinker_alloc(SHRINKER_NONSLAB, "btrfs-compr-pages");
1097 	if (!compr_pool.shrinker)
1098 		return -ENOMEM;
1099 
1100 	btrfs_init_workspace_manager(BTRFS_COMPRESS_NONE);
1101 	btrfs_init_workspace_manager(BTRFS_COMPRESS_ZLIB);
1102 	btrfs_init_workspace_manager(BTRFS_COMPRESS_LZO);
1103 	zstd_init_workspace_manager();
1104 
1105 	spin_lock_init(&compr_pool.lock);
1106 	INIT_LIST_HEAD(&compr_pool.list);
1107 	compr_pool.count = 0;
1108 	/* 128K / 4K = 32, for 8 threads is 256 pages. */
1109 	compr_pool.thresh = BTRFS_MAX_COMPRESSED / PAGE_SIZE * 8;
1110 	compr_pool.shrinker->count_objects = btrfs_compr_pool_count;
1111 	compr_pool.shrinker->scan_objects = btrfs_compr_pool_scan;
1112 	compr_pool.shrinker->batch = 32;
1113 	compr_pool.shrinker->seeks = DEFAULT_SEEKS;
1114 	shrinker_register(compr_pool.shrinker);
1115 
1116 	return 0;
1117 }
1118 
btrfs_exit_compress(void)1119 void __cold btrfs_exit_compress(void)
1120 {
1121 	/* For now scan drains all pages and does not touch the parameters. */
1122 	btrfs_compr_pool_scan(NULL, NULL);
1123 	shrinker_free(compr_pool.shrinker);
1124 
1125 	btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_NONE);
1126 	btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_ZLIB);
1127 	btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_LZO);
1128 	zstd_cleanup_workspace_manager();
1129 	bioset_exit(&btrfs_compressed_bioset);
1130 }
1131 
1132 /*
1133  * Copy decompressed data from working buffer to pages.
1134  *
1135  * @buf:		The decompressed data buffer
1136  * @buf_len:		The decompressed data length
1137  * @decompressed:	Number of bytes that are already decompressed inside the
1138  * 			compressed extent
1139  * @cb:			The compressed extent descriptor
1140  * @orig_bio:		The original bio that the caller wants to read for
1141  *
1142  * An easier to understand graph is like below:
1143  *
1144  * 		|<- orig_bio ->|     |<- orig_bio->|
1145  * 	|<-------      full decompressed extent      ----->|
1146  * 	|<-----------    @cb range   ---->|
1147  * 	|			|<-- @buf_len -->|
1148  * 	|<--- @decompressed --->|
1149  *
1150  * Note that, @cb can be a subpage of the full decompressed extent, but
1151  * @cb->start always has the same as the orig_file_offset value of the full
1152  * decompressed extent.
1153  *
1154  * When reading compressed extent, we have to read the full compressed extent,
1155  * while @orig_bio may only want part of the range.
1156  * Thus this function will ensure only data covered by @orig_bio will be copied
1157  * to.
1158  *
1159  * Return 0 if we have copied all needed contents for @orig_bio.
1160  * Return >0 if we need continue decompress.
1161  */
btrfs_decompress_buf2page(const char * buf,u32 buf_len,struct compressed_bio * cb,u32 decompressed)1162 int btrfs_decompress_buf2page(const char *buf, u32 buf_len,
1163 			      struct compressed_bio *cb, u32 decompressed)
1164 {
1165 	struct bio *orig_bio = &cb->orig_bbio->bio;
1166 	/* Offset inside the full decompressed extent */
1167 	u32 cur_offset;
1168 
1169 	cur_offset = decompressed;
1170 	/* The main loop to do the copy */
1171 	while (cur_offset < decompressed + buf_len) {
1172 		struct bio_vec bvec;
1173 		size_t copy_len;
1174 		u32 copy_start;
1175 		/* Offset inside the full decompressed extent */
1176 		u32 bvec_offset;
1177 
1178 		bvec = bio_iter_iovec(orig_bio, orig_bio->bi_iter);
1179 		/*
1180 		 * cb->start may underflow, but subtracting that value can still
1181 		 * give us correct offset inside the full decompressed extent.
