1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * fs/mpage.c
4 *
5 * Copyright (C) 2002, Linus Torvalds.
6 *
7 * Contains functions related to preparing and submitting BIOs which contain
8 * multiple pagecache pages.
9 *
10 * 15May2002 Andrew Morton
11 * Initial version
12 * 27Jun2002 axboe@suse.de
13 * use bio_add_page() to build bio's just the right size
14 */
15
16 #include <linux/kernel.h>
17 #include <linux/export.h>
18 #include <linux/mm.h>
19 #include <linux/kdev_t.h>
20 #include <linux/gfp.h>
21 #include <linux/bio.h>
22 #include <linux/fs.h>
23 #include <linux/buffer_head.h>
24 #include <linux/blkdev.h>
25 #include <linux/highmem.h>
26 #include <linux/prefetch.h>
27 #include <linux/mpage.h>
28 #include <linux/mm_inline.h>
29 #include <linux/writeback.h>
30 #include <linux/backing-dev.h>
31 #include <linux/pagevec.h>
32 #include <linux/cleancache.h>
33 #include "internal.h"
34
35 /*
36 * I/O completion handler for multipage BIOs.
37 *
38 * The mpage code never puts partial pages into a BIO (except for end-of-file).
39 * If a page does not map to a contiguous run of blocks then it simply falls
40 * back to block_read_full_folio().
41 *
42 * Why is this? If a page's completion depends on a number of different BIOs
43 * which can complete in any order (or at the same time) then determining the
44 * status of that page is hard. See end_buffer_async_read() for the details.
45 * There is no point in duplicating all that complexity.
46 */
mpage_read_end_io(struct bio * bio)47 static void mpage_read_end_io(struct bio *bio)
48 {
49 struct folio_iter fi;
50 int err = blk_status_to_errno(bio->bi_status);
51
52 bio_for_each_folio_all(fi, bio)
53 folio_end_read(fi.folio, err == 0);
54
55 bio_put(bio);
56 }
57
mpage_write_end_io(struct bio * bio)58 static void mpage_write_end_io(struct bio *bio)
59 {
60 struct folio_iter fi;
61 int err = blk_status_to_errno(bio->bi_status);
62
63 bio_for_each_folio_all(fi, bio) {
64 if (err)
65 mapping_set_error(fi.folio->mapping, err);
66 folio_end_writeback(fi.folio);
67 }
68
69 bio_put(bio);
70 }
71
mpage_bio_submit_read(struct bio * bio)72 static struct bio *mpage_bio_submit_read(struct bio *bio)
73 {
74 bio->bi_end_io = mpage_read_end_io;
75 guard_bio_eod(bio);
76 submit_bio(bio);
77 return NULL;
78 }
79
mpage_bio_submit_write(struct bio * bio)80 static struct bio *mpage_bio_submit_write(struct bio *bio)
81 {
82 bio->bi_end_io = mpage_write_end_io;
83 guard_bio_eod(bio);
84 submit_bio(bio);
85 return NULL;
86 }
87
88 /*
89 * support function for mpage_readahead. The fs supplied get_block might
90 * return an up to date buffer. This is used to map that buffer into
91 * the page, which allows read_folio to avoid triggering a duplicate call
92 * to get_block.
93 *
94 * The idea is to avoid adding buffers to pages that don't already have
95 * them. So when the buffer is up to date and the page size == block size,
96 * this marks the page up to date instead of adding new buffers.
