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