1182 		 */
1183 		bvec_offset = page_offset(bvec.bv_page) + bvec.bv_offset - cb->start;
1184 
1185 		/* Haven't reached the bvec range, exit */
1186 		if (decompressed + buf_len <= bvec_offset)
1187 			return 1;
1188 
1189 		copy_start = max(cur_offset, bvec_offset);
1190 		copy_len = min(bvec_offset + bvec.bv_len,
1191 			       decompressed + buf_len) - copy_start;
1192 		ASSERT(copy_len);
1193 
1194 		/*
1195 		 * Extra range check to ensure we didn't go beyond
1196 		 * @buf + @buf_len.
1197 		 */
1198 		ASSERT(copy_start - decompressed < buf_len);
1199 		memcpy_to_page(bvec.bv_page, bvec.bv_offset,
1200 			       buf + copy_start - decompressed, copy_len);
1201 		cur_offset += copy_len;
1202 
1203 		bio_advance(orig_bio, copy_len);
1204 		/* Finished the bio */
1205 		if (!orig_bio->bi_iter.bi_size)
1206 			return 0;
1207 	}
1208 	return 1;
1209 }
1210 
1211 /*
1212  * Shannon Entropy calculation
1213  *
1214  * Pure byte distribution analysis fails to determine compressibility of data.
1215  * Try calculating entropy to estimate the average minimum number of bits
1216  * needed to encode the sampled data.
1217  *
1218  * For convenience, return the percentage of needed bits, instead of amount of
1219  * bits directly.
1220  *
1221  * @ENTROPY_LVL_ACEPTABLE - below that threshold, sample has low byte entropy
1222  *			    and can be compressible with high probability
1223  *
1224  * @ENTROPY_LVL_HIGH - data are not compressible with high probability
1225  *
1226  * Use of ilog2() decreases precision, we lower the LVL to 5 to compensate.
1227  */
1228 #define ENTROPY_LVL_ACEPTABLE		(65)
1229 #define ENTROPY_LVL_HIGH		(80)
1230 
1231 /*
1232  * For increasead precision in shannon_entropy calculation,
1233  * let's do pow(n, M) to save more digits after comma:
1234  *
1235  * - maximum int bit length is 64
1236  * - ilog2(MAX_SAMPLE_SIZE)	-> 13
1237  * - 13 * 4 = 52 < 64		-> M = 4
1238  *
1239  * So use pow(n, 4).
1240  */
ilog2_w(u64 n)1241 static inline u32 ilog2_w(u64 n)
1242 {
1243 	return ilog2(n * n * n * n);
1244 }
1245 
shannon_entropy(struct heuristic_ws * ws)1246 static u32 shannon_entropy(struct heuristic_ws *ws)
1247 {
1248 	const u32 entropy_max = 8 * ilog2_w(2);
1249 	u32 entropy_sum = 0;
1250 	u32 p, p_base, sz_base;
1251 	u32 i;
1252 
1253 	sz_base = ilog2_w(ws->sample_size);
1254 	for (i = 0; i < BUCKET_SIZE && ws->bucket[i].count > 0; i++) {
1255 		p = ws->bucket[i].count;
1256 		p_base = ilog2_w(p);
1257 		entropy_sum += p * (sz_base - p_base);
1258 	}
1259 
1260 	entropy_sum /= ws->sample_size;
1261 	return entropy_sum * 100 / entropy_max;
1262 }
1263 
1264 #define RADIX_BASE		4U
1265 #define COUNTERS_SIZE		(1U << RADIX_BASE)
1266 
get4bits(u64 num,int shift)1267 static u8 get4bits(u64 num, int shift) {
1268 	u8 low4bits;
1269 
1270 	num >>= shift;
1271 	/* Reverse order */
1272 	low4bits = (COUNTERS_SIZE - 1) - (num % COUNTERS_SIZE);
1273 	return low4bits;
1274 }
1275 
1276 /*
1277  * Use 4 bits as radix base
1278  * Use 16 u32 counters for calculating new position in buf array
1279  *
1280  * @array     - array that will be sorted
1281  * @array_buf - buffer array to store sorting results
1282  *              must be equal in size to @array
1283  * @num       - array size
1284  */
radix_sort(struct bucket_item * array,struct bucket_item * array_buf,int num)1285 static void radix_sort(struct bucket_item *array, struct bucket_item *array_buf,
1286 		       int num)
1287 {
1288 	u64 max_num;
1289 	u64 buf_num;
1290 	u32 counters[COUNTERS_SIZE];
1291 	u32 new_addr;
1292 	u32 addr;
