xfs: optimize the negative xattr caching
[linux-2.6.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/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  */
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         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 }
401 EXPORT_SYMBOL(mpage_readpages);
402
403 /*
404  * This isn't called much at all
405  */
406 int 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 }
421 EXPORT_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
440 struct 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
447 static 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
556 page_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
580 alloc_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
638 confused:
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);
652 out:
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  */
676 int
677 mpage_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 }
702 EXPORT_SYMBOL(mpage_writepages);
703
704 int 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 }
718 EXPORT_SYMBOL(mpage_writepage);