1 // SPDX-License-Identifier: GPL-2.0
5 * Copyright (C) 2002, Linus Torvalds.
7 * Contains functions related to preparing and submitting BIOs which contain
8 * multiple pagecache pages.
10 * 15May2002 Andrew Morton
12 * 27Jun2002 axboe@suse.de
13 * use bio_add_page() to build bio's just the right size
16 #include <linux/kernel.h>
17 #include <linux/export.h>
19 #include <linux/kdev_t.h>
20 #include <linux/gfp.h>
21 #include <linux/bio.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>
35 * I/O completion handler for multipage BIOs.
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().
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.
46 static void mpage_end_io(struct bio *bio)
49 struct bvec_iter_all iter_all;
51 bio_for_each_segment_all(bv, bio, iter_all) {
52 struct page *page = bv->bv_page;
53 page_endio(page, bio_op(bio),
54 blk_status_to_errno(bio->bi_status));
60 static struct bio *mpage_bio_submit(struct bio *bio)
62 bio->bi_end_io = mpage_end_io;
69 * support function for mpage_readahead. The fs supplied get_block might
70 * return an up to date buffer. This is used to map that buffer into
71 * the page, which allows read_folio to avoid triggering a duplicate call
74 * The idea is to avoid adding buffers to pages that don't already have
75 * them. So when the buffer is up to date and the page size == block size,
76 * this marks the page up to date instead of adding new buffers.
78 static void map_buffer_to_folio(struct folio *folio, struct buffer_head *bh,
81 struct inode *inode = folio->mapping->host;
82 struct buffer_head *page_bh, *head;
85 head = folio_buffers(folio);
88 * don't make any buffers if there is only one buffer on
89 * the folio and the folio just needs to be set up to date
91 if (inode->i_blkbits == PAGE_SHIFT &&
92 buffer_uptodate(bh)) {
93 folio_mark_uptodate(folio);
96 create_empty_buffers(&folio->page, i_blocksize(inode), 0);
97 head = folio_buffers(folio);
102 if (block == page_block) {
103 page_bh->b_state = bh->b_state;
104 page_bh->b_bdev = bh->b_bdev;
105 page_bh->b_blocknr = bh->b_blocknr;
108 page_bh = page_bh->b_this_page;
110 } while (page_bh != head);
113 struct mpage_readpage_args {
116 unsigned int nr_pages;
118 sector_t last_block_in_bio;
119 struct buffer_head map_bh;
120 unsigned long first_logical_block;
121 get_block_t *get_block;
125 * This is the worker routine which does all the work of mapping the disk
126 * blocks and constructs largest possible bios, submits them for IO if the
127 * blocks are not contiguous on the disk.
129 * We pass a buffer_head back and forth and use its buffer_mapped() flag to
130 * represent the validity of its disk mapping and to decide when to do the next
133 static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
135 struct folio *folio = args->folio;
136 struct inode *inode = folio->mapping->host;
137 const unsigned blkbits = inode->i_blkbits;
138 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
139 const unsigned blocksize = 1 << blkbits;
140 struct buffer_head *map_bh = &args->map_bh;
141 sector_t block_in_file;
143 sector_t last_block_in_file;
144 sector_t blocks[MAX_BUF_PER_PAGE];
146 unsigned first_hole = blocks_per_page;
147 struct block_device *bdev = NULL;
149 int fully_mapped = 1;
150 int op = REQ_OP_READ;
152 unsigned relative_block;
153 gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
155 /* MAX_BUF_PER_PAGE, for example */
156 VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
158 if (args->is_readahead) {
160 gfp |= __GFP_NORETRY | __GFP_NOWARN;
163 if (folio_buffers(folio))
166 block_in_file = (sector_t)folio->index << (PAGE_SHIFT - blkbits);
167 last_block = block_in_file + args->nr_pages * blocks_per_page;
168 last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
169 if (last_block > last_block_in_file)
170 last_block = last_block_in_file;
174 * Map blocks using the result from the previous get_blocks call first.
176 nblocks = map_bh->b_size >> blkbits;
177 if (buffer_mapped(map_bh) &&
178 block_in_file > args->first_logical_block &&
179 block_in_file < (args->first_logical_block + nblocks)) {
180 unsigned map_offset = block_in_file - args->first_logical_block;
181 unsigned last = nblocks - map_offset;
183 for (relative_block = 0; ; relative_block++) {
184 if (relative_block == last) {
185 clear_buffer_mapped(map_bh);
188 if (page_block == blocks_per_page)
190 blocks[page_block] = map_bh->b_blocknr + map_offset +
195 bdev = map_bh->b_bdev;
199 * Then do more get_blocks calls until we are done with this folio.