97 */
map_buffer_to_folio(struct folio * folio,struct buffer_head * bh,int page_block)98 static void map_buffer_to_folio(struct folio *folio, struct buffer_head *bh,
99 int page_block)
100 {
101 struct inode *inode = folio->mapping->host;
102 struct buffer_head *page_bh, *head;
103 int block = 0;
104
105 head = folio_buffers(folio);
106 if (!head) {
107 /*
108 * don't make any buffers if there is only one buffer on
109 * the folio and the folio just needs to be set up to date
110 */
111 if (inode->i_blkbits == PAGE_SHIFT &&
112 buffer_uptodate(bh)) {
113 folio_mark_uptodate(folio);
114 return;
115 }
116 head = create_empty_buffers(folio, i_blocksize(inode), 0);
117 }
118
119 page_bh = head;
120 do {
121 if (block == page_block) {
122 page_bh->b_state = bh->b_state;
123 page_bh->b_bdev = bh->b_bdev;
124 page_bh->b_blocknr = bh->b_blocknr;
125 break;
126 }
127 page_bh = page_bh->b_this_page;
128 block++;
129 } while (page_bh != head);
130 }
131
132 struct mpage_readpage_args {
133 struct bio *bio;
134 struct folio *folio;
135 unsigned int nr_pages;
136 bool is_readahead;
137 sector_t last_block_in_bio;
138 struct buffer_head map_bh;
139 unsigned long first_logical_block;
140 get_block_t *get_block;
141 };
142
143 /*
144 * This is the worker routine which does all the work of mapping the disk
145 * blocks and constructs largest possible bios, submits them for IO if the
146 * blocks are not contiguous on the disk.
147 *
148 * We pass a buffer_head back and forth and use its buffer_mapped() flag to
149 * represent the validity of its disk mapping and to decide when to do the next
150 * get_block() call.
151 */
do_mpage_readpage(struct mpage_readpage_args * args)152 static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
153 {
154 struct folio *folio = args->folio;
155 struct inode *inode = folio->mapping->host;
156 const unsigned blkbits = inode->i_blkbits;
157 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
158 const unsigned blocksize = 1 << blkbits;
159 struct buffer_head *map_bh = &args->map_bh;
160 sector_t block_in_file;
161 sector_t last_block;
162 sector_t last_block_in_file;
163 sector_t first_block;
164 unsigned page_block;
165 unsigned first_hole = blocks_per_page;
166 struct block_device *bdev = NULL;
167 int length;
168 int fully_mapped = 1;
169 blk_opf_t opf = REQ_OP_READ;
170 unsigned nblocks;
171 unsigned relative_block;
172 gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
173
174 /* MAX_BUF_PER_PAGE, for example */
175 VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
176
177 if (args->is_readahead) {
178 opf |= REQ_RAHEAD;
179 gfp |= __GFP_NORETRY | __GFP_NOWARN;
180 }
181
182 if (folio_buffers(folio))
183 goto confused;
184
185 block_in_file = (sector_t)folio->index << (PAGE_SHIFT - blkbits);
186 last_block = block_in_file + args->nr_pages * blocks_per_page;
187 last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
188 if (last_block > last_block_in_file)
189 last_block = last_block_in_file;
190 page_block = 0;
191
192 /*
193 * Map blocks using the result from the previous get_blocks call first.
194 */
195 nblocks = map_bh->b_size >> blkbits;
196 if (buffer_mapped(map_bh) &&
197 block_in_file > args->first_logical_block &&
198 block_in_file < (args->first_logical_block + nblocks)) {
199 unsigned map_offset = block_in_file - args->first_logical_block;
200 unsigned last = nblocks - map_offset;
201
202 first_block = map_bh->b_blocknr + map_offset;
203 for (relative_block = 0; ; relative_block++) {
204 if (relative_block == last) {
205 clear_buffer_mapped(map_bh);
206 break;
207 }
208 if (page_block == blocks_per_page)
209 break;
210 page_block++;
211 block_in_file++;
212 }
213 bdev = map_bh->b_bdev;
214 }
215
216 /*
217 * Then do more get_blocks calls until we are done with this folio.
