4 * Copyright (C) 2002, Linus Torvalds.
6 * Contains functions related to preparing and submitting BIOs which contain
7 * multiple pagecache pages.
9 * 15May2002 akpm@zip.com.au
11 * 27Jun2002 axboe@suse.de
12 * use bio_add_page() to build bio's just the right size
15 #include <linux/kernel.h>
16 #include <linux/module.h>
18 #include <linux/kdev_t.h>
19 #include <linux/bio.h>
21 #include <linux/buffer_head.h>
22 #include <linux/blkdev.h>
23 #include <linux/highmem.h>
24 #include <linux/prefetch.h>
25 #include <linux/mpage.h>
26 #include <linux/writeback.h>
27 #include <linux/backing-dev.h>
28 #include <linux/pagevec.h>
31 * I/O completion handler for multipage BIOs.
33 * The mpage code never puts partial pages into a BIO (except for end-of-file).
34 * If a page does not map to a contiguous run of blocks then it simply falls
35 * back to block_read_full_page().
37 * Why is this? If a page's completion depends on a number of different BIOs
38 * which can complete in any order (or at the same time) then determining the
39 * status of that page is hard. See end_buffer_async_read() for the details.
40 * There is no point in duplicating all that complexity.
42 static int mpage_end_io_read(struct bio *bio, unsigned int bytes_done, int err)
44 const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
45 struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
51 struct page *page = bvec->bv_page;
53 if (--bvec >= bio->bi_io_vec)
54 prefetchw(&bvec->bv_page->flags);
57 SetPageUptodate(page);
59 ClearPageUptodate(page);
63 } while (bvec >= bio->bi_io_vec);
68 static int mpage_end_io_write(struct bio *bio, unsigned int bytes_done, int err)
70 const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
71 struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
77 struct page *page = bvec->bv_page;
79 if (--bvec >= bio->bi_io_vec)
80 prefetchw(&bvec->bv_page->flags);
84 end_page_writeback(page);
85 } while (bvec >= bio->bi_io_vec);
90 struct bio *mpage_bio_submit(int rw, struct bio *bio)
92 bio->bi_end_io = mpage_end_io_read;
94 bio->bi_end_io = mpage_end_io_write;
100 mpage_alloc(struct block_device *bdev,
101 sector_t first_sector, int nr_vecs, int gfp_flags)
105 bio = bio_alloc(gfp_flags, nr_vecs);
107 if (bio == NULL && (current->flags & PF_MEMALLOC)) {
108 while (!bio && (nr_vecs /= 2))
109 bio = bio_alloc(gfp_flags, nr_vecs);
114 bio->bi_sector = first_sector;
120 * support function for mpage_readpages. The fs supplied get_block might
121 * return an up to date buffer. This is used to map that buffer into
122 * the page, which allows readpage to avoid triggering a duplicate call
125 * The idea is to avoid adding buffers to pages that don't already have
126 * them. So when the buffer is up to date and the page size == block size,
127 * this marks the page up to date instead of adding new buffers.
130 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
132 struct inode *inode = page->mapping->host;
133 struct buffer_head *page_bh, *head;
136 if (!page_has_buffers(page)) {
138 * don't make any buffers if there is only one buffer on
139 * the page and the page just needs to be set up to date
141 if (inode->i_blkbits == PAGE_CACHE_SHIFT &&
142 buffer_uptodate(bh)) {
143 SetPageUptodate(page);
146 create_empty_buffers(page, 1 << inode->i_blkbits, 0);
148 head = page_buffers(page);
151 if (block == page_block) {
152 page_bh->b_state = bh->b_state;
153 page_bh->b_bdev = bh->b_bdev;
154 page_bh->b_blocknr = bh->b_blocknr;
157 page_bh = page_bh->b_this_page;
159 } while (page_bh != head);
163 * mpage_readpages - populate an address space with some pages, and
164 * start reads against them.
166 * @mapping: the address_space
167 * @pages: The address of a list_head which contains the target pages. These
168 * pages have their ->index populated and are otherwise uninitialised.
170 * The page at @pages->prev has the lowest file offset, and reads should be
171 * issued in @pages->prev to @pages->next order.
173 * @nr_pages: The number of pages at *@pages
174 * @get_block: The filesystem's block mapper function.
176 * This function walks the pages and the blocks within each page, building and
177 * emitting large BIOs.
179 * If anything unusual happens, such as:
181 * - encountering a page which has buffers
182 * - encountering a page which has a non-hole after a hole
183 * - encountering a page with non-contiguous blocks
185 * then this code just gives up and calls the buffer_head-based read function.
