Loading...
1/*
2 * fs/mpage.c
3 *
4 * Copyright (C) 2002, Linus Torvalds.
5 *
6 * Contains functions related to preparing and submitting BIOs which contain
7 * multiple pagecache pages.
8 *
9 * 15May2002 Andrew Morton
10 * Initial version
11 * 27Jun2002 axboe@suse.de
12 * use bio_add_page() to build bio's just the right size
13 */
14
15#include <linux/kernel.h>
16#include <linux/export.h>
17#include <linux/mm.h>
18#include <linux/kdev_t.h>
19#include <linux/gfp.h>
20#include <linux/bio.h>
21#include <linux/fs.h>
22#include <linux/buffer_head.h>
23#include <linux/blkdev.h>
24#include <linux/highmem.h>
25#include <linux/prefetch.h>
26#include <linux/mpage.h>
27#include <linux/mm_inline.h>
28#include <linux/writeback.h>
29#include <linux/backing-dev.h>
30#include <linux/pagevec.h>
31#include <linux/cleancache.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_page().
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 */
46static void mpage_end_io(struct bio *bio)
47{
48 struct bio_vec *bv;
49 int i;
50
51 bio_for_each_segment_all(bv, bio, i) {
52 struct page *page = bv->bv_page;
53 page_endio(page, bio_data_dir(bio), bio->bi_error);
54 }
55
56 bio_put(bio);
57}
58
59static struct bio *mpage_bio_submit(int rw, struct bio *bio)
60{
61 bio->bi_end_io = mpage_end_io;
62 guard_bio_eod(rw, bio);
63 submit_bio(rw, bio);
64 return NULL;
65}
66
67static struct bio *
68mpage_alloc(struct block_device *bdev,
69 sector_t first_sector, int nr_vecs,
70 gfp_t gfp_flags)
71{
72 struct bio *bio;
73
74 bio = bio_alloc(gfp_flags, nr_vecs);
75
76 if (bio == NULL && (current->flags & PF_MEMALLOC)) {
77 while (!bio && (nr_vecs /= 2))
78 bio = bio_alloc(gfp_flags, nr_vecs);
79 }
80
81 if (bio) {
82 bio->bi_bdev = bdev;
83 bio->bi_iter.bi_sector = first_sector;
84 }
85 return bio;
86}
87
88/*
89 * support function for mpage_readpages. 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 readpage 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 */
98static void
99map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
100{
101 struct inode *inode = page->mapping->host;
102 struct buffer_head *page_bh, *head;
103 int block = 0;
104
105 if (!page_has_buffers(page)) {
106 /*
107 * don't make any buffers if there is only one buffer on
108 * the page and the page just needs to be set up to date
109 */
110 if (inode->i_blkbits == PAGE_SHIFT &&
111 buffer_uptodate(bh)) {
112 SetPageUptodate(page);
113 return;
114 }
115 create_empty_buffers(page, 1 << inode->i_blkbits, 0);
116 }
117 head = page_buffers(page);
118 page_bh = head;
119 do {
120 if (block == page_block) {
121 page_bh->b_state = bh->b_state;
122 page_bh->b_bdev = bh->b_bdev;
123 page_bh->b_blocknr = bh->b_blocknr;
124 break;
125 }
126 page_bh = page_bh->b_this_page;
127 block++;
128 } while (page_bh != head);
129}
130
131/*
132 * This is the worker routine which does all the work of mapping the disk
133 * blocks and constructs largest possible bios, submits them for IO if the
134 * blocks are not contiguous on the disk.
135 *
136 * We pass a buffer_head back and forth and use its buffer_mapped() flag to
137 * represent the validity of its disk mapping and to decide when to do the next
138 * get_block() call.
139 */
140static struct bio *
141do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
142 sector_t *last_block_in_bio, struct buffer_head *map_bh,
143 unsigned long *first_logical_block, get_block_t get_block,
144 gfp_t gfp)
145{
146 struct inode *inode = page->mapping->host;
147 const unsigned blkbits = inode->i_blkbits;
148 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
149 const unsigned blocksize = 1 << blkbits;
150 sector_t block_in_file;
151 sector_t last_block;
152 sector_t last_block_in_file;
153 sector_t blocks[MAX_BUF_PER_PAGE];
154 unsigned page_block;
155 unsigned first_hole = blocks_per_page;
156 struct block_device *bdev = NULL;
157 int length;
158 int fully_mapped = 1;
159 unsigned nblocks;
160 unsigned relative_block;
161
162 if (page_has_buffers(page))
163 goto confused;
164
165 block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
166 last_block = block_in_file + nr_pages * blocks_per_page;
167 last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
168 if (last_block > last_block_in_file)
169 last_block = last_block_in_file;
170 page_block = 0;
171
172 /*
173 * Map blocks using the result from the previous get_blocks call first.
174 */
175 nblocks = map_bh->b_size >> blkbits;
176 if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
177 block_in_file < (*first_logical_block + nblocks)) {
178 unsigned map_offset = block_in_file - *first_logical_block;
179 unsigned last = nblocks - map_offset;
180
181 for (relative_block = 0; ; relative_block++) {
182 if (relative_block == last) {
183 clear_buffer_mapped(map_bh);
184 break;
185 }
186 if (page_block == blocks_per_page)
187 break;
188 blocks[page_block] = map_bh->b_blocknr + map_offset +
189 relative_block;
190 page_block++;
191 block_in_file++;
192 }
193 bdev = map_bh->b_bdev;
194 }
195
196 /*
197 * Then do more get_blocks calls until we are done with this page.
