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 "internal.h"
33
34 /*
35 * I/O completion handler for multipage BIOs.
36 *
37 * The mpage code never puts partial pages into a BIO (except for end-of-file).
38 * If a page does not map to a contiguous run of blocks then it simply falls
39 * back to block_read_full_folio().
40 *
41 * Why is this? If a page's completion depends on a number of different BIOs
42 * which can complete in any order (or at the same time) then determining the
43 * status of that page is hard. See end_buffer_async_read() for the details.
44 * There is no point in duplicating all that complexity.
45 */
mpage_read_end_io(struct bio * bio)46 static void mpage_read_end_io(struct bio *bio)
47 {
48 struct folio_iter fi;
49 int err = blk_status_to_errno(bio->bi_status);
50
51 bio_for_each_folio_all(fi, bio) {
52 if (err)
53 folio_set_error(fi.folio);
54 else
55 folio_mark_uptodate(fi.folio);
56 folio_unlock(fi.folio);
57 }
58
59 bio_put(bio);
60 }
61
mpage_write_end_io(struct bio * bio)62 static void mpage_write_end_io(struct bio *bio)
63 {
64 struct folio_iter fi;
65 int err = blk_status_to_errno(bio->bi_status);
66
67 bio_for_each_folio_all(fi, bio) {
68 if (err) {
69 folio_set_error(fi.folio);
70 mapping_set_error(fi.folio->mapping, err);
71 }
72 folio_end_writeback(fi.folio);
73 }
74
75 bio_put(bio);
76 }
77
mpage_bio_submit_read(struct bio * bio)78 static struct bio *mpage_bio_submit_read(struct bio *bio)
79 {
80 bio->bi_end_io = mpage_read_end_io;
81 guard_bio_eod(bio);
82 submit_bio(bio);
83 return NULL;
84 }
85
mpage_bio_submit_write(struct bio * bio)86 static struct bio *mpage_bio_submit_write(struct bio *bio)
87 {
88 bio->bi_end_io = mpage_write_end_io;
89 guard_bio_eod(bio);
90 submit_bio(bio);
91 return NULL;
92 }
93
94 /*
95 * support function for mpage_readahead. The fs supplied get_block might
96 * return an up to date buffer. This is used to map that buffer into
97 * the page, which allows read_folio to avoid triggering a duplicate call
98 * to get_block.
99 *
100 * The idea is to avoid adding buffers to pages that don't already have
101 * them. So when the buffer is up to date and the page size == block size,
102 * this marks the page up to date instead of adding new buffers.
103 */
map_buffer_to_folio(struct folio * folio,struct buffer_head * bh,int page_block)104 static void map_buffer_to_folio(struct folio *folio, struct buffer_head *bh,
105 int page_block)
106 {
107 struct inode *inode = folio->mapping->host;
108 struct buffer_head *page_bh, *head;
109 int block = 0;
110
111 head = folio_buffers(folio);
112 if (!head) {
113 /*
114 * don't make any buffers if there is only one buffer on
115 * the folio and the folio just needs to be set up to date
116 */
117 if (inode->i_blkbits == PAGE_SHIFT &&
118 buffer_uptodate(bh)) {
119 folio_mark_uptodate(folio);
120 return;
121 }
122 head = create_empty_buffers(folio, i_blocksize(inode), 0);
123 }
124
125 page_bh = head;
126 do {
127 if (block == page_block) {
128 page_bh->b_state = bh->b_state;
129 page_bh->b_bdev = bh->b_bdev;
130 page_bh->b_blocknr = bh->b_blocknr;
131 break;
132 }
133 page_bh = page_bh->b_this_page;
134 block++;
135 } while (page_bh != head);
136 }
137
138 struct mpage_readpage_args {
139 struct bio *bio;
140 struct folio *folio;
141 unsigned int nr_pages;
142 bool is_readahead;
143 sector_t last_block_in_bio;
144 struct buffer_head map_bh;
145 unsigned long first_logical_block;
146 get_block_t *get_block;
147 };
148
149 /*
150 * This is the worker routine which does all the work of mapping the disk
151 * blocks and constructs largest possible bios, submits them for IO if the
152 * blocks are not contiguous on the disk.
153 *
154 * We pass a buffer_head back and forth and use its buffer_mapped() flag to
155 * represent the validity of its disk mapping and to decide when to do the next
156 * get_block() call.