186 * It does handle a page which has holes at the end - that is a common case:
187 * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
189 * BH_Boundary explanation:
191 * There is a problem. The mpage read code assembles several pages, gets all
192 * their disk mappings, and then submits them all. That's fine, but obtaining
193 * the disk mappings may require I/O. Reads of indirect blocks, for example.
195 * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
196 * submitted in the following order:
197 * 12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
198 * because the indirect block has to be read to get the mappings of blocks
199 * 13,14,15,16. Obviously, this impacts performance.
201 * So what we do it to allow the filesystem's get_block() function to set
202 * BH_Boundary when it maps block 11. BH_Boundary says: mapping of the block
203 * after this one will require I/O against a block which is probably close to
204 * this one. So you should push what I/O you have currently accumulated.
206 * This all causes the disk requests to be issued in the correct order.
209 do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
210 sector_t *last_block_in_bio, get_block_t get_block)
212 struct inode *inode = page->mapping->host;
213 const unsigned blkbits = inode->i_blkbits;
214 const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
215 const unsigned blocksize = 1 << blkbits;
216 sector_t block_in_file;
218 sector_t blocks[MAX_BUF_PER_PAGE];
220 unsigned first_hole = blocks_per_page;
221 struct block_device *bdev = NULL;
222 struct buffer_head bh;
224 int fully_mapped = 1;
226 if (page_has_buffers(page))
229 block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits);
230 last_block = (i_size_read(inode) + blocksize - 1) >> blkbits;
233 for (page_block = 0; page_block < blocks_per_page;
234 page_block++, block_in_file++) {
236 if (block_in_file < last_block) {
237 if (get_block(inode, block_in_file, &bh, 0))
241 if (!buffer_mapped(&bh)) {
243 if (first_hole == blocks_per_page)
244 first_hole = page_block;
248 /* some filesystems will copy data into the page during
249 * the get_block call, in which case we don't want to
250 * read it again. map_buffer_to_page copies the data
251 * we just collected from get_block into the page's buffers
252 * so readpage doesn't have to repeat the get_block call
254 if (buffer_uptodate(&bh)) {
255 map_buffer_to_page(page, &bh, page_block);
259 if (first_hole != blocks_per_page)
260 goto confused; /* hole -> non-hole */
262 /* Contiguous blocks? */
263 if (page_block && blocks[page_block-1] != bh.b_blocknr-1)
265 blocks[page_block] = bh.b_blocknr;
269 if (first_hole != blocks_per_page) {
270 char *kaddr = kmap_atomic(page, KM_USER0);
271 memset(kaddr + (first_hole << blkbits), 0,
272 PAGE_CACHE_SIZE - (first_hole << blkbits));
273 flush_dcache_page(page);
274 kunmap_atomic(kaddr, KM_USER0);
275 if (first_hole == 0) {
276 SetPageUptodate(page);
280 } else if (fully_mapped) {
281 SetPageMappedToDisk(page);
285 * This page will go to BIO. Do we need to send this BIO off first?
287 if (bio && (*last_block_in_bio != blocks[0] - 1))
288 bio = mpage_bio_submit(READ, bio);
292 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
293 nr_pages, GFP_KERNEL);
298 length = first_hole << blkbits;
299 if (bio_add_page(bio, page, length, 0) < length) {
300 bio = mpage_bio_submit(READ, bio);
304 if (buffer_boundary(&bh) || (first_hole != blocks_per_page))
305 bio = mpage_bio_submit(READ, bio);
307 *last_block_in_bio = blocks[blocks_per_page - 1];
313 bio = mpage_bio_submit(READ, bio);
314 if (!PageUptodate(page))
315 block_read_full_page(page, get_block);
322 mpage_readpages(struct address_space *mapping, struct list_head *pages,
323 unsigned nr_pages, get_block_t get_block)
325 struct bio *bio = NULL;
327 sector_t last_block_in_bio = 0;
328 struct pagevec lru_pvec;
330 pagevec_init(&lru_pvec, 0);
331 for (page_idx = 0; page_idx < nr_pages; page_idx++) {
332 struct page *page = list_entry(pages->prev, struct page, lru);
334 prefetchw(&page->flags);
335 list_del(&page->lru);
336 if (!add_to_page_cache(page, mapping,
337 page->index, GFP_KERNEL)) {
338 bio = do_mpage_readpage(bio, page,
340 &last_block_in_bio, get_block);
341 if (!pagevec_add(&lru_pvec, page))
342 __pagevec_lru_add(&lru_pvec);
344 page_cache_release(page);
347 pagevec_lru_add(&lru_pvec);
348 BUG_ON(!list_empty(pages));
350 mpage_bio_submit(READ, bio);
353 EXPORT_SYMBOL(mpage_readpages);
356 * This isn't called much at all
358 int mpage_readpage(struct page *page, get_block_t get_block)
360 struct bio *bio = NULL;
361 sector_t last_block_in_bio = 0;
363 bio = do_mpage_readpage(bio, page, 1,
364 &last_block_in_bio, get_block);
366 mpage_bio_submit(READ, bio);
369 EXPORT_SYMBOL(mpage_readpage);
372 * Writing is not so simple.