198 */
199 map_bh->b_page = page;
200 while (page_block < blocks_per_page) {
201 map_bh->b_state = 0;
202 map_bh->b_size = 0;
203
204 if (block_in_file < last_block) {
205 map_bh->b_size = (last_block-block_in_file) << blkbits;
206 if (get_block(inode, block_in_file, map_bh, 0))
207 goto confused;
208 *first_logical_block = block_in_file;
209 }
210
211 if (!buffer_mapped(map_bh)) {
212 fully_mapped = 0;
213 if (first_hole == blocks_per_page)
214 first_hole = page_block;
215 page_block++;
216 block_in_file++;
217 continue;
218 }
219
220 /* some filesystems will copy data into the page during
221 * the get_block call, in which case we don't want to
222 * read it again. map_buffer_to_page copies the data
223 * we just collected from get_block into the page's buffers
224 * so readpage doesn't have to repeat the get_block call
225 */
226 if (buffer_uptodate(map_bh)) {
227 map_buffer_to_page(page, map_bh, page_block);
228 goto confused;
229 }
230
231 if (first_hole != blocks_per_page)
232 goto confused; /* hole -> non-hole */
233
234 /* Contiguous blocks? */
235 if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
236 goto confused;
237 nblocks = map_bh->b_size >> blkbits;
238 for (relative_block = 0; ; relative_block++) {
239 if (relative_block == nblocks) {
240 clear_buffer_mapped(map_bh);
241 break;
242 } else if (page_block == blocks_per_page)
243 break;
244 blocks[page_block] = map_bh->b_blocknr+relative_block;
245 page_block++;
246 block_in_file++;
247 }
248 bdev = map_bh->b_bdev;
249 }
250
251 if (first_hole != blocks_per_page) {
252 zero_user_segment(page, first_hole << blkbits, PAGE_SIZE);
253 if (first_hole == 0) {
254 SetPageUptodate(page);
255 unlock_page(page);
256 goto out;
257 }
258 } else if (fully_mapped) {
259 SetPageMappedToDisk(page);
260 }
261
262 if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) &&
263 cleancache_get_page(page) == 0) {
264 SetPageUptodate(page);
265 goto confused;
266 }
267
268 /*
269 * This page will go to BIO. Do we need to send this BIO off first?
270 */
271 if (bio && (*last_block_in_bio != blocks[0] - 1))
272 bio = mpage_bio_submit(READ, bio);
273
274alloc_new:
275 if (bio == NULL) {
276 if (first_hole == blocks_per_page) {
277 if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
278 page))
279 goto out;
280 }
281 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
282 min_t(int, nr_pages, BIO_MAX_PAGES), gfp);
283 if (bio == NULL)
284 goto confused;
285 }
286
287 length = first_hole << blkbits;
288 if (bio_add_page(bio, page, length, 0) < length) {
289 bio = mpage_bio_submit(READ, bio);
290 goto alloc_new;
291 }
292
293 relative_block = block_in_file - *first_logical_block;
294 nblocks = map_bh->b_size >> blkbits;
295 if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
296 (first_hole != blocks_per_page))
297 bio = mpage_bio_submit(READ, bio);
298 else
299 *last_block_in_bio = blocks[blocks_per_page - 1];
300out:
301 return bio;
302
303confused:
304 if (bio)
305 bio = mpage_bio_submit(READ, bio);
306 if (!PageUptodate(page))
307 block_read_full_page(page, get_block);
308 else
309 unlock_page(page);
310 goto out;
311}
312
313/**
314 * mpage_readpages - populate an address space with some pages & start reads against them
315 * @mapping: the address_space
316 * @pages: The address of a list_head which contains the target pages. These
317 * pages have their ->index populated and are otherwise uninitialised.
318 * The page at @pages->prev has the lowest file offset, and reads should be
319 * issued in @pages->prev to @pages->next order.
320 * @nr_pages: The number of pages at *@pages
321 * @get_block: The filesystem's block mapper function.
322 *
323 * This function walks the pages and the blocks within each page, building and
324 * emitting large BIOs.
325 *
326 * If anything unusual happens, such as:
327 *
328 * - encountering a page which has buffers
329 * - encountering a page which has a non-hole after a hole
330 * - encountering a page with non-contiguous blocks
331 *
332 * then this code just gives up and calls the buffer_head-based read function.
333 * It does handle a page which has holes at the end - that is a common case:
334 * the end-of-file on blocksize < PAGE_SIZE setups.
335 *
336 * BH_Boundary explanation:
337 *
338 * There is a problem. The mpage read code assembles several pages, gets all
339 * their disk mappings, and then submits them all. That's fine, but obtaining
340 * the disk mappings may require I/O. Reads of indirect blocks, for example.
341 *
342 * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
343 * submitted in the following order:
344 * 12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
345 *
346 * because the indirect block has to be read to get the mappings of blocks
347 * 13,14,15,16. Obviously, this impacts performance.
348 *
349 * So what we do it to allow the filesystem's get_block() function to set
350 * BH_Boundary when it maps block 11. BH_Boundary says: mapping of the block
351 * after this one will require I/O against a block which is probably close to
352 * this one. So you should push what I/O you have currently accumulated.
353 *
354 * This all causes the disk requests to be issued in the correct order.
