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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/*
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/module.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/writeback.h>
28#include <linux/backing-dev.h>
29#include <linux/pagevec.h>
30#include <linux/cleancache.h>
31
32/*
33 * I/O completion handler for multipage BIOs.
34 *
35 * The mpage code never puts partial pages into a BIO (except for end-of-file).
36 * If a page does not map to a contiguous run of blocks then it simply falls
37 * back to block_read_full_page().
38 *
39 * Why is this? If a page's completion depends on a number of different BIOs
40 * which can complete in any order (or at the same time) then determining the
41 * status of that page is hard. See end_buffer_async_read() for the details.
42 * There is no point in duplicating all that complexity.
43 */
44static void mpage_end_io(struct bio *bio, int err)
45{
46 const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
47 struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
48
49 do {
50 struct page *page = bvec->bv_page;
51
52 if (--bvec >= bio->bi_io_vec)
53 prefetchw(&bvec->bv_page->flags);
54 if (bio_data_dir(bio) == READ) {
55 if (uptodate) {
56 SetPageUptodate(page);
57 } else {
58 ClearPageUptodate(page);
59 SetPageError(page);
60 }
61 unlock_page(page);
62 } else { /* bio_data_dir(bio) == WRITE */
63 if (!uptodate) {
64 SetPageError(page);
65 if (page->mapping)
66 set_bit(AS_EIO, &page->mapping->flags);
67 }
68 end_page_writeback(page);
69 }
70 } while (bvec >= bio->bi_io_vec);
71 bio_put(bio);
72}
73
74static struct bio *mpage_bio_submit(int rw, struct bio *bio)
75{
76 bio->bi_end_io = mpage_end_io;
77 submit_bio(rw, bio);
78 return NULL;
79}
80
81static struct bio *
82mpage_alloc(struct block_device *bdev,
83 sector_t first_sector, int nr_vecs,
84 gfp_t gfp_flags)
85{
86 struct bio *bio;
87
88 bio = bio_alloc(gfp_flags, nr_vecs);
89
90 if (bio == NULL && (current->flags & PF_MEMALLOC)) {
91 while (!bio && (nr_vecs /= 2))
92 bio = bio_alloc(gfp_flags, nr_vecs);
93 }
94
95 if (bio) {
96 bio->bi_bdev = bdev;
97 bio->bi_sector = first_sector;
98 }
99 return bio;
100}
101
102/*
103 * support function for mpage_readpages. The fs supplied get_block might
104 * return an up to date buffer. This is used to map that buffer into
105 * the page, which allows readpage to avoid triggering a duplicate call
106 * to get_block.
107 *
108 * The idea is to avoid adding buffers to pages that don't already have
109 * them. So when the buffer is up to date and the page size == block size,
110 * this marks the page up to date instead of adding new buffers.
111 */
112static void
113map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
114{
115 struct inode *inode = page->mapping->host;
116 struct buffer_head *page_bh, *head;
117 int block = 0;
118
119 if (!page_has_buffers(page)) {
120 /*
121 * don't make any buffers if there is only one buffer on
122 * the page and the page just needs to be set up to date
123 */
124 if (inode->i_blkbits == PAGE_CACHE_SHIFT &&
125 buffer_uptodate(bh)) {
126 SetPageUptodate(page);
127 return;
128 }
129 create_empty_buffers(page, 1 << inode->i_blkbits, 0);
130 }
131 head = page_buffers(page);
132 page_bh = head;
133 do {
134 if (block == page_block) {
135 page_bh->b_state = bh->b_state;
136 page_bh->b_bdev = bh->b_bdev;
137 page_bh->b_blocknr = bh->b_blocknr;
138 break;
139 }
140 page_bh = page_bh->b_this_page;
141 block++;
142 } while (page_bh != head);
143}
144
145/*
146 * This is the worker routine which does all the work of mapping the disk
147 * blocks and constructs largest possible bios, submits them for IO if the
148 * blocks are not contiguous on the disk.
149 *
150 * We pass a buffer_head back and forth and use its buffer_mapped() flag to
151 * represent the validity of its disk mapping and to decide when to do the next
152 * get_block() call.