218 */
219 map_bh->b_folio = folio;
220 while (page_block < blocks_per_page) {
221 map_bh->b_state = 0;
222 map_bh->b_size = 0;
223
224 if (block_in_file < last_block) {
225 map_bh->b_size = (last_block-block_in_file) << blkbits;
226 if (args->get_block(inode, block_in_file, map_bh, 0))
227 goto confused;
228 args->first_logical_block = block_in_file;
229 }
230
231 if (!buffer_mapped(map_bh)) {
232 fully_mapped = 0;
233 if (first_hole == blocks_per_page)
234 first_hole = page_block;
235 page_block++;
236 block_in_file++;
237 continue;
238 }
239
240 /* some filesystems will copy data into the page during
241 * the get_block call, in which case we don't want to
242 * read it again. map_buffer_to_folio copies the data
243 * we just collected from get_block into the folio's buffers
244 * so read_folio doesn't have to repeat the get_block call
245 */
246 if (buffer_uptodate(map_bh)) {
247 map_buffer_to_folio(folio, map_bh, page_block);
248 goto confused;
249 }
250
251 if (first_hole != blocks_per_page)
252 goto confused; /* hole -> non-hole */
253
254 /* Contiguous blocks? */
255 if (!page_block)
256 first_block = map_bh->b_blocknr;
257 else if (first_block + page_block != map_bh->b_blocknr)
258 goto confused;
259 nblocks = map_bh->b_size >> blkbits;
260 for (relative_block = 0; ; relative_block++) {
261 if (relative_block == nblocks) {
262 clear_buffer_mapped(map_bh);
263 break;
264 } else if (page_block == blocks_per_page)
265 break;
266 page_block++;
267 block_in_file++;
268 }
269 bdev = map_bh->b_bdev;
270 }
271
272 if (first_hole != blocks_per_page) {
273 folio_zero_segment(folio, first_hole << blkbits, PAGE_SIZE);
274 if (first_hole == 0) {
275 folio_mark_uptodate(folio);
276 folio_unlock(folio);
277 goto out;
278 }
279 } else if (fully_mapped) {
280 folio_set_mappedtodisk(folio);
281 }
282
283 if (fully_mapped && blocks_per_page == 1 && !folio_test_uptodate(folio) &&
284 cleancache_get_page(&folio->page) == 0) {
285 folio_mark_uptodate(folio);
286 goto confused;
287 }
288
289 /*
290 * This folio will go to BIO. Do we need to send this BIO off first?
291 */
292 if (args->bio && (args->last_block_in_bio != first_block - 1))
293 args->bio = mpage_bio_submit_read(args->bio);
294
295 alloc_new:
296 if (args->bio == NULL) {
297 args->bio = bio_alloc(bdev, bio_max_segs(args->nr_pages), opf,
298 gfp);
299 if (args->bio == NULL)
300 goto confused;
301 args->bio->bi_iter.bi_sector = first_block << (blkbits - 9);
302 }
303
304 length = first_hole << blkbits;
305 if (!bio_add_folio(args->bio, folio, length, 0)) {
306 args->bio = mpage_bio_submit_read(args->bio);
307 goto alloc_new;
308 }
309
310 relative_block = block_in_file - args->first_logical_block;
311 nblocks = map_bh->b_size >> blkbits;
312 if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
313 (first_hole != blocks_per_page))
314 args->bio = mpage_bio_submit_read(args->bio);
315 else
316 args->last_block_in_bio = first_block + blocks_per_page - 1;
317 out:
318 return args->bio;
319
320 confused:
321 if (args->bio)
322 args->bio = mpage_bio_submit_read(args->bio);
323 if (!folio_test_uptodate(folio))
324 block_read_full_folio(folio, args->get_block);
325 else
326 folio_unlock(folio);
327 goto out;
328 }
329
330 /**
331 * mpage_readahead - start reads against pages
332 * @rac: Describes which pages to read.
333 * @get_block: The filesystem's block mapper function.
334 *
335 * This function walks the pages and the blocks within each page, building and
336 * emitting large BIOs.
337 *
338 * If anything unusual happens, such as:
339 *
340 * - encountering a page which has buffers
341 * - encountering a page which has a non-hole after a hole
342 * - encountering a page with non-contiguous blocks
343 *
344 * then this code just gives up and calls the buffer_head-based read function.