355 */
356int
357mpage_readpages(struct address_space *mapping, struct list_head *pages,
358 unsigned nr_pages, get_block_t get_block)
359{
360 struct bio *bio = NULL;
361 unsigned page_idx;
362 sector_t last_block_in_bio = 0;
363 struct buffer_head map_bh;
364 unsigned long first_logical_block = 0;
365 gfp_t gfp = mapping_gfp_constraint(mapping, GFP_KERNEL);
366
367 map_bh.b_state = 0;
368 map_bh.b_size = 0;
369 for (page_idx = 0; page_idx < nr_pages; page_idx++) {
370 struct page *page = lru_to_page(pages);
371
372 prefetchw(&page->flags);
373 list_del(&page->lru);
374 if (!add_to_page_cache_lru(page, mapping,
375 page->index,
376 gfp)) {
377 bio = do_mpage_readpage(bio, page,
378 nr_pages - page_idx,
379 &last_block_in_bio, &map_bh,
380 &first_logical_block,
381 get_block, gfp);
382 }
383 put_page(page);
384 }
385 BUG_ON(!list_empty(pages));
386 if (bio)
387 mpage_bio_submit(READ, bio);
388 return 0;
389}
390EXPORT_SYMBOL(mpage_readpages);
391
392/*
393 * This isn't called much at all
394 */
395int mpage_readpage(struct page *page, get_block_t get_block)
396{
397 struct bio *bio = NULL;
398 sector_t last_block_in_bio = 0;
399 struct buffer_head map_bh;
400 unsigned long first_logical_block = 0;
401 gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
402
403 map_bh.b_state = 0;
404 map_bh.b_size = 0;
405 bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
406 &map_bh, &first_logical_block, get_block, gfp);
407 if (bio)
408 mpage_bio_submit(READ, bio);
409 return 0;
410}
411EXPORT_SYMBOL(mpage_readpage);
412
413/*
414 * Writing is not so simple.
415 *
416 * If the page has buffers then they will be used for obtaining the disk
417 * mapping. We only support pages which are fully mapped-and-dirty, with a
418 * special case for pages which are unmapped at the end: end-of-file.
419 *
420 * If the page has no buffers (preferred) then the page is mapped here.
421 *
422 * If all blocks are found to be contiguous then the page can go into the
423 * BIO. Otherwise fall back to the mapping's writepage().
424 *
425 * FIXME: This code wants an estimate of how many pages are still to be
426 * written, so it can intelligently allocate a suitably-sized BIO. For now,
427 * just allocate full-size (16-page) BIOs.
428 */
429
430struct mpage_data {
431 struct bio *bio;
432 sector_t last_block_in_bio;
433 get_block_t *get_block;
434 unsigned use_writepage;
435};
436
437/*
438 * We have our BIO, so we can now mark the buffers clean. Make
439 * sure to only clean buffers which we know we'll be writing.
440 */
441static void clean_buffers(struct page *page, unsigned first_unmapped)
442{
443 unsigned buffer_counter = 0;
444 struct buffer_head *bh, *head;
445 if (!page_has_buffers(page))
446 return;
447 head = page_buffers(page);
448 bh = head;
449
450 do {
451 if (buffer_counter++ == first_unmapped)
452 break;
453 clear_buffer_dirty(bh);
454 bh = bh->b_this_page;
455 } while (bh != head);
456
457 /*
458 * we cannot drop the bh if the page is not uptodate or a concurrent
459 * readpage would fail to serialize with the bh and it would read from
460 * disk before we reach the platter.
461 */
462 if (buffer_heads_over_limit && PageUptodate(page))
463 try_to_free_buffers(page);
464}
465
466static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
467 void *data)
468{
469 struct mpage_data *mpd = data;
470 struct bio *bio = mpd->bio;
471 struct address_space *mapping = page->mapping;
472 struct inode *inode = page->mapping->host;
473 const unsigned blkbits = inode->i_blkbits;
474 unsigned long end_index;
475 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
476 sector_t last_block;
477 sector_t block_in_file;
478 sector_t blocks[MAX_BUF_PER_PAGE];
479 unsigned page_block;
480 unsigned first_unmapped = blocks_per_page;
481 struct block_device *bdev = NULL;
482 int boundary = 0;
483 sector_t boundary_block = 0;
484 struct block_device *boundary_bdev = NULL;
485 int length;
486 struct buffer_head map_bh;
487 loff_t i_size = i_size_read(inode);
488 int ret = 0;
489 int wr = (wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE);
490
491 if (page_has_buffers(page)) {
492 struct buffer_head *head = page_buffers(page);
493 struct buffer_head *bh = head;
494
495 /* If they're all mapped and dirty, do it */
496 page_block = 0;
497 do {
498 BUG_ON(buffer_locked(bh));
499 if (!buffer_mapped(bh)) {
500 /*
501 * unmapped dirty buffers are created by
502 * __set_page_dirty_buffers -> mmapped data
503 */
504 if (buffer_dirty(bh))
505 goto confused;
506 if (first_unmapped == blocks_per_page)
507 first_unmapped = page_block;
508 continue;
509 }
510
511 if (first_unmapped != blocks_per_page)
512 goto confused; /* hole -> non-hole */
513
514 if (!buffer_dirty(bh) || !buffer_uptodate(bh))
515 goto confused;
516 if (page_block) {
517 if (bh->b_blocknr != blocks[page_block-1] + 1)
518 goto confused;
519 }
520 blocks[page_block++] = bh->b_blocknr;
521 boundary = buffer_boundary(bh);
522 if (boundary) {
523 boundary_block = bh->b_blocknr;
524 boundary_bdev = bh->b_bdev;
525 }
526 bdev = bh->b_bdev;
527 } while ((bh = bh->b_this_page) != head);
528
529 if (first_unmapped)
530 goto page_is_mapped;
531
532 /*
533 * Page has buffers, but they are all unmapped. The page was
534 * created by pagein or read over a hole which was handled by
535 * block_read_full_page(). If this address_space is also
536 * using mpage_readpages then this can rarely happen.