153 */
154static struct bio *
155do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
156 sector_t *last_block_in_bio, struct buffer_head *map_bh,
157 unsigned long *first_logical_block, get_block_t get_block)
158{
159 struct inode *inode = page->mapping->host;
160 const unsigned blkbits = inode->i_blkbits;
161 const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
162 const unsigned blocksize = 1 << blkbits;
163 sector_t block_in_file;
164 sector_t last_block;
165 sector_t last_block_in_file;
166 sector_t blocks[MAX_BUF_PER_PAGE];
167 unsigned page_block;
168 unsigned first_hole = blocks_per_page;
169 struct block_device *bdev = NULL;
170 int length;
171 int fully_mapped = 1;
172 unsigned nblocks;
173 unsigned relative_block;
174
175 if (page_has_buffers(page))
176 goto confused;
177
178 block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
179 last_block = block_in_file + nr_pages * blocks_per_page;
180 last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
181 if (last_block > last_block_in_file)
182 last_block = last_block_in_file;
183 page_block = 0;
184
185 /*
186 * Map blocks using the result from the previous get_blocks call first.
187 */
188 nblocks = map_bh->b_size >> blkbits;
189 if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
190 block_in_file < (*first_logical_block + nblocks)) {
191 unsigned map_offset = block_in_file - *first_logical_block;
192 unsigned last = nblocks - map_offset;
193
194 for (relative_block = 0; ; relative_block++) {
195 if (relative_block == last) {
196 clear_buffer_mapped(map_bh);
197 break;
198 }
199 if (page_block == blocks_per_page)
200 break;
201 blocks[page_block] = map_bh->b_blocknr + map_offset +
202 relative_block;
203 page_block++;
204 block_in_file++;
205 }
206 bdev = map_bh->b_bdev;
207 }
208
209 /*
210 * Then do more get_blocks calls until we are done with this page.
211 */
212 map_bh->b_page = page;
213 while (page_block < blocks_per_page) {
214 map_bh->b_state = 0;
215 map_bh->b_size = 0;
216
217 if (block_in_file < last_block) {
218 map_bh->b_size = (last_block-block_in_file) << blkbits;
219 if (get_block(inode, block_in_file, map_bh, 0))
220 goto confused;
221 *first_logical_block = block_in_file;
222 }
223
224 if (!buffer_mapped(map_bh)) {
225 fully_mapped = 0;
226 if (first_hole == blocks_per_page)
227 first_hole = page_block;
228 page_block++;
229 block_in_file++;
230 continue;
231 }
232
233 /* some filesystems will copy data into the page during
234 * the get_block call, in which case we don't want to
235 * read it again. map_buffer_to_page copies the data
236 * we just collected from get_block into the page's buffers
237 * so readpage doesn't have to repeat the get_block call
238 */
239 if (buffer_uptodate(map_bh)) {
240 map_buffer_to_page(page, map_bh, page_block);
241 goto confused;
242 }
243
244 if (first_hole != blocks_per_page)
245 goto confused; /* hole -> non-hole */
246
247 /* Contiguous blocks? */
248 if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
249 goto confused;
250 nblocks = map_bh->b_size >> blkbits;
251 for (relative_block = 0; ; relative_block++) {
252 if (relative_block == nblocks) {
253 clear_buffer_mapped(map_bh);
254 break;
255 } else if (page_block == blocks_per_page)
256 break;
257 blocks[page_block] = map_bh->b_blocknr+relative_block;
258 page_block++;
259 block_in_file++;
260 }
261 bdev = map_bh->b_bdev;
262 }
263
264 if (first_hole != blocks_per_page) {
265 zero_user_segment(page, first_hole << blkbits, PAGE_CACHE_SIZE);
266 if (first_hole == 0) {
267 SetPageUptodate(page);
268 unlock_page(page);
269 goto out;
270 }
271 } else if (fully_mapped) {
272 SetPageMappedToDisk(page);
273 }
274
275 if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) &&
276 cleancache_get_page(page) == 0) {
277 SetPageUptodate(page);
278 goto confused;
279 }
280
281 /*
282 * This page will go to BIO. Do we need to send this BIO off first?
283 */
284 if (bio && (*last_block_in_bio != blocks[0] - 1))
285 bio = mpage_bio_submit(READ, bio);
286
287alloc_new:
288 if (bio == NULL) {
289 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
290 min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
291 GFP_KERNEL);
292 if (bio == NULL)
293 goto confused;
294 }
295
296 length = first_hole << blkbits;
297 if (bio_add_page(bio, page, length, 0) < length) {
298 bio = mpage_bio_submit(READ, bio);
299 goto alloc_new;
300 }
301
302 relative_block = block_in_file - *first_logical_block;
303 nblocks = map_bh->b_size >> blkbits;
304 if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
305 (first_hole != blocks_per_page))
306 bio = mpage_bio_submit(READ, bio);
307 else
308 *last_block_in_bio = blocks[blocks_per_page - 1];
309out:
310 return bio;
311
312confused:
313 if (bio)
314 bio = mpage_bio_submit(READ, bio);
315 if (!PageUptodate(page))
316 block_read_full_page(page, get_block);
317 else
318 unlock_page(page);
319 goto out;
320}
321
322/**
323 * mpage_readpages - populate an address space with some pages & start reads against them
324 * @mapping: the address_space
325 * @pages: The address of a list_head which contains the target pages. These
326 * pages have their ->index populated and are otherwise uninitialised.
