timerfd: support CLOCK_BOOTTIME clock
[linux-3.10.git] / fs / mpage.c
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/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  */
44 static 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
74 static 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
81 static struct bio *
82 mpage_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  */
112 static void 
113 map_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  */
154 static struct bio *
155 do_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
287 alloc_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];
309 out:
310         return bio;
311
312 confused:
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  */
365 int
366 mpage_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
375         map_bh.b_state = 0;
376         map_bh.b_size = 0;
377         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
378                 struct page *page = list_entry(pages->prev, struct page, lru);
379
380                 prefetchw(&page->flags);
381                 list_del(&page->lru);
382                 if (!add_to_page_cache_lru(page, mapping,
383                                         page->index, GFP_KERNEL)) {
384                         bio = do_mpage_readpage(bio, page,
385                                         nr_pages - page_idx,
386                                         &last_block_in_bio, &map_bh,
387                                         &first_logical_block,
388                                         get_block);
389                 }
390                 page_cache_release(page);
391         }
392         BUG_ON(!list_empty(pages));
393         if (bio)
394                 mpage_bio_submit(READ, bio);
395         return 0;
396 }
397 EXPORT_SYMBOL(mpage_readpages);
398
399 /*
400  * This isn't called much at all
401  */
402 int mpage_readpage(struct page *page, get_block_t get_block)
403 {
404         struct bio *bio = NULL;
405         sector_t last_block_in_bio = 0;
406         struct buffer_head map_bh;
407         unsigned long first_logical_block = 0;
408
409         map_bh.b_state = 0;
410         map_bh.b_size = 0;
411         bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
412                         &map_bh, &first_logical_block, get_block);
413         if (bio)
414                 mpage_bio_submit(READ, bio);
415         return 0;
416 }
417 EXPORT_SYMBOL(mpage_readpage);
418
419 /*
420  * Writing is not so simple.
421  *
422  * If the page has buffers then they will be used for obtaining the disk
423  * mapping.  We only support pages which are fully mapped-and-dirty, with a
424  * special case for pages which are unmapped at the end: end-of-file.
425  *
426  * If the page has no buffers (preferred) then the page is mapped here.
427  *
428  * If all blocks are found to be contiguous then the page can go into the
429  * BIO.  Otherwise fall back to the mapping's writepage().
430  * 
431  * FIXME: This code wants an estimate of how many pages are still to be
432  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
433  * just allocate full-size (16-page) BIOs.
434  */
435
436 struct mpage_data {
437         struct bio *bio;
438         sector_t last_block_in_bio;
439         get_block_t *get_block;
440         unsigned use_writepage;
441 };
442
443 static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
444                       void *data)
445 {
446         struct mpage_data *mpd = data;
447         struct bio *bio = mpd->bio;
448         struct address_space *mapping = page->mapping;
449         struct inode *inode = page->mapping->host;
450         const unsigned blkbits = inode->i_blkbits;
451         unsigned long end_index;
452         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
453         sector_t last_block;
454         sector_t block_in_file;
455         sector_t blocks[MAX_BUF_PER_PAGE];
456         unsigned page_block;
457         unsigned first_unmapped = blocks_per_page;
458         struct block_device *bdev = NULL;
459         int boundary = 0;
460         sector_t boundary_block = 0;
461         struct block_device *boundary_bdev = NULL;
462         int length;
463         struct buffer_head map_bh;
464         loff_t i_size = i_size_read(inode);
465         int ret = 0;
466
467         if (page_has_buffers(page)) {
468                 struct buffer_head *head = page_buffers(page);
469                 struct buffer_head *bh = head;
470
471                 /* If they're all mapped and dirty, do it */
472                 page_block = 0;
473                 do {
474                         BUG_ON(buffer_locked(bh));
475                         if (!buffer_mapped(bh)) {
476                                 /*
477                                  * unmapped dirty buffers are created by
478                                  * __set_page_dirty_buffers -> mmapped data
479                                  */
480                                 if (buffer_dirty(bh))
481                                         goto confused;
482                                 if (first_unmapped == blocks_per_page)