537 */
538 goto confused;
539 }
540
541 /*
542 * The page has no buffers: map it to disk
543 */
544 BUG_ON(!PageUptodate(page));
545 block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
546 last_block = (i_size - 1) >> blkbits;
547 map_bh.b_page = page;
548 for (page_block = 0; page_block < blocks_per_page; ) {
549
550 map_bh.b_state = 0;
551 map_bh.b_size = 1 << blkbits;
552 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
553 goto confused;
554 if (buffer_new(&map_bh))
555 unmap_underlying_metadata(map_bh.b_bdev,
556 map_bh.b_blocknr);
557 if (buffer_boundary(&map_bh)) {
558 boundary_block = map_bh.b_blocknr;
559 boundary_bdev = map_bh.b_bdev;
560 }
561 if (page_block) {
562 if (map_bh.b_blocknr != blocks[page_block-1] + 1)
563 goto confused;
564 }
565 blocks[page_block++] = map_bh.b_blocknr;
566 boundary = buffer_boundary(&map_bh);
567 bdev = map_bh.b_bdev;
568 if (block_in_file == last_block)
569 break;
570 block_in_file++;
571 }
572 BUG_ON(page_block == 0);
573
574 first_unmapped = page_block;
575
576page_is_mapped:
577 end_index = i_size >> PAGE_SHIFT;
578 if (page->index >= end_index) {
579 /*
580 * The page straddles i_size. It must be zeroed out on each
581 * and every writepage invocation because it may be mmapped.
582 * "A file is mapped in multiples of the page size. For a file
583 * that is not a multiple of the page size, the remaining memory
584 * is zeroed when mapped, and writes to that region are not
585 * written out to the file."
586 */
587 unsigned offset = i_size & (PAGE_SIZE - 1);
588
589 if (page->index > end_index || !offset)
590 goto confused;
591 zero_user_segment(page, offset, PAGE_SIZE);
592 }
593
594 /*
595 * This page will go to BIO. Do we need to send this BIO off first?
596 */
597 if (bio && mpd->last_block_in_bio != blocks[0] - 1)
598 bio = mpage_bio_submit(wr, bio);
599
600alloc_new:
601 if (bio == NULL) {
602 if (first_unmapped == blocks_per_page) {
603 if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
604 page, wbc)) {
605 clean_buffers(page, first_unmapped);
606 goto out;
607 }
608 }
609 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
610 BIO_MAX_PAGES, GFP_NOFS|__GFP_HIGH);
611 if (bio == NULL)
612 goto confused;
613
614 wbc_init_bio(wbc, bio);
615 }
616
617 /*
618 * Must try to add the page before marking the buffer clean or
619 * the confused fail path above (OOM) will be very confused when
620 * it finds all bh marked clean (i.e. it will not write anything)
621 */
622 wbc_account_io(wbc, page, PAGE_SIZE);
623 length = first_unmapped << blkbits;
624 if (bio_add_page(bio, page, length, 0) < length) {
625 bio = mpage_bio_submit(wr, bio);
626 goto alloc_new;
627 }
628
629 clean_buffers(page, first_unmapped);
630
631 BUG_ON(PageWriteback(page));
632 set_page_writeback(page);
633 unlock_page(page);
634 if (boundary || (first_unmapped != blocks_per_page)) {
635 bio = mpage_bio_submit(wr, bio);
636 if (boundary_block) {
637 write_boundary_block(boundary_bdev,
638 boundary_block, 1 << blkbits);
639 }
640 } else {
641 mpd->last_block_in_bio = blocks[blocks_per_page - 1];
642 }
643 goto out;
644
645confused:
646 if (bio)
647 bio = mpage_bio_submit(wr, bio);
648
649 if (mpd->use_writepage) {
650 ret = mapping->a_ops->writepage(page, wbc);
651 } else {
652 ret = -EAGAIN;
653 goto out;
654 }
655 /*
656 * The caller has a ref on the inode, so *mapping is stable
657 */
658 mapping_set_error(mapping, ret);
659out:
660 mpd->bio = bio;
661 return ret;
662}
663
664/**
665 * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
666 * @mapping: address space structure to write
667 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
668 * @get_block: the filesystem's block mapper function.
669 * If this is NULL then use a_ops->writepage. Otherwise, go
670 * direct-to-BIO.
671 *
672 * This is a library function, which implements the writepages()
673 * address_space_operation.
674 *
675 * If a page is already under I/O, generic_writepages() skips it, even
676 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
677 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
678 * and msync() need to guarantee that all the data which was dirty at the time
679 * the call was made get new I/O started against them. If wbc->sync_mode is
680 * WB_SYNC_ALL then we were called for data integrity and we must wait for
681 * existing IO to complete.