327 * The page at @pages->prev has the lowest file offset, and reads should be
328 * issued in @pages->prev to @pages->next order.
329 * @nr_pages: The number of pages at *@pages
330 * @get_block: The filesystem's block mapper function.
331 *
332 * This function walks the pages and the blocks within each page, building and
333 * emitting large BIOs.
334 *
335 * If anything unusual happens, such as:
336 *
337 * - encountering a page which has buffers
338 * - encountering a page which has a non-hole after a hole
339 * - encountering a page with non-contiguous blocks
340 *
341 * then this code just gives up and calls the buffer_head-based read function.
342 * It does handle a page which has holes at the end - that is a common case:
343 * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
344 *
345 * BH_Boundary explanation:
346 *
347 * There is a problem. The mpage read code assembles several pages, gets all
348 * their disk mappings, and then submits them all. That's fine, but obtaining
349 * the disk mappings may require I/O. Reads of indirect blocks, for example.
350 *
351 * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
352 * submitted in the following order:
353 * 12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
354 *
355 * because the indirect block has to be read to get the mappings of blocks
356 * 13,14,15,16. Obviously, this impacts performance.
357 *
358 * So what we do it to allow the filesystem's get_block() function to set
359 * BH_Boundary when it maps block 11. BH_Boundary says: mapping of the block
360 * after this one will require I/O against a block which is probably close to
361 * this one. So you should push what I/O you have currently accumulated.
362 *
363 * This all causes the disk requests to be issued in the correct order.
364 */
365int
366mpage_readpages(struct address_space *mapping, struct list_head *pages,
367 unsigned nr_pages, get_block_t get_block)
368{
369 struct bio *bio = NULL;
370 unsigned page_idx;
371 sector_t last_block_in_bio = 0;
372 struct buffer_head map_bh;
373 unsigned long first_logical_block = 0;
374 struct blk_plug plug;
375
376 blk_start_plug(&plug);
377
378 map_bh.b_state = 0;
379 map_bh.b_size = 0;
380 for (page_idx = 0; page_idx < nr_pages; page_idx++) {
381 struct page *page = list_entry(pages->prev, struct page, lru);
382
383 prefetchw(&page->flags);
384 list_del(&page->lru);
385 if (!add_to_page_cache_lru(page, mapping,
386 page->index, GFP_KERNEL)) {
387 bio = do_mpage_readpage(bio, page,
388 nr_pages - page_idx,
389 &last_block_in_bio, &map_bh,
390 &first_logical_block,
391 get_block);
392 }
393 page_cache_release(page);
394 }
395 BUG_ON(!list_empty(pages));
396 if (bio)
397 mpage_bio_submit(READ, bio);
398 blk_finish_plug(&plug);
399 return 0;
400}
401EXPORT_SYMBOL(mpage_readpages);
402
403/*
404 * This isn't called much at all
405 */
406int mpage_readpage(struct page *page, get_block_t get_block)
407{
408 struct bio *bio = NULL;
409 sector_t last_block_in_bio = 0;
410 struct buffer_head map_bh;
411 unsigned long first_logical_block = 0;
412
413 map_bh.b_state = 0;
414 map_bh.b_size = 0;
415 bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
416 &map_bh, &first_logical_block, get_block);
417 if (bio)
418 mpage_bio_submit(READ, bio);
419 return 0;
420}
421EXPORT_SYMBOL(mpage_readpage);
422
423/*
424 * Writing is not so simple.
425 *
426 * If the page has buffers then they will be used for obtaining the disk
427 * mapping. We only support pages which are fully mapped-and-dirty, with a
428 * special case for pages which are unmapped at the end: end-of-file.
429 *
430 * If the page has no buffers (preferred) then the page is mapped here.
431 *
432 * If all blocks are found to be contiguous then the page can go into the
433 * BIO. Otherwise fall back to the mapping's writepage().
434 *
435 * FIXME: This code wants an estimate of how many pages are still to be
436 * written, so it can intelligently allocate a suitably-sized BIO. For now,
437 * just allocate full-size (16-page) BIOs.