345 * It does handle a page which has holes at the end - that is a common case:
346 * the end-of-file on blocksize < PAGE_SIZE setups.
347 *
348 * BH_Boundary explanation:
349 *
350 * There is a problem. The mpage read code assembles several pages, gets all
351 * their disk mappings, and then submits them all. That's fine, but obtaining
352 * the disk mappings may require I/O. Reads of indirect blocks, for example.
353 *
354 * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
355 * submitted in the following order:
356 *
357 * 12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
358 *
359 * because the indirect block has to be read to get the mappings of blocks
360 * 13,14,15,16. Obviously, this impacts performance.
361 *
362 * So what we do it to allow the filesystem's get_block() function to set
363 * BH_Boundary when it maps block 11. BH_Boundary says: mapping of the block
364 * after this one will require I/O against a block which is probably close to
365 * this one. So you should push what I/O you have currently accumulated.
366 *
367 * This all causes the disk requests to be issued in the correct order.
368 */
mpage_readahead(struct readahead_control * rac,get_block_t get_block)369 void mpage_readahead(struct readahead_control *rac, get_block_t get_block)
370 {
371 struct folio *folio;
372 struct mpage_readpage_args args = {
373 .get_block = get_block,
374 .is_readahead = true,
375 };
376
377 while ((folio = readahead_folio(rac))) {
378 prefetchw(&folio->flags);
379 args.folio = folio;
380 args.nr_pages = readahead_count(rac);
381 args.bio = do_mpage_readpage(&args);
382 }
383 if (args.bio)
384 mpage_bio_submit_read(args.bio);
385 }
386 EXPORT_SYMBOL(mpage_readahead);
387
388 /*
389 * This isn't called much at all
390 */
mpage_read_folio(struct folio * folio,get_block_t get_block)391 int mpage_read_folio(struct folio *folio, get_block_t get_block)
392 {
393 struct mpage_readpage_args args = {
394 .folio = folio,
395 .nr_pages = 1,
396 .get_block = get_block,
397 };
398
399 args.bio = do_mpage_readpage(&args);
400 if (args.bio)
401 mpage_bio_submit_read(args.bio);
402 return 0;
403 }
404 EXPORT_SYMBOL(mpage_read_folio);
405
406 /*
407 * Writing is not so simple.
408 *
409 * If the page has buffers then they will be used for obtaining the disk
410 * mapping. We only support pages which are fully mapped-and-dirty, with a
411 * special case for pages which are unmapped at the end: end-of-file.
412 *
413 * If the page has no buffers (preferred) then the page is mapped here.
414 *
415 * If all blocks are found to be contiguous then the page can go into the
416 * BIO. Otherwise fall back to the mapping's writepage().
417 *
418 * FIXME: This code wants an estimate of how many pages are still to be
419 * written, so it can intelligently allocate a suitably-sized BIO. For now,
420 * just allocate full-size (16-page) BIOs.
421 */
422
423 struct mpage_data {
424 struct bio *bio;
425 sector_t last_block_in_bio;
426 get_block_t *get_block;
427 };
428
429 /*
430 * We have our BIO, so we can now mark the buffers clean. Make
431 * sure to only clean buffers which we know we'll be writing.
432 */
clean_buffers(struct folio * folio,unsigned first_unmapped)433 static void clean_buffers(struct folio *folio, unsigned first_unmapped)
434 {
435 unsigned buffer_counter = 0;
436 struct buffer_head *bh, *head = folio_buffers(folio);
437
438 if (!head)
439 return;
440 bh = head;
441
442 do {
443 if (buffer_counter++ == first_unmapped)
444 break;
445 clear_buffer_dirty(bh);
446 bh = bh->b_this_page;
447 } while (bh != head);
448
449 /*
450 * we cannot drop the bh if the page is not uptodate or a concurrent
451 * read_folio would fail to serialize with the bh and it would read from
452 * disk before we reach the platter.