682 */
683int
684mpage_writepages(struct address_space *mapping,
685 struct writeback_control *wbc, get_block_t get_block)
686{
687 struct blk_plug plug;
688 int ret;
689
690 blk_start_plug(&plug);
691
692 if (!get_block)
693 ret = generic_writepages(mapping, wbc);
694 else {
695 struct mpage_data mpd = {
696 .bio = NULL,
697 .last_block_in_bio = 0,
698 .get_block = get_block,
699 .use_writepage = 1,
700 };
701
702 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
703 if (mpd.bio) {
704 int wr = (wbc->sync_mode == WB_SYNC_ALL ?
705 WRITE_SYNC : WRITE);
706 mpage_bio_submit(wr, mpd.bio);
707 }
708 }
709 blk_finish_plug(&plug);
710 return ret;
711}
712EXPORT_SYMBOL(mpage_writepages);
713
714int mpage_writepage(struct page *page, get_block_t get_block,
715 struct writeback_control *wbc)
716{
717 struct mpage_data mpd = {
718 .bio = NULL,
719 .last_block_in_bio = 0,
720 .get_block = get_block,
721 .use_writepage = 0,
722 };
723 int ret = __mpage_writepage(page, wbc, &mpd);
724 if (mpd.bio) {
725 int wr = (wbc->sync_mode == WB_SYNC_ALL ?
726 WRITE_SYNC : WRITE);
727 mpage_bio_submit(wr, mpd.bio);
728 }
729 return ret;
730}
731EXPORT_SYMBOL(mpage_writepage);
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 */
46static 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 folio_end_read(fi.folio, err == 0);
53
54 bio_put(bio);
55}
56
57static void mpage_write_end_io(struct bio *bio)
58{
59 struct folio_iter fi;
60 int err = blk_status_to_errno(bio->bi_status);
61
62 bio_for_each_folio_all(fi, bio) {
63 if (err)
64 mapping_set_error(fi.folio->mapping, err);
65 folio_end_writeback(fi.folio);
66 }
67
68 bio_put(bio);
69}
70
71static struct bio *mpage_bio_submit_read(struct bio *bio)
72{
73 bio->bi_end_io = mpage_read_end_io;
74 guard_bio_eod(bio);
75 submit_bio(bio);
76 return NULL;
77}
78
79static struct bio *mpage_bio_submit_write(struct bio *bio)
80{
81 bio->bi_end_io = mpage_write_end_io;
82 guard_bio_eod(bio);
83 submit_bio(bio);
84 return NULL;
85}
86
87/*
88 * support function for mpage_readahead. The fs supplied get_block might
89 * return an up to date buffer. This is used to map that buffer into
90 * the page, which allows read_folio to avoid triggering a duplicate call
91 * to get_block.
92 *
93 * The idea is to avoid adding buffers to pages that don't already have
94 * them. So when the buffer is up to date and the page size == block size,
95 * this marks the page up to date instead of adding new buffers.
96 */
97static void map_buffer_to_folio(struct folio *folio, struct buffer_head *bh,
98 int page_block)
99{
100 struct inode *inode = folio->mapping->host;
101 struct buffer_head *page_bh, *head;
102 int block = 0;
103
104 head = folio_buffers(folio);
105 if (!head) {
106 /*
107 * don't make any buffers if there is only one buffer on
108 * the folio and the folio just needs to be set up to date
109 */
110 if (inode->i_blkbits == PAGE_SHIFT &&
111 buffer_uptodate(bh)) {
112 folio_mark_uptodate(folio);
113 return;
114 }
115 head = create_empty_buffers(folio, i_blocksize(inode), 0);
116 }
117
118 page_bh = head;
119 do {
120 if (block == page_block) {
121 page_bh->b_state = bh->b_state;
122 page_bh->b_bdev = bh->b_bdev;
123 page_bh->b_blocknr = bh->b_blocknr;
124 break;
125 }
126 page_bh = page_bh->b_this_page;
127 block++;
128 } while (page_bh != head);
129}
130
131struct mpage_readpage_args {
132 struct bio *bio;
133 struct folio *folio;
134 unsigned int nr_pages;
135 bool is_readahead;
136 sector_t last_block_in_bio;
137 struct buffer_head map_bh;
138 unsigned long first_logical_block;
139 get_block_t *get_block;
140};
141
142/*
143 * This is the worker routine which does all the work of mapping the disk
144 * blocks and constructs largest possible bios, submits them for IO if the
145 * blocks are not contiguous on the disk.
146 *
147 * We pass a buffer_head back and forth and use its buffer_mapped() flag to
148 * represent the validity of its disk mapping and to decide when to do the next
149 * get_block() call.
150 */
151static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
152{
153 struct folio *folio = args->folio;
154 struct inode *inode = folio->mapping->host;
155 const unsigned blkbits = inode->i_blkbits;
156 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
157 const unsigned blocksize = 1 << blkbits;
158 struct buffer_head *map_bh = &args->map_bh;
159 sector_t block_in_file;
160 sector_t last_block;
161 sector_t last_block_in_file;
162 sector_t first_block;
163 unsigned page_block;
164 unsigned first_hole = blocks_per_page;
165 struct block_device *bdev = NULL;
166 int length;
167 int fully_mapped = 1;
168 blk_opf_t opf = REQ_OP_READ;
169 unsigned nblocks;
170 unsigned relative_block;
171 gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
172
173 /* MAX_BUF_PER_PAGE, for example */
174 VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
175
176 if (args->is_readahead) {
177 opf |= REQ_RAHEAD;
178 gfp |= __GFP_NORETRY | __GFP_NOWARN;
179 }
180
181 if (folio_buffers(folio))
182 goto confused;
183
184 block_in_file = (sector_t)folio->index << (PAGE_SHIFT - blkbits);
185 last_block = block_in_file + args->nr_pages * blocks_per_page;
186 last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
187 if (last_block > last_block_in_file)
188 last_block = last_block_in_file;
189 page_block = 0;
190
191 /*
192 * Map blocks using the result from the previous get_blocks call first.