1293 	int bitlen;
1294 	int shift;
1295 	int i;
1296 
1297 	/*
1298 	 * Try avoid useless loop iterations for small numbers stored in big
1299 	 * counters.  Example: 48 33 4 ... in 64bit array
1300 	 */
1301 	max_num = array[0].count;
1302 	for (i = 1; i < num; i++) {
1303 		buf_num = array[i].count;
1304 		if (buf_num > max_num)
1305 			max_num = buf_num;
1306 	}
1307 
1308 	buf_num = ilog2(max_num);
1309 	bitlen = ALIGN(buf_num, RADIX_BASE * 2);
1310 
1311 	shift = 0;
1312 	while (shift < bitlen) {
1313 		memset(counters, 0, sizeof(counters));
1314 
1315 		for (i = 0; i < num; i++) {
1316 			buf_num = array[i].count;
1317 			addr = get4bits(buf_num, shift);
1318 			counters[addr]++;
1319 		}
1320 
1321 		for (i = 1; i < COUNTERS_SIZE; i++)
1322 			counters[i] += counters[i - 1];
1323 
1324 		for (i = num - 1; i >= 0; i--) {
1325 			buf_num = array[i].count;
1326 			addr = get4bits(buf_num, shift);
1327 			counters[addr]--;
1328 			new_addr = counters[addr];
1329 			array_buf[new_addr] = array[i];
1330 		}
1331 
1332 		shift += RADIX_BASE;
1333 
1334 		/*
1335 		 * Normal radix expects to move data from a temporary array, to
1336 		 * the main one.  But that requires some CPU time. Avoid that
1337 		 * by doing another sort iteration to original array instead of
1338 		 * memcpy()
1339 		 */
1340 		memset(counters, 0, sizeof(counters));
1341 
1342 		for (i = 0; i < num; i ++) {
1343 			buf_num = array_buf[i].count;
1344 			addr = get4bits(buf_num, shift);
1345 			counters[addr]++;
1346 		}
1347 
1348 		for (i = 1; i < COUNTERS_SIZE; i++)
1349 			counters[i] += counters[i - 1];
1350 
1351 		for (i = num - 1; i >= 0; i--) {
1352 			buf_num = array_buf[i].count;
1353 			addr = get4bits(buf_num, shift);
1354 			counters[addr]--;
1355 			new_addr = counters[addr];
1356 			array[new_addr] = array_buf[i];
1357 		}
1358 
1359 		shift += RADIX_BASE;
1360 	}
1361 }
1362 
1363 /*
1364  * Size of the core byte set - how many bytes cover 90% of the sample
1365  *
1366  * There are several types of structured binary data that use nearly all byte
1367  * values. The distribution can be uniform and counts in all buckets will be
1368  * nearly the same (eg. encrypted data). Unlikely to be compressible.
1369  *
1370  * Other possibility is normal (Gaussian) distribution, where the data could
1371  * be potentially compressible, but we have to take a few more steps to decide
1372  * how much.
1373  *
1374  * @BYTE_CORE_SET_LOW  - main part of byte values repeated frequently,
1375  *                       compression algo can easy fix that
1376  * @BYTE_CORE_SET_HIGH - data have uniform distribution and with high
1377  *                       probability is not compressible
1378  */
1379 #define BYTE_CORE_SET_LOW		(64)
1380 #define BYTE_CORE_SET_HIGH		(200)
1381 
byte_core_set_size(struct heuristic_ws * ws)1382 static int byte_core_set_size(struct heuristic_ws *ws)
1383 {
1384 	u32 i;
1385 	u32 coreset_sum = 0;
1386 	const u32 core_set_threshold = ws->sample_size * 90 / 100;
1387 	struct bucket_item *bucket = ws->bucket;
1388 
1389 	/* Sort in reverse order */
1390 	radix_sort(ws->bucket, ws->bucket_b, BUCKET_SIZE);
1391 
1392 	for (i = 0; i < BYTE_CORE_SET_LOW; i++)
1393 		coreset_sum += bucket[i].count;
1394 
1395 	if (coreset_sum > core_set_threshold)
1396 		return i;
1397 
1398 	for (; i < BYTE_CORE_SET_HIGH && bucket[i].count > 0; i++) {
1399 		coreset_sum += bucket[i].count;
1400 		if (coreset_sum > core_set_threshold)
1401 			break;
1402 	}
1403 
1404 	return i;
1405 }
1406 
1407 /*
1408  * Count byte values in buckets.