453 */
454 if (buffer_heads_over_limit && folio_test_uptodate(folio))
455 try_to_free_buffers(folio);
456 }
457
__mpage_writepage(struct folio * folio,struct writeback_control * wbc,void * data)458 static int __mpage_writepage(struct folio *folio, struct writeback_control *wbc,
459 void *data)
460 {
461 struct mpage_data *mpd = data;
462 struct bio *bio = mpd->bio;
463 struct address_space *mapping = folio->mapping;
464 struct inode *inode = mapping->host;
465 const unsigned blkbits = inode->i_blkbits;
466 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
467 sector_t last_block;
468 sector_t block_in_file;
469 sector_t first_block;
470 unsigned page_block;
471 unsigned first_unmapped = blocks_per_page;
472 struct block_device *bdev = NULL;
473 int boundary = 0;
474 sector_t boundary_block = 0;
475 struct block_device *boundary_bdev = NULL;
476 size_t length;
477 struct buffer_head map_bh;
478 loff_t i_size = i_size_read(inode);
479 int ret = 0;
480 struct buffer_head *head = folio_buffers(folio);
481
482 if (head) {
483 struct buffer_head *bh = head;
484
485 /* If they're all mapped and dirty, do it */
486 page_block = 0;
487 do {
488 BUG_ON(buffer_locked(bh));
489 if (!buffer_mapped(bh)) {
490 /*
491 * unmapped dirty buffers are created by
492 * block_dirty_folio -> mmapped data
493 */
494 if (buffer_dirty(bh))
495 goto confused;
496 if (first_unmapped == blocks_per_page)
497 first_unmapped = page_block;
498 continue;
499 }
500
501 if (first_unmapped != blocks_per_page)
502 goto confused; /* hole -> non-hole */
503
504 if (!buffer_dirty(bh) || !buffer_uptodate(bh))
505 goto confused;
506 if (page_block) {
507 if (bh->b_blocknr != first_block + page_block)
508 goto confused;
509 } else {
510 first_block = bh->b_blocknr;
511 }
512 page_block++;
513 boundary = buffer_boundary(bh);
514 if (boundary) {
515 boundary_block = bh->b_blocknr;
516 boundary_bdev = bh->b_bdev;
517 }
518 bdev = bh->b_bdev;
519 } while ((bh = bh->b_this_page) != head);
520
521 if (first_unmapped)
522 goto page_is_mapped;
523
524 /*
525 * Page has buffers, but they are all unmapped. The page was
526 * created by pagein or read over a hole which was handled by
527 * block_read_full_folio(). If this address_space is also
528 * using mpage_readahead then this can rarely happen.
529 */
530 goto confused;
531 }
532
533 /*
534 * The page has no buffers: map it to disk
535 */
536 BUG_ON(!folio_test_uptodate(folio));
537 block_in_file = (sector_t)folio->index << (PAGE_SHIFT - blkbits);
538 /*
539 * Whole page beyond EOF? Skip allocating blocks to avoid leaking
540 * space.
541 */
542 if (block_in_file >= (i_size + (1 << blkbits) - 1) >> blkbits)
543 goto page_is_mapped;
544 last_block = (i_size - 1) >> blkbits;
545 map_bh.b_folio = folio;
546 for (page_block = 0; page_block < blocks_per_page; ) {
547
548 map_bh.b_state = 0;
549 map_bh.b_size = 1 << blkbits;
550 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
551 goto confused;
552 if (!buffer_mapped(&map_bh))
553 goto confused;
554 if (buffer_new(&map_bh))
555 clean_bdev_bh_alias(&map_bh);
556 if (buffer_boundary(&map_bh)) {
557 boundary_block = map_bh.b_blocknr;
558 boundary_bdev = map_bh.b_bdev;
559 }
560 if (page_block) {
561 if (map_bh.b_blocknr != first_block + page_block)
562 goto confused;
563 } else {
564 first_block = map_bh.b_blocknr;
565 }
566 page_block++;
567 boundary = buffer_boundary(&map_bh);
568 bdev = map_bh.b_bdev;
569 if (block_in_file == last_block)
570 break;
571 block_in_file++;
572 }
573 BUG_ON(page_block == 0);
574
575 first_unmapped = page_block;
576
577 page_is_mapped:
578 /* Don't bother writing beyond EOF, truncate will discard the folio */
579 if (folio_pos(folio) >= i_size)
580 goto confused;
581 length = folio_size(folio);
582 if (folio_pos(folio) + length > i_size) {
583 /*
584 * The page straddles i_size. It must be zeroed out on each
585 * and every writepage invocation because it may be mmapped.