193 */
194 nblocks = map_bh->b_size >> blkbits;
195 if (buffer_mapped(map_bh) &&
196 block_in_file > args->first_logical_block &&
197 block_in_file < (args->first_logical_block + nblocks)) {
198 unsigned map_offset = block_in_file - args->first_logical_block;
199 unsigned last = nblocks - map_offset;
200
201 first_block = map_bh->b_blocknr + map_offset;
202 for (relative_block = 0; ; relative_block++) {
203 if (relative_block == last) {
204 clear_buffer_mapped(map_bh);
205 break;
206 }
207 if (page_block == blocks_per_page)
208 break;
209 page_block++;
210 block_in_file++;
211 }
212 bdev = map_bh->b_bdev;
213 }
214
215 /*
216 * Then do more get_blocks calls until we are done with this folio.
217 */
218 map_bh->b_folio = folio;
219 while (page_block < blocks_per_page) {
220 map_bh->b_state = 0;
221 map_bh->b_size = 0;
222
223 if (block_in_file < last_block) {
224 map_bh->b_size = (last_block-block_in_file) << blkbits;
225 if (args->get_block(inode, block_in_file, map_bh, 0))
226 goto confused;
227 args->first_logical_block = block_in_file;
228 }
229
230 if (!buffer_mapped(map_bh)) {
231 fully_mapped = 0;
232 if (first_hole == blocks_per_page)
233 first_hole = page_block;
234 page_block++;
235 block_in_file++;
236 continue;
237 }
238
239 /* some filesystems will copy data into the page during
240 * the get_block call, in which case we don't want to
241 * read it again. map_buffer_to_folio copies the data
242 * we just collected from get_block into the folio's buffers
243 * so read_folio doesn't have to repeat the get_block call
244 */
245 if (buffer_uptodate(map_bh)) {
246 map_buffer_to_folio(folio, map_bh, page_block);
247 goto confused;
248 }
249
250 if (first_hole != blocks_per_page)
251 goto confused; /* hole -> non-hole */
252
253 /* Contiguous blocks? */
254 if (!page_block)
255 first_block = map_bh->b_blocknr;
256 else if (first_block + page_block != map_bh->b_blocknr)
257 goto confused;
258 nblocks = map_bh->b_size >> blkbits;
259 for (relative_block = 0; ; relative_block++) {
260 if (relative_block == nblocks) {
261 clear_buffer_mapped(map_bh);
262 break;
263 } else if (page_block == blocks_per_page)
264 break;
265 page_block++;
266 block_in_file++;
267 }
268 bdev = map_bh->b_bdev;
269 }
270
271 if (first_hole != blocks_per_page) {
272 folio_zero_segment(folio, first_hole << blkbits, PAGE_SIZE);
273 if (first_hole == 0) {
274 folio_mark_uptodate(folio);
275 folio_unlock(folio);
276 goto out;
277 }
278 } else if (fully_mapped) {
279 folio_set_mappedtodisk(folio);
280 }
281
282 /*
283 * This folio will go to BIO. Do we need to send this BIO off first?
284 */
285 if (args->bio && (args->last_block_in_bio != first_block - 1))
286 args->bio = mpage_bio_submit_read(args->bio);
287
288alloc_new:
289 if (args->bio == NULL) {
290 args->bio = bio_alloc(bdev, bio_max_segs(args->nr_pages), opf,
291 gfp);
292 if (args->bio == NULL)
293 goto confused;
294 args->bio->bi_iter.bi_sector = first_block << (blkbits - 9);
295 }
296
297 length = first_hole << blkbits;
298 if (!bio_add_folio(args->bio, folio, length, 0)) {
299 args->bio = mpage_bio_submit_read(args->bio);
300 goto alloc_new;
301 }
302
303 relative_block = block_in_file - args->first_logical_block;
304 nblocks = map_bh->b_size >> blkbits;
305 if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
306 (first_hole != blocks_per_page))
307 args->bio = mpage_bio_submit_read(args->bio);
308 else
309 args->last_block_in_bio = first_block + blocks_per_page - 1;
310out:
311 return args->bio;
312
313confused:
314 if (args->bio)
315 args->bio = mpage_bio_submit_read(args->bio);
316 if (!folio_test_uptodate(folio))
317 block_read_full_folio(folio, args->get_block);
318 else
319 folio_unlock(folio);
320 goto out;
321}
322
323/**
324 * mpage_readahead - start reads against pages
325 * @rac: Describes which pages to read.
326 * @get_block: The filesystem's block mapper function.
327 *
328 * This function walks the pages and the blocks within each page, building and
329 * emitting large BIOs.
330 *
331 * If anything unusual happens, such as:
332 *
333 * - encountering a page which has buffers
334 * - encountering a page which has a non-hole after a hole
335 * - encountering a page with non-contiguous blocks
336 *
337 * then this code just gives up and calls the buffer_head-based read function.
338 * It does handle a page which has holes at the end - that is a common case:
339 * the end-of-file on blocksize < PAGE_SIZE setups.
340 *
341 * BH_Boundary explanation:
342 *
343 * There is a problem. The mpage read code assembles several pages, gets all
344 * their disk mappings, and then submits them all. That's fine, but obtaining
345 * the disk mappings may require I/O. Reads of indirect blocks, for example.