1409  * This heuristic can detect textual data (configs, xml, json, html, etc).
1410  * Because in most text-like data byte set is restricted to limited number of
1411  * possible characters, and that restriction in most cases makes data easy to
1412  * compress.
1413  *
1414  * @BYTE_SET_THRESHOLD - consider all data within this byte set size:
1415  *	less - compressible
1416  *	more - need additional analysis
1417  */
1418 #define BYTE_SET_THRESHOLD		(64)
1419 
byte_set_size(const struct heuristic_ws * ws)1420 static u32 byte_set_size(const struct heuristic_ws *ws)
1421 {
1422 	u32 i;
1423 	u32 byte_set_size = 0;
1424 
1425 	for (i = 0; i < BYTE_SET_THRESHOLD; i++) {
1426 		if (ws->bucket[i].count > 0)
1427 			byte_set_size++;
1428 	}
1429 
1430 	/*
1431 	 * Continue collecting count of byte values in buckets.  If the byte
1432 	 * set size is bigger then the threshold, it's pointless to continue,
1433 	 * the detection technique would fail for this type of data.
1434 	 */
1435 	for (; i < BUCKET_SIZE; i++) {
1436 		if (ws->bucket[i].count > 0) {
1437 			byte_set_size++;
1438 			if (byte_set_size > BYTE_SET_THRESHOLD)
1439 				return byte_set_size;
1440 		}
1441 	}
1442 
1443 	return byte_set_size;
1444 }
1445 
sample_repeated_patterns(struct heuristic_ws * ws)1446 static bool sample_repeated_patterns(struct heuristic_ws *ws)
1447 {
1448 	const u32 half_of_sample = ws->sample_size / 2;
1449 	const u8 *data = ws->sample;
1450 
1451 	return memcmp(&data[0], &data[half_of_sample], half_of_sample) == 0;
1452 }
1453 
heuristic_collect_sample(struct inode * inode,u64 start,u64 end,struct heuristic_ws * ws)1454 static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end,
1455 				     struct heuristic_ws *ws)
1456 {
1457 	struct page *page;
1458 	u64 index, index_end;
1459 	u32 i, curr_sample_pos;
1460 	u8 *in_data;
1461 
1462 	/*
1463 	 * Compression handles the input data by chunks of 128KiB
1464 	 * (defined by BTRFS_MAX_UNCOMPRESSED)
1465 	 *
1466 	 * We do the same for the heuristic and loop over the whole range.
1467 	 *
1468 	 * MAX_SAMPLE_SIZE - calculated under assumption that heuristic will
1469 	 * process no more than BTRFS_MAX_UNCOMPRESSED at a time.
1470 	 */
1471 	if (end - start > BTRFS_MAX_UNCOMPRESSED)
1472 		end = start + BTRFS_MAX_UNCOMPRESSED;
1473 
1474 	index = start >> PAGE_SHIFT;
1475 	index_end = end >> PAGE_SHIFT;
1476 
1477 	/* Don't miss unaligned end */
1478 	if (!PAGE_ALIGNED(end))
1479 		index_end++;
1480 
1481 	curr_sample_pos = 0;
1482 	while (index < index_end) {
1483 		page = find_get_page(inode->i_mapping, index);
1484 		in_data = kmap_local_page(page);
1485 		/* Handle case where the start is not aligned to PAGE_SIZE */
1486 		i = start % PAGE_SIZE;
1487 		while (i < PAGE_SIZE - SAMPLING_READ_SIZE) {
1488 			/* Don't sample any garbage from the last page */
1489 			if (start > end - SAMPLING_READ_SIZE)
1490 				break;
1491 			memcpy(&ws->sample[curr_sample_pos], &in_data[i],
1492 					SAMPLING_READ_SIZE);
1493 			i += SAMPLING_INTERVAL;
1494 			start += SAMPLING_INTERVAL;
1495 			curr_sample_pos += SAMPLING_READ_SIZE;
1496 		}
1497 		kunmap_local(in_data);
1498 		put_page(page);
1499 
1500 		index++;
1501 	}
1502 
1503 	ws->sample_size = curr_sample_pos;
1504 }
1505 
1506 /*
1507  * Compression heuristic.