438 */
439
440struct mpage_data {
441 struct bio *bio;
442 sector_t last_block_in_bio;
443 get_block_t *get_block;
444 unsigned use_writepage;
445};
446
447static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
448 void *data)
449{
450 struct mpage_data *mpd = data;
451 struct bio *bio = mpd->bio;
452 struct address_space *mapping = page->mapping;
453 struct inode *inode = page->mapping->host;
454 const unsigned blkbits = inode->i_blkbits;
455 unsigned long end_index;
456 const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
457 sector_t last_block;
458 sector_t block_in_file;
459 sector_t blocks[MAX_BUF_PER_PAGE];
460 unsigned page_block;
461 unsigned first_unmapped = blocks_per_page;
462 struct block_device *bdev = NULL;
463 int boundary = 0;
464 sector_t boundary_block = 0;
465 struct block_device *boundary_bdev = NULL;
466 int length;
467 struct buffer_head map_bh;
468 loff_t i_size = i_size_read(inode);
469 int ret = 0;
470
471 if (page_has_buffers(page)) {
472 struct buffer_head *head = page_buffers(page);
473 struct buffer_head *bh = head;
474
475 /* If they're all mapped and dirty, do it */
476 page_block = 0;
477 do {
478 BUG_ON(buffer_locked(bh));
479 if (!buffer_mapped(bh)) {
480 /*
481 * unmapped dirty buffers are created by
482 * __set_page_dirty_buffers -> mmapped data
483 */
484 if (buffer_dirty(bh))
485 goto confused;
486 if (first_unmapped == blocks_per_page)
487 first_unmapped = page_block;
488 continue;
489 }
490
491 if (first_unmapped != blocks_per_page)
492 goto confused; /* hole -> non-hole */
493
494 if (!buffer_dirty(bh) || !buffer_uptodate(bh))
495 goto confused;
496 if (page_block) {
497 if (bh->b_blocknr != blocks[page_block-1] + 1)
498 goto confused;
499 }
500 blocks[page_block++] = bh->b_blocknr;
501 boundary = buffer_boundary(bh);
502 if (boundary) {
503 boundary_block = bh->b_blocknr;
504 boundary_bdev = bh->b_bdev;
505 }
506 bdev = bh->b_bdev;
507 } while ((bh = bh->b_this_page) != head);
508
509 if (first_unmapped)
510 goto page_is_mapped;
511
512 /*
513 * Page has buffers, but they are all unmapped. The page was
514 * created by pagein or read over a hole which was handled by
515 * block_read_full_page(). If this address_space is also
516 * using mpage_readpages then this can rarely happen.
517 */
518 goto confused;
519 }
520
521 /*
522 * The page has no buffers: map it to disk
523 */
524 BUG_ON(!PageUptodate(page));
525 block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
526 last_block = (i_size - 1) >> blkbits;
527 map_bh.b_page = page;
528 for (page_block = 0; page_block < blocks_per_page; ) {
529
530 map_bh.b_state = 0;
531 map_bh.b_size = 1 << blkbits;
532 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
533 goto confused;
534 if (buffer_new(&map_bh))
535 unmap_underlying_metadata(map_bh.b_bdev,
536 map_bh.b_blocknr);
537 if (buffer_boundary(&map_bh)) {
538 boundary_block = map_bh.b_blocknr;
539 boundary_bdev = map_bh.b_bdev;
540 }
541 if (page_block) {
542 if (map_bh.b_blocknr != blocks[page_block-1] + 1)
543 goto confused;
544 }
545 blocks[page_block++] = map_bh.b_blocknr;
546 boundary = buffer_boundary(&map_bh);
547 bdev = map_bh.b_bdev;
548 if (block_in_file == last_block)
549 break;
550 block_in_file++;
551 }
552 BUG_ON(page_block == 0);
553
554 first_unmapped = page_block;
555
556page_is_mapped:
557 end_index = i_size >> PAGE_CACHE_SHIFT;
558 if (page->index >= end_index) {
559 /*
560 * The page straddles i_size. It must be zeroed out on each
561 * and every writepage invocation because it may be mmapped.
562 * "A file is mapped in multiples of the page size. For a file
563 * that is not a multiple of the page size, the remaining memory
564 * is zeroed when mapped, and writes to that region are not
565 * written out to the file."
566 */
567 unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
568
569 if (page->index > end_index || !offset)
570 goto confused;
571 zero_user_segment(page, offset, PAGE_CACHE_SIZE);
572 }
573
574 /*
575 * This page will go to BIO. Do we need to send this BIO off first?