483                                         first_unmapped = page_block;
484                                 continue;
485                         }
486
487                         if (first_unmapped != blocks_per_page)
488                                 goto confused;  /* hole -> non-hole */
489
490                         if (!buffer_dirty(bh) || !buffer_uptodate(bh))
491                                 goto confused;
492                         if (page_block) {
493                                 if (bh->b_blocknr != blocks[page_block-1] + 1)
494                                         goto confused;
495                         }
496                         blocks[page_block++] = bh->b_blocknr;
497                         boundary = buffer_boundary(bh);
498                         if (boundary) {
499                                 boundary_block = bh->b_blocknr;
500                                 boundary_bdev = bh->b_bdev;
501                         }
502                         bdev = bh->b_bdev;
503                 } while ((bh = bh->b_this_page) != head);
504
505                 if (first_unmapped)
506                         goto page_is_mapped;
507
508                 /*
509                  * Page has buffers, but they are all unmapped. The page was
510                  * created by pagein or read over a hole which was handled by
511                  * block_read_full_page().  If this address_space is also
512                  * using mpage_readpages then this can rarely happen.
513                  */
514                 goto confused;
515         }
516
517         /*
518          * The page has no buffers: map it to disk
519          */
520         BUG_ON(!PageUptodate(page));
521         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
522         last_block = (i_size - 1) >> blkbits;
523         map_bh.b_page = page;
524         for (page_block = 0; page_block < blocks_per_page; ) {
525
526                 map_bh.b_state = 0;
527                 map_bh.b_size = 1 << blkbits;
528                 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
529                         goto confused;
530                 if (buffer_new(&map_bh))
531                         unmap_underlying_metadata(map_bh.b_bdev,
532                                                 map_bh.b_blocknr);
533                 if (buffer_boundary(&map_bh)) {
534                         boundary_block = map_bh.b_blocknr;
535                         boundary_bdev = map_bh.b_bdev;
536                 }
537                 if (page_block) {
538                         if (map_bh.b_blocknr != blocks[page_block-1] + 1)
539                                 goto confused;
540                 }
541                 blocks[page_block++] = map_bh.b_blocknr;
542                 boundary = buffer_boundary(&map_bh);
543                 bdev = map_bh.b_bdev;
544                 if (block_in_file == last_block)
545                         break;
546                 block_in_file++;
547         }
548         BUG_ON(page_block == 0);
549
550         first_unmapped = page_block;
551
552 page_is_mapped:
553         end_index = i_size >> PAGE_CACHE_SHIFT;
554         if (page->index >= end_index) {
555                 /*
556                  * The page straddles i_size.  It must be zeroed out on each
557                  * and every writepage invocation because it may be mmapped.
558                  * "A file is mapped in multiples of the page size.  For a file
559                  * that is not a multiple of the page size, the remaining memory
560                  * is zeroed when mapped, and writes to that region are not
561                  * written out to the file."
562                  */
563                 unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
564
565                 if (page->index > end_index || !offset)
566                         goto confused;
567                 zero_user_segment(page, offset, PAGE_CACHE_SIZE);
568         }
569
570         /*
571          * This page will go to BIO.  Do we need to send this BIO off first?
572          */
573         if (bio && mpd->last_block_in_bio != blocks[0] - 1)
574                 bio = mpage_bio_submit(WRITE, bio);
575
576 alloc_new:
577         if (bio == NULL) {
578                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
579                                 bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
580                 if (bio == NULL)
581                         goto confused;
582         }
583
584         /*
585          * Must try to add the page before marking the buffer clean or
586          * the confused fail path above (OOM) will be very confused when
587          * it finds all bh marked clean (i.e. it will not write anything)
588          */
589         length = first_unmapped << blkbits;
590         if (bio_add_page(bio, page, length, 0) < length) {
591                 bio = mpage_bio_submit(WRITE, bio);
592                 goto alloc_new;
593         }
594
595         /*
596          * OK, we have our BIO, so we can now mark the buffers clean.  Make
597          * sure to only clean buffers which we know we'll be writing.
