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_read_end_io(struct bio *bio)
49 int err = blk_status_to_errno(bio->bi_status);
51 bio_for_each_folio_all(fi, bio) {
53 folio_set_error(fi.folio);
55 folio_mark_uptodate(fi.folio);
56 folio_unlock(fi.folio);
62 static void mpage_write_end_io(struct bio *bio)
65 int err = blk_status_to_errno(bio->bi_status);
67 bio_for_each_folio_all(fi, bio) {
69 folio_set_error(fi.folio);
70 mapping_set_error(fi.folio->mapping, err);
72 folio_end_writeback(fi.folio);
78 static struct bio *mpage_bio_submit_read(struct bio *bio)
80 bio->bi_end_io = mpage_read_end_io;
86 static struct bio *mpage_bio_submit_write(struct bio *bio)
88 bio->bi_end_io = mpage_write_end_io;
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
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.
104 static void map_buffer_to_folio(struct folio *folio, struct buffer_head *bh,
107 struct inode *inode = folio->mapping->host;
108 struct buffer_head *page_bh, *head;
111 head = folio_buffers(folio);
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
117 if (inode->i_blkbits == PAGE_SHIFT &&
118 buffer_uptodate(bh)) {
119 folio_mark_uptodate(folio);
122 head = create_empty_buffers(folio, i_blocksize(inode), 0);
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;
133 page_bh = page_bh->b_this_page;
135 } while (page_bh != head);
138 struct mpage_readpage_args {
141 unsigned int nr_pages;
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;
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.
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
158 static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
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;
168 sector_t last_block_in_file;
169 sector_t blocks[MAX_BUF_PER_PAGE];
171 unsigned first_hole = blocks_per_page;
172 struct block_device *bdev = NULL;
174 int fully_mapped = 1;
175 blk_opf_t opf = REQ_OP_READ;
177 unsigned relative_block;
178 gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
180 /* MAX_BUF_PER_PAGE, for example */
181 VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
183 if (args->is_readahead) {
185 gfp |= __GFP_NORETRY | __GFP_NOWARN;
188 if (folio_buffers(folio))
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;
199 * Map blocks using the result from the previous get_blocks call first.
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;
208 for (relative_block = 0; ; relative_block++) {
209 if (relative_block == last) {
210 clear_buffer_mapped(map_bh);
213 if (page_block == blocks_per_page)
215 blocks[page_block] = map_bh->b_blocknr + map_offset +
220 bdev = map_bh->b_bdev;
224 * Then do more get_blocks calls until we are done with this folio.
226 map_bh->b_folio = folio;
227 while (page_block < blocks_per_page) {
231 if (block_in_file < last_block) {
232 map_bh->b_size = (last_block-block_in_file) << blkbits;
233 if (args->get_block(inode, block_in_file, map_bh, 0))
235 args->first_logical_block = block_in_file;
238 if (!buffer_mapped(map_bh)) {
240 if (first_hole == blocks_per_page)
241 first_hole = page_block;
247 /* some filesystems will copy data into the page during
248 * the get_block call, in which case we don't want to
249 * read it again. map_buffer_to_folio copies the data
250 * we just collected from get_block into the folio's buffers
251 * so read_folio doesn't have to repeat the get_block call
253 if (buffer_uptodate(map_bh)) {
254 map_buffer_to_folio(folio, map_bh, page_block);
258 if (first_hole != blocks_per_page)
259 goto confused; /* hole -> non-hole */
261 /* Contiguous blocks? */
262 if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
264 nblocks = map_bh->b_size >> blkbits;
265 for (relative_block = 0; ; relative_block++) {
266 if (relative_block == nblocks) {
267 clear_buffer_mapped(map_bh);
269 } else if (page_block == blocks_per_page)
271 blocks[page_block] = map_bh->b_blocknr+relative_block;
275 bdev = map_bh->b_bdev;
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);
285 } else if (fully_mapped) {
286 folio_set_mappedtodisk(folio);
290 * This folio will go to BIO. Do we need to send this BIO off first?