374 * If the page has buffers then they will be used for obtaining the disk
375 * mapping. We only support pages which are fully mapped-and-dirty, with a
376 * special case for pages which are unmapped at the end: end-of-file.
378 * If the page has no buffers (preferred) then the page is mapped here.
380 * If all blocks are found to be contiguous then the page can go into the
381 * BIO. Otherwise fall back to the mapping's writepage().
383 * FIXME: This code wants an estimate of how many pages are still to be
384 * written, so it can intelligently allocate a suitably-sized BIO. For now,
385 * just allocate full-size (16-page) BIOs.
388 mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
389 sector_t *last_block_in_bio, int *ret, struct writeback_control *wbc)
391 struct address_space *mapping = page->mapping;
392 struct inode *inode = page->mapping->host;
393 const unsigned blkbits = inode->i_blkbits;
394 unsigned long end_index;
395 const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
397 sector_t block_in_file;
398 sector_t blocks[MAX_BUF_PER_PAGE];
400 unsigned first_unmapped = blocks_per_page;
401 struct block_device *bdev = NULL;
403 sector_t boundary_block = 0;
404 struct block_device *boundary_bdev = NULL;
406 struct buffer_head map_bh;
408 if (page_has_buffers(page)) {
409 struct buffer_head *head = page_buffers(page);
410 struct buffer_head *bh = head;
412 /* If they're all mapped and dirty, do it */
415 BUG_ON(buffer_locked(bh));
416 if (!buffer_mapped(bh)) {
418 * unmapped dirty buffers are created by
419 * __set_page_dirty_buffers -> mmapped data
421 if (buffer_dirty(bh))
423 if (first_unmapped == blocks_per_page)
424 first_unmapped = page_block;
428 if (first_unmapped != blocks_per_page)
429 goto confused; /* hole -> non-hole */
431 if (!buffer_dirty(bh) || !buffer_uptodate(bh))
434 if (bh->b_blocknr != blocks[page_block-1] + 1)
437 blocks[page_block++] = bh->b_blocknr;
438 boundary = buffer_boundary(bh);
440 boundary_block = bh->b_blocknr;
441 boundary_bdev = bh->b_bdev;
444 } while ((bh = bh->b_this_page) != head);
450 * Page has buffers, but they are all unmapped. The page was
451 * created by pagein or read over a hole which was handled by
452 * block_read_full_page(). If this address_space is also
453 * using mpage_readpages then this can rarely happen.
459 * The page has no buffers: map it to disk
461 BUG_ON(!PageUptodate(page));
462 block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits);
463 last_block = (i_size_read(inode) - 1) >> blkbits;
464 map_bh.b_page = page;
465 for (page_block = 0; page_block < blocks_per_page; ) {
468 if (get_block(inode, block_in_file, &map_bh, 1))
470 if (buffer_new(&map_bh))
471 unmap_underlying_metadata(map_bh.b_bdev,
473 if (buffer_boundary(&map_bh)) {
474 boundary_block = map_bh.b_blocknr;
475 boundary_bdev = map_bh.b_bdev;
478 if (map_bh.b_blocknr != blocks[page_block-1] + 1)
481 blocks[page_block++] = map_bh.b_blocknr;
482 boundary = buffer_boundary(&map_bh);
483 bdev = map_bh.b_bdev;
484 if (block_in_file == last_block)
488 BUG_ON(page_block == 0);
490 first_unmapped = page_block;
492 end_index = i_size_read(inode) >> PAGE_CACHE_SHIFT;
493 if (page->index >= end_index) {
494 unsigned offset = i_size_read(inode) & (PAGE_CACHE_SIZE - 1);
497 if (page->index > end_index || !offset)
499 kaddr = kmap_atomic(page, KM_USER0);
500 memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
501 flush_dcache_page(page);
502 kunmap_atomic(kaddr, KM_USER0);
508 * This page will go to BIO. Do we need to send this BIO off first?