201 map_bh->b_page = &folio->page;
202 while (page_block < blocks_per_page) {
206 if (block_in_file < last_block) {
207 map_bh->b_size = (last_block-block_in_file) << blkbits;
208 if (args->get_block(inode, block_in_file, map_bh, 0))
210 args->first_logical_block = block_in_file;
213 if (!buffer_mapped(map_bh)) {
215 if (first_hole == blocks_per_page)
216 first_hole = page_block;
222 /* some filesystems will copy data into the page during
223 * the get_block call, in which case we don't want to
224 * read it again. map_buffer_to_folio copies the data
225 * we just collected from get_block into the folio's buffers
226 * so read_folio doesn't have to repeat the get_block call
228 if (buffer_uptodate(map_bh)) {
229 map_buffer_to_folio(folio, map_bh, page_block);
233 if (first_hole != blocks_per_page)
234 goto confused; /* hole -> non-hole */
236 /* Contiguous blocks? */
237 if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
239 nblocks = map_bh->b_size >> blkbits;
240 for (relative_block = 0; ; relative_block++) {
241 if (relative_block == nblocks) {
242 clear_buffer_mapped(map_bh);
244 } else if (page_block == blocks_per_page)
246 blocks[page_block] = map_bh->b_blocknr+relative_block;
250 bdev = map_bh->b_bdev;
253 if (first_hole != blocks_per_page) {
254 folio_zero_segment(folio, first_hole << blkbits, PAGE_SIZE);
255 if (first_hole == 0) {
256 folio_mark_uptodate(folio);
260 } else if (fully_mapped) {
261 folio_set_mappedtodisk(folio);
265 * This folio will go to BIO. Do we need to send this BIO off first?
267 if (args->bio && (args->last_block_in_bio != blocks[0] - 1))
268 args->bio = mpage_bio_submit(args->bio);
271 if (args->bio == NULL) {
272 if (first_hole == blocks_per_page) {
273 if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
277 args->bio = bio_alloc(bdev, bio_max_segs(args->nr_pages), op,
279 if (args->bio == NULL)
281 args->bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
284 length = first_hole << blkbits;
285 if (!bio_add_folio(args->bio, folio, length, 0)) {
286 args->bio = mpage_bio_submit(args->bio);
290 relative_block = block_in_file - args->first_logical_block;
291 nblocks = map_bh->b_size >> blkbits;
292 if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
293 (first_hole != blocks_per_page))
294 args->bio = mpage_bio_submit(args->bio);
296 args->last_block_in_bio = blocks[blocks_per_page - 1];
302 args->bio = mpage_bio_submit(args->bio);
303 if (!folio_test_uptodate(folio))
304 block_read_full_folio(folio, args->get_block);
311 * mpage_readahead - start reads against pages
312 * @rac: Describes which pages to read.
313 * @get_block: The filesystem's block mapper function.
315 * This function walks the pages and the blocks within each page, building and
316 * emitting large BIOs.
318 * If anything unusual happens, such as:
320 * - encountering a page which has buffers
321 * - encountering a page which has a non-hole after a hole
322 * - encountering a page with non-contiguous blocks
324 * then this code just gives up and calls the buffer_head-based read function.
325 * It does handle a page which has holes at the end - that is a common case:
326 * the end-of-file on blocksize < PAGE_SIZE setups.
328 * BH_Boundary explanation:
330 * There is a problem. The mpage read code assembles several pages, gets all
331 * their disk mappings, and then submits them all. That's fine, but obtaining
332 * the disk mappings may require I/O. Reads of indirect blocks, for example.
334 * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
335 * submitted in the following order:
337 * 12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
339 * because the indirect block has to be read to get the mappings of blocks
340 * 13,14,15,16. Obviously, this impacts performance.
342 * So what we do it to allow the filesystem's get_block() function to set
343 * BH_Boundary when it maps block 11. BH_Boundary says: mapping of the block
344 * after this one will require I/O against a block which is probably close to
345 * this one. So you should push what I/O you have currently accumulated.
347 * This all causes the disk requests to be issued in the correct order.