586 * "A file is mapped in multiples of the page size. For a file
587 * that is not a multiple of the page size, the remaining memory
588 * is zeroed when mapped, and writes to that region are not
589 * written out to the file."
590 */
591 length = i_size - folio_pos(folio);
592 folio_zero_segment(folio, length, folio_size(folio));
593 }
594
595 /*
596 * This page will go to BIO. Do we need to send this BIO off first?
597 */
598 if (bio && mpd->last_block_in_bio != first_block - 1)
599 bio = mpage_bio_submit_write(bio);
600
601 alloc_new:
602 if (bio == NULL) {
603 bio = bio_alloc(bdev, BIO_MAX_VECS,
604 REQ_OP_WRITE | wbc_to_write_flags(wbc),
605 GFP_NOFS);
606 bio->bi_iter.bi_sector = first_block << (blkbits - 9);
607 wbc_init_bio(wbc, bio);
608 bio->bi_write_hint = inode->i_write_hint;
609 }
610
611 /*
612 * Must try to add the page before marking the buffer clean or
613 * the confused fail path above (OOM) will be very confused when
614 * it finds all bh marked clean (i.e. it will not write anything)
615 */
616 wbc_account_cgroup_owner(wbc, folio, folio_size(folio));
617 length = first_unmapped << blkbits;
618 if (!bio_add_folio(bio, folio, length, 0)) {
619 bio = mpage_bio_submit_write(bio);
620 goto alloc_new;
621 }
622
623 clean_buffers(folio, first_unmapped);
624
625 BUG_ON(folio_test_writeback(folio));
626 folio_start_writeback(folio);
627 folio_unlock(folio);
628 if (boundary || (first_unmapped != blocks_per_page)) {
629 bio = mpage_bio_submit_write(bio);
630 if (boundary_block) {
631 write_boundary_block(boundary_bdev,
632 boundary_block, 1 << blkbits);
633 }
634 } else {
635 mpd->last_block_in_bio = first_block + blocks_per_page - 1;
636 }
637 goto out;
638
639 confused:
640 if (bio)
641 bio = mpage_bio_submit_write(bio);
642
643 /*
644 * The caller has a ref on the inode, so *mapping is stable
645 */
646 ret = block_write_full_folio(folio, wbc, mpd->get_block);
647 mapping_set_error(mapping, ret);
648 out:
649 mpd->bio = bio;
650 return ret;
651 }
652
653 /**
654 * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
655 * @mapping: address space structure to write
656 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
657 * @get_block: the filesystem's block mapper function.
658 *
659 * This is a library function, which implements the writepages()
660 * address_space_operation.
661 */
662 int
mpage_writepages(struct address_space * mapping,struct writeback_control * wbc,get_block_t get_block)663 mpage_writepages(struct address_space *mapping,
664 struct writeback_control *wbc, get_block_t get_block)
665 {
666 struct mpage_data mpd = {
667 .get_block = get_block,
668 };
669 struct blk_plug plug;
670 int ret;
671
672 blk_start_plug(&plug);
673 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
674 if (mpd.bio)
675 mpage_bio_submit_write(mpd.bio);
676 blk_finish_plug(&plug);
677 return ret;
678 }
679 EXPORT_SYMBOL(mpage_writepages);
680