346 *
347 * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
348 * submitted in the following order:
349 *
350 * 12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
351 *
352 * because the indirect block has to be read to get the mappings of blocks
353 * 13,14,15,16. Obviously, this impacts performance.
354 *
355 * So what we do it to allow the filesystem's get_block() function to set
356 * BH_Boundary when it maps block 11. BH_Boundary says: mapping of the block
357 * after this one will require I/O against a block which is probably close to
358 * this one. So you should push what I/O you have currently accumulated.
359 *
360 * This all causes the disk requests to be issued in the correct order.
361 */
362void mpage_readahead(struct readahead_control *rac, get_block_t get_block)
363{
364 struct folio *folio;
365 struct mpage_readpage_args args = {
366 .get_block = get_block,
367 .is_readahead = true,
368 };
369
370 while ((folio = readahead_folio(rac))) {
371 prefetchw(&folio->flags);
372 args.folio = folio;
373 args.nr_pages = readahead_count(rac);
374 args.bio = do_mpage_readpage(&args);
375 }
376 if (args.bio)
377 mpage_bio_submit_read(args.bio);
378}
379EXPORT_SYMBOL(mpage_readahead);
380
381/*
382 * This isn't called much at all
383 */
384int mpage_read_folio(struct folio *folio, get_block_t get_block)
385{
386 struct mpage_readpage_args args = {
387 .folio = folio,
388 .nr_pages = 1,
389 .get_block = get_block,
390 };
391
392 args.bio = do_mpage_readpage(&args);
393 if (args.bio)
394 mpage_bio_submit_read(args.bio);
395 return 0;
396}
397EXPORT_SYMBOL(mpage_read_folio);
398
399/*
400 * Writing is not so simple.
401 *
402 * If the page has buffers then they will be used for obtaining the disk
403 * mapping. We only support pages which are fully mapped-and-dirty, with a
404 * special case for pages which are unmapped at the end: end-of-file.
405 *
406 * If the page has no buffers (preferred) then the page is mapped here.
407 *
408 * If all blocks are found to be contiguous then the page can go into the
409 * BIO. Otherwise fall back to the mapping's writepage().
410 *
411 * FIXME: This code wants an estimate of how many pages are still to be
412 * written, so it can intelligently allocate a suitably-sized BIO. For now,
413 * just allocate full-size (16-page) BIOs.
414 */
415
416struct mpage_data {
417 struct bio *bio;
418 sector_t last_block_in_bio;
419 get_block_t *get_block;
420};
421
422/*
423 * We have our BIO, so we can now mark the buffers clean. Make
424 * sure to only clean buffers which we know we'll be writing.
425 */
426static void clean_buffers(struct folio *folio, unsigned first_unmapped)
427{
428 unsigned buffer_counter = 0;
429 struct buffer_head *bh, *head = folio_buffers(folio);
430
431 if (!head)
432 return;
433 bh = head;
434
435 do {
436 if (buffer_counter++ == first_unmapped)
437 break;
438 clear_buffer_dirty(bh);
439 bh = bh->b_this_page;
440 } while (bh != head);
441
442 /*
443 * we cannot drop the bh if the page is not uptodate or a concurrent
444 * read_folio would fail to serialize with the bh and it would read from
445 * disk before we reach the platter.
446 */
447 if (buffer_heads_over_limit && folio_test_uptodate(folio))
448 try_to_free_buffers(folio);
449}
450
451static int __mpage_writepage(struct folio *folio, struct writeback_control *wbc,
452 void *data)
453{
454 struct mpage_data *mpd = data;
455 struct bio *bio = mpd->bio;
456 struct address_space *mapping = folio->mapping;
457 struct inode *inode = mapping->host;
458 const unsigned blkbits = inode->i_blkbits;
459 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
460 sector_t last_block;
461 sector_t block_in_file;
462 sector_t first_block;
463 unsigned page_block;
464 unsigned first_unmapped = blocks_per_page;
465 struct block_device *bdev = NULL;
466 int boundary = 0;
467 sector_t boundary_block = 0;
468 struct block_device *boundary_bdev = NULL;
469 size_t length;
470 struct buffer_head map_bh;
471 loff_t i_size = i_size_read(inode);
472 int ret = 0;
473 struct buffer_head *head = folio_buffers(folio);
474
475 if (head) {
476 struct buffer_head *bh = head;
477
478 /* If they're all mapped and dirty, do it */
479 page_block = 0;
480 do {
481 BUG_ON(buffer_locked(bh));
482 if (!buffer_mapped(bh)) {
483 /*
484 * unmapped dirty buffers are created by
485 * block_dirty_folio -> mmapped data
486 */
487 if (buffer_dirty(bh))
488 goto confused;
489 if (first_unmapped == blocks_per_page)
490 first_unmapped = page_block;
491 continue;
492 }
493
494 if (first_unmapped != blocks_per_page)
495 goto confused; /* hole -> non-hole */
496
497 if (!buffer_dirty(bh) || !buffer_uptodate(bh))
498 goto confused;
499 if (page_block) {
500 if (bh->b_blocknr != first_block + page_block)
501 goto confused;
502 } else {
503 first_block = bh->b_blocknr;
504 }
505 page_block++;
506 boundary = buffer_boundary(bh);
507 if (boundary) {
508 boundary_block = bh->b_blocknr;
509 boundary_bdev = bh->b_bdev;
510 }
511 bdev = bh->b_bdev;
512 } while ((bh = bh->b_this_page) != head);
513
514 if (first_unmapped)
515 goto page_is_mapped;
516
517 /*
518 * Page has buffers, but they are all unmapped. The page was
519 * created by pagein or read over a hole which was handled by
520 * block_read_full_folio(). If this address_space is also
521 * using mpage_readahead then this can rarely happen.