292 if (args->bio && (args->last_block_in_bio != blocks[0] - 1))
293 args->bio = mpage_bio_submit_read(args->bio);
296 if (args->bio == NULL) {
297 args->bio = bio_alloc(bdev, bio_max_segs(args->nr_pages), opf,
299 if (args->bio == NULL)
301 args->bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
304 length = first_hole << blkbits;
305 if (!bio_add_folio(args->bio, folio, length, 0)) {
306 args->bio = mpage_bio_submit_read(args->bio);
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);
316 args->last_block_in_bio = blocks[blocks_per_page - 1];
322 args->bio = mpage_bio_submit_read(args->bio);
323 if (!folio_test_uptodate(folio))
324 block_read_full_folio(folio, args->get_block);
331 * mpage_readahead - start reads against pages
332 * @rac: Describes which pages to read.
333 * @get_block: The filesystem's block mapper function.
335 * This function walks the pages and the blocks within each page, building and
336 * emitting large BIOs.
338 * If anything unusual happens, such as:
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
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.
348 * BH_Boundary explanation:
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.
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:
357 * 12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
359 * because the indirect block has to be read to get the mappings of blocks
360 * 13,14,15,16. Obviously, this impacts performance.
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.
367 * This all causes the disk requests to be issued in the correct order.
369 void mpage_readahead(struct readahead_control *rac, get_block_t get_block)
372 struct mpage_readpage_args args = {
373 .get_block = get_block,
374 .is_readahead = true,
377 while ((folio = readahead_folio(rac))) {
378 prefetchw(&folio->flags);
380 args.nr_pages = readahead_count(rac);
381 args.bio = do_mpage_readpage(&args);
384 mpage_bio_submit_read(args.bio);
386 EXPORT_SYMBOL(mpage_readahead);
389 * This isn't called much at all
391 int mpage_read_folio(struct folio *folio, get_block_t get_block)
393 struct mpage_readpage_args args = {
396 .get_block = get_block,
399 args.bio = do_mpage_readpage(&args);
401 mpage_bio_submit_read(args.bio);
404 EXPORT_SYMBOL(mpage_read_folio);
407 * Writing is not so simple.
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.
413 * If the page has no buffers (preferred) then the page is mapped here.
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().
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.
425 sector_t last_block_in_bio;
426 get_block_t *get_block;
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.
433 static void clean_buffers(struct page *page, unsigned first_unmapped)
435 unsigned buffer_counter = 0;
436 struct buffer_head *bh, *head;
437 if (!page_has_buffers(page))
439 head = page_buffers(page);
443 if (buffer_counter++ == first_unmapped)
445 clear_buffer_dirty(bh);
446 bh = bh->b_this_page;
447 } while (bh != head);
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.
454 if (buffer_heads_over_limit && PageUptodate(page))
455 try_to_free_buffers(page_folio(page));
459 * For situations where we want to clean all buffers attached to a page.
460 * We don't need to calculate how many buffers are attached to the page,
461 * we just need to specify a number larger than the maximum number of buffers.
463 void clean_page_buffers(struct page *page)
465 clean_buffers(page, ~0U);
468 static int __mpage_writepage(struct folio *folio, struct writeback_control *wbc,
471 struct mpage_data *mpd = data;
472 struct bio *bio = mpd->bio;
473 struct address_space *mapping = folio->mapping;
474 struct inode *inode = mapping->host;
475 const unsigned blkbits = inode->i_blkbits;
476 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
478 sector_t block_in_file;
479 sector_t blocks[MAX_BUF_PER_PAGE];
481 unsigned first_unmapped = blocks_per_page;
482 struct block_device *bdev = NULL;
484 sector_t boundary_block = 0;
485 struct block_device *boundary_bdev = NULL;
487 struct buffer_head map_bh;
488 loff_t i_size = i_size_read(inode);
490 struct buffer_head *head = folio_buffers(folio);
493 struct buffer_head *bh = head;
495 /* If they're all mapped and dirty, do it */
498 BUG_ON(buffer_locked(bh));
499 if (!buffer_mapped(bh)) {
501 * unmapped dirty buffers are created by
502 * block_dirty_folio -> mmapped data
504 if (buffer_dirty(bh))
506 if (first_unmapped == blocks_per_page)
507 first_unmapped = page_block;
511 if (first_unmapped != blocks_per_page)
512 goto confused; /* hole -> non-hole */
514 if (!buffer_dirty(bh) || !buffer_uptodate(bh))
517 if (bh->b_blocknr != blocks[page_block-1] + 1)
520 blocks[page_block++] = bh->b_blocknr;
521 boundary = buffer_boundary(bh);
523 boundary_block = bh->b_blocknr;
524 boundary_bdev = bh->b_bdev;
527 } while ((bh = bh->b_this_page) != head);
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_folio(). If this address_space is also
536 * using mpage_readahead then this can rarely happen.