510 if (bio && *last_block_in_bio != blocks[0] - 1)
511 bio = mpage_bio_submit(WRITE, bio);
515 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
516 bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
522 * OK, we have our BIO, so we can now mark the buffers clean. Make
523 * sure to only clean buffers which we know we'll be writing.
525 if (page_has_buffers(page)) {
526 struct buffer_head *head = page_buffers(page);
527 struct buffer_head *bh = head;
528 unsigned buffer_counter = 0;
531 if (buffer_counter++ == first_unmapped)
533 clear_buffer_dirty(bh);
534 bh = bh->b_this_page;
535 } while (bh != head);
537 if (buffer_heads_over_limit)
538 try_to_free_buffers(page);
541 length = first_unmapped << blkbits;
542 if (bio_add_page(bio, page, length, 0) < length) {
543 bio = mpage_bio_submit(WRITE, bio);
547 BUG_ON(PageWriteback(page));
548 set_page_writeback(page);
550 if (boundary || (first_unmapped != blocks_per_page)) {
551 bio = mpage_bio_submit(WRITE, bio);
552 if (boundary_block) {
553 write_boundary_block(boundary_bdev,
554 boundary_block, 1 << blkbits);
557 *last_block_in_bio = blocks[blocks_per_page - 1];
563 bio = mpage_bio_submit(WRITE, bio);
564 *ret = page->mapping->a_ops->writepage(page, wbc);
566 * The caller has a ref on the inode, so *mapping is stable
570 set_bit(AS_ENOSPC, &mapping->flags);
572 set_bit(AS_EIO, &mapping->flags);
579 * mpage_writepages - walk the list of dirty pages of the given
580 * address space and writepage() all of them.
582 * @mapping: address space structure to write
583 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
584 * @get_block: the filesystem's block mapper function.
585 * If this is NULL then use a_ops->writepage. Otherwise, go
588 * This is a library function, which implements the writepages()
589 * address_space_operation.
591 * If a page is already under I/O, generic_writepages() skips it, even
592 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
593 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
594 * and msync() need to guarantee that all the data which was dirty at the time
595 * the call was made get new I/O started against them. If wbc->sync_mode is
596 * WB_SYNC_ALL then we were called for data integrity and we must wait for
597 * existing IO to complete.
600 mpage_writepages(struct address_space *mapping,
601 struct writeback_control *wbc, get_block_t get_block)
603 struct backing_dev_info *bdi = mapping->backing_dev_info;
604 struct bio *bio = NULL;
605 sector_t last_block_in_bio = 0;
608 int (*writepage)(struct page *page, struct writeback_control *wbc);
614 if (wbc->nonblocking && bdi_write_congested(bdi)) {
615 wbc->encountered_congestion = 1;
620 if (get_block == NULL)
621 writepage = mapping->a_ops->writepage;
623 pagevec_init(&pvec, 0);
624 if (wbc->sync_mode == WB_SYNC_NONE) {
625 index = mapping->writeback_index; /* Start from prev offset */
627 index = 0; /* whole-file sweep */
631 while (!done && (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
632 PAGECACHE_TAG_DIRTY, PAGEVEC_SIZE))) {
636 for (i = 0; i < nr_pages; i++) {
637 struct page *page = pvec.pages[i];
640 * At this point we hold neither mapping->tree_lock nor
641 * lock on the page itself: the page may be truncated or
642 * invalidated (changing page->mapping to NULL), or even
643 * swizzled back from swapper_space to tmpfs file
649 if (wbc->sync_mode != WB_SYNC_NONE)
650 wait_on_page_writeback(page);
652 if (page->mapping != mapping || PageWriteback(page) ||
653 !clear_page_dirty_for_io(page)) {
659 ret = (*writepage)(page, wbc);
669 bio = mpage_writepage(bio, page, get_block,
670 &last_block_in_bio, &ret, wbc);
672 if (ret || (--(wbc->nr_to_write) <= 0))
674 if (wbc->nonblocking && bdi_write_congested(bdi)) {
675 wbc->encountered_congestion = 1;
679 pagevec_release(&pvec);
682 if (!scanned && !done) {
684 * We hit the last page and there is more work to be done: wrap
685 * back to the start of the file
691 mapping->writeback_index = index;
693 mpage_bio_submit(WRITE, bio);
696 EXPORT_SYMBOL(mpage_writepages);