598          */
599         if (page_has_buffers(page)) {
600                 struct buffer_head *head = page_buffers(page);
601                 struct buffer_head *bh = head;
602                 unsigned buffer_counter = 0;
603
604                 do {
605                         if (buffer_counter++ == first_unmapped)
606                                 break;
607                         clear_buffer_dirty(bh);
608                         bh = bh->b_this_page;
609                 } while (bh != head);
610
611                 /*
612                  * we cannot drop the bh if the page is not uptodate
613                  * or a concurrent readpage would fail to serialize with the bh
614                  * and it would read from disk before we reach the platter.
615                  */
616                 if (buffer_heads_over_limit && PageUptodate(page))
617                         try_to_free_buffers(page);
618         }
619
620         BUG_ON(PageWriteback(page));
621         set_page_writeback(page);
622         unlock_page(page);
623         if (boundary || (first_unmapped != blocks_per_page)) {
624                 bio = mpage_bio_submit(WRITE, bio);
625                 if (boundary_block) {
626                         write_boundary_block(boundary_bdev,
627                                         boundary_block, 1 << blkbits);
628                 }
629         } else {
630                 mpd->last_block_in_bio = blocks[blocks_per_page - 1];
631         }
632         goto out;
633
634 confused:
635         if (bio)
636                 bio = mpage_bio_submit(WRITE, bio);
637
638         if (mpd->use_writepage) {
639                 ret = mapping->a_ops->writepage(page, wbc);
640         } else {
641                 ret = -EAGAIN;
642                 goto out;
643         }
644         /*
645          * The caller has a ref on the inode, so *mapping is stable
646          */
647         mapping_set_error(mapping, ret);
648 out:
649         mpd->bio = bio;
650         return ret;
651 }
652
653 /**
654  * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
655  * @mapping: address space structure to write
656  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
657  * @get_block: the filesystem's block mapper function.
658  *             If this is NULL then use a_ops->writepage.  Otherwise, go
659  *             direct-to-BIO.
660  *
661  * This is a library function, which implements the writepages()
662  * address_space_operation.
663  *
664  * If a page is already under I/O, generic_writepages() skips it, even
665  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
666  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
667  * and msync() need to guarantee that all the data which was dirty at the time
668  * the call was made get new I/O started against them.  If wbc->sync_mode is
669  * WB_SYNC_ALL then we were called for data integrity and we must wait for
670  * existing IO to complete.
671  */
672 int
673 mpage_writepages(struct address_space *mapping,
674                 struct writeback_control *wbc, get_block_t get_block)
675 {
676         struct blk_plug plug;
677         int ret;
678
679         blk_start_plug(&plug);
680
681         if (!get_block)
682                 ret = generic_writepages(mapping, wbc);
683         else {
684                 struct mpage_data mpd = {
685                         .bio = NULL,
686                         .last_block_in_bio = 0,
687                         .get_block = get_block,
688                         .use_writepage = 1,
689                 };
690
691                 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
692                 if (mpd.bio)
693                         mpage_bio_submit(WRITE, mpd.bio);
694         }
695         blk_finish_plug(&plug);
696         return ret;
697 }
698 EXPORT_SYMBOL(mpage_writepages);
699
700 int mpage_writepage(struct page *page, get_block_t get_block,
701         struct writeback_control *wbc)
702 {
703         struct mpage_data mpd = {
704                 .bio = NULL,
705                 .last_block_in_bio = 0,
706                 .get_block = get_block,
707                 .use_writepage = 0,
708         };
709         int ret = __mpage_writepage(page, wbc, &mpd);
710         if (mpd.bio)
711                 mpage_bio_submit(WRITE, mpd.bio);
712         return ret;
713 }
714 EXPORT_SYMBOL(mpage_writepage);