542 * The page has no buffers: map it to disk
544 BUG_ON(!folio_test_uptodate(folio));
545 block_in_file = (sector_t)folio->index << (PAGE_SHIFT - blkbits);
547 * Whole page beyond EOF? Skip allocating blocks to avoid leaking
550 if (block_in_file >= (i_size + (1 << blkbits) - 1) >> blkbits)
552 last_block = (i_size - 1) >> blkbits;
553 map_bh.b_folio = folio;
554 for (page_block = 0; page_block < blocks_per_page; ) {
557 map_bh.b_size = 1 << blkbits;
558 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
560 if (!buffer_mapped(&map_bh))
562 if (buffer_new(&map_bh))
563 clean_bdev_bh_alias(&map_bh);
564 if (buffer_boundary(&map_bh)) {
565 boundary_block = map_bh.b_blocknr;
566 boundary_bdev = map_bh.b_bdev;
569 if (map_bh.b_blocknr != blocks[page_block-1] + 1)
572 blocks[page_block++] = map_bh.b_blocknr;
573 boundary = buffer_boundary(&map_bh);
574 bdev = map_bh.b_bdev;
575 if (block_in_file == last_block)
579 BUG_ON(page_block == 0);
581 first_unmapped = page_block;
584 /* Don't bother writing beyond EOF, truncate will discard the folio */
585 if (folio_pos(folio) >= i_size)
587 length = folio_size(folio);
588 if (folio_pos(folio) + length > i_size) {
590 * The page straddles i_size. It must be zeroed out on each
591 * and every writepage invocation because it may be mmapped.
592 * "A file is mapped in multiples of the page size. For a file
593 * that is not a multiple of the page size, the remaining memory
594 * is zeroed when mapped, and writes to that region are not
595 * written out to the file."
597 length = i_size - folio_pos(folio);
598 folio_zero_segment(folio, length, folio_size(folio));
602 * This page will go to BIO. Do we need to send this BIO off first?
604 if (bio && mpd->last_block_in_bio != blocks[0] - 1)
605 bio = mpage_bio_submit_write(bio);
609 bio = bio_alloc(bdev, BIO_MAX_VECS,
610 REQ_OP_WRITE | wbc_to_write_flags(wbc),
612 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
613 wbc_init_bio(wbc, bio);
617 * Must try to add the page before marking the buffer clean or
618 * the confused fail path above (OOM) will be very confused when
619 * it finds all bh marked clean (i.e. it will not write anything)
621 wbc_account_cgroup_owner(wbc, &folio->page, folio_size(folio));
622 length = first_unmapped << blkbits;
623 if (!bio_add_folio(bio, folio, length, 0)) {
624 bio = mpage_bio_submit_write(bio);
628 clean_buffers(&folio->page, first_unmapped);
630 BUG_ON(folio_test_writeback(folio));
631 folio_start_writeback(folio);
633 if (boundary || (first_unmapped != blocks_per_page)) {
634 bio = mpage_bio_submit_write(bio);
635 if (boundary_block) {
636 write_boundary_block(boundary_bdev,
637 boundary_block, 1 << blkbits);
640 mpd->last_block_in_bio = blocks[blocks_per_page - 1];
646 bio = mpage_bio_submit_write(bio);
649 * The caller has a ref on the inode, so *mapping is stable
651 ret = block_write_full_page(&folio->page, mpd->get_block, wbc);
652 mapping_set_error(mapping, ret);
659 * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
660 * @mapping: address space structure to write
661 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
662 * @get_block: the filesystem's block mapper function.
664 * This is a library function, which implements the writepages()
665 * address_space_operation.
668 mpage_writepages(struct address_space *mapping,
669 struct writeback_control *wbc, get_block_t get_block)
671 struct mpage_data mpd = {
672 .get_block = get_block,
674 struct blk_plug plug;
677 blk_start_plug(&plug);
678 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
680 mpage_bio_submit_write(mpd.bio);
681 blk_finish_plug(&plug);
684 EXPORT_SYMBOL(mpage_writepages);