1508  *
1509  * The following types of analysis can be performed:
1510  * - detect mostly zero data
1511  * - detect data with low "byte set" size (text, etc)
1512  * - detect data with low/high "core byte" set
1513  *
1514  * Return non-zero if the compression should be done, 0 otherwise.
1515  */
btrfs_compress_heuristic(struct btrfs_inode * inode,u64 start,u64 end)1516 int btrfs_compress_heuristic(struct btrfs_inode *inode, u64 start, u64 end)
1517 {
1518 	struct list_head *ws_list = get_workspace(0, 0);
1519 	struct heuristic_ws *ws;
1520 	u32 i;
1521 	u8 byte;
1522 	int ret = 0;
1523 
1524 	ws = list_entry(ws_list, struct heuristic_ws, list);
1525 
1526 	heuristic_collect_sample(&inode->vfs_inode, start, end, ws);
1527 
1528 	if (sample_repeated_patterns(ws)) {
1529 		ret = 1;
1530 		goto out;
1531 	}
1532 
1533 	memset(ws->bucket, 0, sizeof(*ws->bucket)*BUCKET_SIZE);
1534 
1535 	for (i = 0; i < ws->sample_size; i++) {
1536 		byte = ws->sample[i];
1537 		ws->bucket[byte].count++;
1538 	}
1539 
1540 	i = byte_set_size(ws);
1541 	if (i < BYTE_SET_THRESHOLD) {
1542 		ret = 2;
1543 		goto out;
1544 	}
1545 
1546 	i = byte_core_set_size(ws);
1547 	if (i <= BYTE_CORE_SET_LOW) {
1548 		ret = 3;
1549 		goto out;
1550 	}
1551 
1552 	if (i >= BYTE_CORE_SET_HIGH) {
1553 		ret = 0;
1554 		goto out;
1555 	}
1556 
1557 	i = shannon_entropy(ws);
1558 	if (i <= ENTROPY_LVL_ACEPTABLE) {
1559 		ret = 4;
1560 		goto out;
1561 	}
1562 
1563 	/*
1564 	 * For the levels below ENTROPY_LVL_HIGH, additional analysis would be
1565 	 * needed to give green light to compression.
1566 	 *
1567 	 * For now just assume that compression at that level is not worth the
1568 	 * resources because:
1569 	 *
1570 	 * 1. it is possible to defrag the data later
1571 	 *
1572 	 * 2. the data would turn out to be hardly compressible, eg. 150 byte
1573 	 * values, every bucket has counter at level ~54. The heuristic would
1574 	 * be confused. This can happen when data have some internal repeated
1575 	 * patterns like "abbacbbc...". This can be detected by analyzing
1576 	 * pairs of bytes, which is too costly.
1577 	 */
1578 	if (i < ENTROPY_LVL_HIGH) {
1579 		ret = 5;
1580 		goto out;
1581 	} else {
1582 		ret = 0;
1583 		goto out;
1584 	}
1585 
1586 out:
1587 	put_workspace(0, ws_list);
1588 	return ret;
1589 }
1590 
1591 /*
1592  * Convert the compression suffix (eg. after "zlib" starting with ":") to
1593  * level, unrecognized string will set the default level
1594  */
btrfs_compress_str2level(unsigned int type,const char * str)1595 unsigned int btrfs_compress_str2level(unsigned int type, const char *str)
1596 {
1597 	unsigned int level = 0;
1598 	int ret;
1599 
1600 	if (!type)
1601 		return 0;
1602 
1603 	if (str[0] == ':') {
1604 		ret = kstrtouint(str + 1, 10, &level);
1605 		if (ret)
1606 			level = 0;
1607 	}
1608 
1609 	level = btrfs_compress_set_level(type, level);
1610 
1611 	return level;
1612 }
1613