522 */
523 goto confused;
524 }
525
526 /*
527 * The page has no buffers: map it to disk
528 */
529 BUG_ON(!folio_test_uptodate(folio));
530 block_in_file = (sector_t)folio->index << (PAGE_SHIFT - blkbits);
531 /*
532 * Whole page beyond EOF? Skip allocating blocks to avoid leaking
533 * space.
534 */
535 if (block_in_file >= (i_size + (1 << blkbits) - 1) >> blkbits)
536 goto page_is_mapped;
537 last_block = (i_size - 1) >> blkbits;
538 map_bh.b_folio = folio;
539 for (page_block = 0; page_block < blocks_per_page; ) {
540
541 map_bh.b_state = 0;
542 map_bh.b_size = 1 << blkbits;
543 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
544 goto confused;
545 if (!buffer_mapped(&map_bh))
546 goto confused;
547 if (buffer_new(&map_bh))
548 clean_bdev_bh_alias(&map_bh);
549 if (buffer_boundary(&map_bh)) {
550 boundary_block = map_bh.b_blocknr;
551 boundary_bdev = map_bh.b_bdev;
552 }
553 if (page_block) {
554 if (map_bh.b_blocknr != first_block + page_block)
555 goto confused;
556 } else {
557 first_block = map_bh.b_blocknr;
558 }
559 page_block++;
560 boundary = buffer_boundary(&map_bh);
561 bdev = map_bh.b_bdev;
562 if (block_in_file == last_block)
563 break;
564 block_in_file++;
565 }
566 BUG_ON(page_block == 0);
567
568 first_unmapped = page_block;
569
570page_is_mapped:
571 /* Don't bother writing beyond EOF, truncate will discard the folio */
572 if (folio_pos(folio) >= i_size)
573 goto confused;
574 length = folio_size(folio);
575 if (folio_pos(folio) + length > i_size) {
576 /*
577 * The page straddles i_size. It must be zeroed out on each
578 * and every writepage invocation because it may be mmapped.
579 * "A file is mapped in multiples of the page size. For a file
580 * that is not a multiple of the page size, the remaining memory
581 * is zeroed when mapped, and writes to that region are not
582 * written out to the file."
583 */
584 length = i_size - folio_pos(folio);
585 folio_zero_segment(folio, length, folio_size(folio));
586 }
587
588 /*
589 * This page will go to BIO. Do we need to send this BIO off first?
590 */
591 if (bio && mpd->last_block_in_bio != first_block - 1)
592 bio = mpage_bio_submit_write(bio);
593
594alloc_new:
595 if (bio == NULL) {
596 bio = bio_alloc(bdev, BIO_MAX_VECS,
597 REQ_OP_WRITE | wbc_to_write_flags(wbc),
598 GFP_NOFS);
599 bio->bi_iter.bi_sector = first_block << (blkbits - 9);
600 wbc_init_bio(wbc, bio);
601 bio->bi_write_hint = inode->i_write_hint;
602 }
603
604 /*
605 * Must try to add the page before marking the buffer clean or
606 * the confused fail path above (OOM) will be very confused when
607 * it finds all bh marked clean (i.e. it will not write anything)
608 */
609 wbc_account_cgroup_owner(wbc, folio, folio_size(folio));
610 length = first_unmapped << blkbits;
611 if (!bio_add_folio(bio, folio, length, 0)) {
612 bio = mpage_bio_submit_write(bio);
613 goto alloc_new;
614 }
615
616 clean_buffers(folio, first_unmapped);
617
618 BUG_ON(folio_test_writeback(folio));
619 folio_start_writeback(folio);
620 folio_unlock(folio);
621 if (boundary || (first_unmapped != blocks_per_page)) {
622 bio = mpage_bio_submit_write(bio);
623 if (boundary_block) {
624 write_boundary_block(boundary_bdev,
625 boundary_block, 1 << blkbits);
626 }
627 } else {
628 mpd->last_block_in_bio = first_block + blocks_per_page - 1;
629 }
630 goto out;
631
632confused:
633 if (bio)
634 bio = mpage_bio_submit_write(bio);
635
636 /*
637 * The caller has a ref on the inode, so *mapping is stable
638 */
639 ret = block_write_full_folio(folio, wbc, mpd->get_block);
640 mapping_set_error(mapping, ret);
641out:
642 mpd->bio = bio;
643 return ret;
644}
645
646/**
647 * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
648 * @mapping: address space structure to write
649 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
650 * @get_block: the filesystem's block mapper function.
651 *
652 * This is a library function, which implements the writepages()
653 * address_space_operation.
654 */
655int
656mpage_writepages(struct address_space *mapping,
657 struct writeback_control *wbc, get_block_t get_block)
658{
659 struct mpage_data mpd = {
660 .get_block = get_block,
661 };
662 struct blk_plug plug;
663 int ret;
664
665 blk_start_plug(&plug);
666 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
667 if (mpd.bio)
668 mpage_bio_submit_write(mpd.bio);
669 blk_finish_plug(&plug);
670 return ret;
671}
672EXPORT_SYMBOL(mpage_writepages);