157 */
do_mpage_readpage(struct mpage_readpage_args * args)158 static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
159 {
160 struct folio *folio = args->folio;
161 struct inode *inode = folio->mapping->host;
162 const unsigned blkbits = inode->i_blkbits;
163 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
164 const unsigned blocksize = 1 << blkbits;
165 struct buffer_head *map_bh = &args->map_bh;
166 sector_t block_in_file;
167 sector_t last_block;
168 sector_t last_block_in_file;
169 sector_t first_block;
170 unsigned page_block;
171 unsigned first_hole = blocks_per_page;
172 struct block_device *bdev = NULL;
173 int length;
174 int fully_mapped = 1;
175 blk_opf_t opf = REQ_OP_READ;
176 unsigned nblocks;
177 unsigned relative_block;
178 gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
179
180 /* MAX_BUF_PER_PAGE, for example */
181 VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
182
183 if (args->is_readahead) {
184 opf |= REQ_RAHEAD;
185 gfp |= __GFP_NORETRY | __GFP_NOWARN;
186 }
187
188 if (folio_buffers(folio))
189 goto confused;
190
191 block_in_file = (sector_t)folio->index << (PAGE_SHIFT - blkbits);
192 last_block = block_in_file + args->nr_pages * blocks_per_page;
193 last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
194 if (last_block > last_block_in_file)
195 last_block = last_block_in_file;
196 page_block = 0;
197
198 /*
199 * Map blocks using the result from the previous get_blocks call first.
200 */
201 nblocks = map_bh->b_size >> blkbits;
202 if (buffer_mapped(map_bh) &&
203 block_in_file > args->first_logical_block &&
204 block_in_file < (args->first_logical_block + nblocks)) {
205 unsigned map_offset = block_in_file - args->first_logical_block;
206 unsigned last = nblocks - map_offset;
207
208 first_block = map_bh->b_blocknr + map_offset;
209 for (relative_block = 0; ; relative_block++) {
210 if (relative_block == last) {
211 clear_buffer_mapped(map_bh);
212 break;
213 }
214 if (page_block == blocks_per_page)
215 break;
216 page_block++;
217 block_in_file++;
218 }
219 bdev = map_bh->b_bdev;
220 }
221
222 /*
223 * Then do more get_blocks calls until we are done with this folio.
224 */
225 map_bh->b_folio = folio;
226 while (page_block < blocks_per_page) {
227 map_bh->b_state = 0;
228 map_bh->b_size = 0;
229
230 if (block_in_file < last_block) {
231 map_bh->b_size = (last_block-block_in_file) << blkbits;
232 if (args->get_block(inode, block_in_file, map_bh, 0))
233 goto confused;
234 args->first_logical_block = block_in_file;
235 }
236
237 if (!buffer_mapped(map_bh)) {
238 fully_mapped = 0;
239 if (first_hole == blocks_per_page)
240 first_hole = page_block;
241 page_block++;
242 block_in_file++;
243 continue;
244 }
245
246 /* some filesystems will copy data into the page during
247 * the get_block call, in which case we don't want to
248 * read it again. map_buffer_to_folio copies the data
249 * we just collected from get_block into the folio's buffers
250 * so read_folio doesn't have to repeat the get_block call
251 */
252 if (buffer_uptodate(map_bh)) {
253 map_buffer_to_folio(folio, map_bh, page_block);
254 goto confused;
255 }
256
257 if (first_hole != blocks_per_page)
258 goto confused; /* hole -> non-hole */
259
260 /* Contiguous blocks? */
261 if (!page_block)
262 first_block = map_bh->b_blocknr;
263 else if (first_block + page_block != map_bh->b_blocknr)
264 goto confused;
265 nblocks = map_bh->b_size >> blkbits;
266 for (relative_block = 0; ; relative_block++) {
267 if (relative_block == nblocks) {
268 clear_buffer_mapped(map_bh);
269 break;
270 } else if (page_block == blocks_per_page)
271 break;
272 page_block++;
273 block_in_file++;
274 }
275 bdev = map_bh->b_bdev;
276 }
277
278 if (first_hole != blocks_per_page) {
279 folio_zero_segment(folio, first_hole << blkbits, PAGE_SIZE);
280 if (first_hole == 0) {
281 folio_mark_uptodate(folio);
282 folio_unlock(folio);
283 goto out;
284 }
285 } else if (fully_mapped) {
286 folio_set_mappedtodisk(folio);
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->page, 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