349 void mpage_readahead(struct readahead_control *rac, get_block_t get_block)
352 struct mpage_readpage_args args = {
353 .get_block = get_block,
354 .is_readahead = true,
357 while ((folio = readahead_folio(rac))) {
358 prefetchw(&folio->flags);
360 args.nr_pages = readahead_count(rac);
361 args.bio = do_mpage_readpage(&args);
364 mpage_bio_submit(args.bio);
366 EXPORT_SYMBOL(mpage_readahead);
369 * This isn't called much at all
371 int mpage_read_folio(struct folio *folio, get_block_t get_block)
373 struct mpage_readpage_args args = {
376 .get_block = get_block,
379 args.bio = do_mpage_readpage(&args);
381 mpage_bio_submit(args.bio);
384 EXPORT_SYMBOL(mpage_read_folio);
387 * Writing is not so simple.
389 * If the page has buffers then they will be used for obtaining the disk
390 * mapping. We only support pages which are fully mapped-and-dirty, with a
391 * special case for pages which are unmapped at the end: end-of-file.
393 * If the page has no buffers (preferred) then the page is mapped here.
395 * If all blocks are found to be contiguous then the page can go into the
396 * BIO. Otherwise fall back to the mapping's writepage().
398 * FIXME: This code wants an estimate of how many pages are still to be
399 * written, so it can intelligently allocate a suitably-sized BIO. For now,
400 * just allocate full-size (16-page) BIOs.
405 sector_t last_block_in_bio;
406 get_block_t *get_block;
407 unsigned use_writepage;
411 * We have our BIO, so we can now mark the buffers clean. Make
412 * sure to only clean buffers which we know we'll be writing.
414 static void clean_buffers(struct page *page, unsigned first_unmapped)
416 unsigned buffer_counter = 0;
417 struct buffer_head *bh, *head;
418 if (!page_has_buffers(page))
420 head = page_buffers(page);
424 if (buffer_counter++ == first_unmapped)
426 clear_buffer_dirty(bh);
427 bh = bh->b_this_page;
428 } while (bh != head);
431 * we cannot drop the bh if the page is not uptodate or a concurrent
432 * read_folio would fail to serialize with the bh and it would read from
433 * disk before we reach the platter.
435 if (buffer_heads_over_limit && PageUptodate(page))
436 try_to_free_buffers(page_folio(page));
440 * For situations where we want to clean all buffers attached to a page.
441 * We don't need to calculate how many buffers are attached to the page,
442 * we just need to specify a number larger than the maximum number of buffers.
444 void clean_page_buffers(struct page *page)
446 clean_buffers(page, ~0U);
449 static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
452 struct mpage_data *mpd = data;
453 struct bio *bio = mpd->bio;
454 struct address_space *mapping = page->mapping;
455 struct inode *inode = page->mapping->host;
456 const unsigned blkbits = inode->i_blkbits;
457 unsigned long end_index;
458 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
460 sector_t block_in_file;
461 sector_t blocks[MAX_BUF_PER_PAGE];
463 unsigned first_unmapped = blocks_per_page;
464 struct block_device *bdev = NULL;
466 sector_t boundary_block = 0;
467 struct block_device *boundary_bdev = NULL;
469 struct buffer_head map_bh;
470 loff_t i_size = i_size_read(inode);
473 if (page_has_buffers(page)) {
474 struct buffer_head *head = page_buffers(page);
475 struct buffer_head *bh = head;
477 /* If they're all mapped and dirty, do it */
480 BUG_ON(buffer_locked(bh));
481 if (!buffer_mapped(bh)) {
483 * unmapped dirty buffers are created by
484 * block_dirty_folio -> mmapped data
486 if (buffer_dirty(bh))
488 if (first_unmapped == blocks_per_page)
489 first_unmapped = page_block;
493 if (first_unmapped != blocks_per_page)
494 goto confused; /* hole -> non-hole */
496 if (!buffer_dirty(bh) || !buffer_uptodate(bh))
499 if (bh->b_blocknr != blocks[page_block-1] + 1)
502 blocks[page_block++] = bh->b_blocknr;
503 boundary = buffer_boundary(bh);
505 boundary_block = bh->b_blocknr;
506 boundary_bdev = bh->b_bdev;
509 } while ((bh = bh->b_this_page) != head);
515 * Page has buffers, but they are all unmapped. The page was
516 * created by pagein or read over a hole which was handled by
517 * block_read_full_folio(). If this address_space is also
518 * using mpage_readahead then this can rarely happen.