576 */
577 if (bio && mpd->last_block_in_bio != blocks[0] - 1)
578 bio = mpage_bio_submit(WRITE, bio);
579
580alloc_new:
581 if (bio == NULL) {
582 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
583 bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
584 if (bio == NULL)
585 goto confused;
586 }
587
588 /*
589 * Must try to add the page before marking the buffer clean or
590 * the confused fail path above (OOM) will be very confused when
591 * it finds all bh marked clean (i.e. it will not write anything)
592 */
593 length = first_unmapped << blkbits;
594 if (bio_add_page(bio, page, length, 0) < length) {
595 bio = mpage_bio_submit(WRITE, bio);
596 goto alloc_new;
597 }
598
599 /*
600 * OK, we have our BIO, so we can now mark the buffers clean. Make
601 * sure to only clean buffers which we know we'll be writing.
602 */
603 if (page_has_buffers(page)) {
604 struct buffer_head *head = page_buffers(page);
605 struct buffer_head *bh = head;
606 unsigned buffer_counter = 0;
607
608 do {
609 if (buffer_counter++ == first_unmapped)
610 break;
611 clear_buffer_dirty(bh);
612 bh = bh->b_this_page;
613 } while (bh != head);
614
615 /*
616 * we cannot drop the bh if the page is not uptodate
617 * or a concurrent readpage would fail to serialize with the bh
618 * and it would read from disk before we reach the platter.
619 */
620 if (buffer_heads_over_limit && PageUptodate(page))
621 try_to_free_buffers(page);
622 }
623
624 BUG_ON(PageWriteback(page));
625 set_page_writeback(page);
626 unlock_page(page);
627 if (boundary || (first_unmapped != blocks_per_page)) {
628 bio = mpage_bio_submit(WRITE, bio);
629 if (boundary_block) {
630 write_boundary_block(boundary_bdev,
631 boundary_block, 1 << blkbits);
632 }
633 } else {
634 mpd->last_block_in_bio = blocks[blocks_per_page - 1];
635 }
636 goto out;
637
638confused:
639 if (bio)
640 bio = mpage_bio_submit(WRITE, bio);
641
642 if (mpd->use_writepage) {
643 ret = mapping->a_ops->writepage(page, wbc);
644 } else {
645 ret = -EAGAIN;
646 goto out;
647 }
648 /*
649 * The caller has a ref on the inode, so *mapping is stable
650 */
651 mapping_set_error(mapping, ret);
652out:
653 mpd->bio = bio;
654 return ret;
655}
656
657/**
658 * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
659 * @mapping: address space structure to write
660 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
661 * @get_block: the filesystem's block mapper function.
662 * If this is NULL then use a_ops->writepage. Otherwise, go
663 * direct-to-BIO.
664 *
665 * This is a library function, which implements the writepages()
666 * address_space_operation.
667 *
668 * If a page is already under I/O, generic_writepages() skips it, even
669 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
670 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
671 * and msync() need to guarantee that all the data which was dirty at the time
672 * the call was made get new I/O started against them. If wbc->sync_mode is
673 * WB_SYNC_ALL then we were called for data integrity and we must wait for
674 * existing IO to complete.
675 */
676int
677mpage_writepages(struct address_space *mapping,
678 struct writeback_control *wbc, get_block_t get_block)
679{
680 struct blk_plug plug;
681 int ret;
682
683 blk_start_plug(&plug);
684
685 if (!get_block)
686 ret = generic_writepages(mapping, wbc);
687 else {
688 struct mpage_data mpd = {
689 .bio = NULL,
690 .last_block_in_bio = 0,
691 .get_block = get_block,
692 .use_writepage = 1,
693 };
694
695 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
696 if (mpd.bio)
697 mpage_bio_submit(WRITE, mpd.bio);
698 }
699 blk_finish_plug(&plug);
700 return ret;
701}
702EXPORT_SYMBOL(mpage_writepages);
703
704int mpage_writepage(struct page *page, get_block_t get_block,
705 struct writeback_control *wbc)
706{
707 struct mpage_data mpd = {
708 .bio = NULL,
709 .last_block_in_bio = 0,
710 .get_block = get_block,
711 .use_writepage = 0,
712 };
713 int ret = __mpage_writepage(page, wbc, &mpd);
714 if (mpd.bio)
715 mpage_bio_submit(WRITE, mpd.bio);
716 return ret;
717}
718EXPORT_SYMBOL(mpage_writepage);