524 * The page has no buffers: map it to disk
526 BUG_ON(!PageUptodate(page));
527 block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
528 last_block = (i_size - 1) >> blkbits;
529 map_bh.b_page = page;
530 for (page_block = 0; page_block < blocks_per_page; ) {
533 map_bh.b_size = 1 << blkbits;
534 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
536 if (buffer_new(&map_bh))
537 clean_bdev_bh_alias(&map_bh);
538 if (buffer_boundary(&map_bh)) {
539 boundary_block = map_bh.b_blocknr;
540 boundary_bdev = map_bh.b_bdev;
543 if (map_bh.b_blocknr != blocks[page_block-1] + 1)
546 blocks[page_block++] = map_bh.b_blocknr;
547 boundary = buffer_boundary(&map_bh);
548 bdev = map_bh.b_bdev;
549 if (block_in_file == last_block)
553 BUG_ON(page_block == 0);
555 first_unmapped = page_block;
558 end_index = i_size >> PAGE_SHIFT;
559 if (page->index >= end_index) {
561 * The page straddles i_size. It must be zeroed out on each
562 * and every writepage invocation because it may be mmapped.
563 * "A file is mapped in multiples of the page size. For a file
564 * that is not a multiple of the page size, the remaining memory
565 * is zeroed when mapped, and writes to that region are not
566 * written out to the file."
568 unsigned offset = i_size & (PAGE_SIZE - 1);
570 if (page->index > end_index || !offset)
572 zero_user_segment(page, offset, PAGE_SIZE);
576 * This page will go to BIO. Do we need to send this BIO off first?
578 if (bio && mpd->last_block_in_bio != blocks[0] - 1)
579 bio = mpage_bio_submit(bio);
583 if (first_unmapped == blocks_per_page) {
584 if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
588 bio = bio_alloc(bdev, BIO_MAX_VECS,
589 REQ_OP_WRITE | wbc_to_write_flags(wbc),
591 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
592 wbc_init_bio(wbc, bio);
596 * Must try to add the page before marking the buffer clean or
597 * the confused fail path above (OOM) will be very confused when
598 * it finds all bh marked clean (i.e. it will not write anything)
600 wbc_account_cgroup_owner(wbc, page, PAGE_SIZE);
601 length = first_unmapped << blkbits;
602 if (bio_add_page(bio, page, length, 0) < length) {
603 bio = mpage_bio_submit(bio);
607 clean_buffers(page, first_unmapped);
609 BUG_ON(PageWriteback(page));
610 set_page_writeback(page);
612 if (boundary || (first_unmapped != blocks_per_page)) {
613 bio = mpage_bio_submit(bio);
614 if (boundary_block) {
615 write_boundary_block(boundary_bdev,
616 boundary_block, 1 << blkbits);
619 mpd->last_block_in_bio = blocks[blocks_per_page - 1];
625 bio = mpage_bio_submit(bio);
627 if (mpd->use_writepage) {
628 ret = mapping->a_ops->writepage(page, wbc);
634 * The caller has a ref on the inode, so *mapping is stable
636 mapping_set_error(mapping, ret);
643 * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
644 * @mapping: address space structure to write
645 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
646 * @get_block: the filesystem's block mapper function.
647 * If this is NULL then use a_ops->writepage. Otherwise, go
650 * This is a library function, which implements the writepages()
651 * address_space_operation.
653 * If a page is already under I/O, generic_writepages() skips it, even
654 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
655 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
656 * and msync() need to guarantee that all the data which was dirty at the time
657 * the call was made get new I/O started against them. If wbc->sync_mode is
658 * WB_SYNC_ALL then we were called for data integrity and we must wait for
659 * existing IO to complete.
662 mpage_writepages(struct address_space *mapping,
663 struct writeback_control *wbc, get_block_t get_block)
665 struct blk_plug plug;
668 blk_start_plug(&plug);
671 ret = generic_writepages(mapping, wbc);
673 struct mpage_data mpd = {
675 .last_block_in_bio = 0,
676 .get_block = get_block,
680 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
682 mpage_bio_submit(mpd.bio);
684 blk_finish_plug(&plug);
687 EXPORT_SYMBOL(mpage_writepages);
689 int mpage_writepage(struct page *page, get_block_t get_block,
690 struct writeback_control *wbc)
692 struct mpage_data mpd = {
694 .last_block_in_bio = 0,
695 .get_block = get_block,
698 int ret = __mpage_writepage(page, wbc, &mpd);
700 mpage_bio_submit(mpd.bio);
703 EXPORT_SYMBOL(mpage_writepage);