xref: /openbmc/linux/fs/mpage.c (revision d5cb9783536a41df9f9cba5b0a1d78047ed787f7)
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 int mpage_end_io_read(struct bio *bio, unsigned int bytes_done, 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 	if (bio->bi_size)
48 		return 1;
49 
50 	do {
51 		struct page *page = bvec->bv_page;
52 
53 		if (--bvec >= bio->bi_io_vec)
54 			prefetchw(&bvec->bv_page->flags);
55 
56 		if (uptodate) {
57 			SetPageUptodate(page);
58 		} else {
59 			ClearPageUptodate(page);
60 			SetPageError(page);
61 		}
62 		unlock_page(page);
63 	} while (bvec >= bio->bi_io_vec);
64 	bio_put(bio);
65 	return 0;
66 }
67 
68 static int mpage_end_io_write(struct bio *bio, unsigned int bytes_done, int err)
69 {
70 	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
71 	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
72 
73 	if (bio->bi_size)
74 		return 1;
75 
76 	do {
77 		struct page *page = bvec->bv_page;
78 
79 		if (--bvec >= bio->bi_io_vec)
80 			prefetchw(&bvec->bv_page->flags);
81 
82 		if (!uptodate){
83 			SetPageError(page);
84 			if (page->mapping)
85 				set_bit(AS_EIO, &page->mapping->flags);
86 		}
87 		end_page_writeback(page);
88 	} while (bvec >= bio->bi_io_vec);
89 	bio_put(bio);
90 	return 0;
91 }
92 
93 static struct bio *mpage_bio_submit(int rw, struct bio *bio)
94 {
95 	bio->bi_end_io = mpage_end_io_read;
96 	if (rw == WRITE)
97 		bio->bi_end_io = mpage_end_io_write;
98 	submit_bio(rw, bio);
99 	return NULL;
100 }
101 
102 static struct bio *
103 mpage_alloc(struct block_device *bdev,
104 		sector_t first_sector, int nr_vecs,
105 		gfp_t gfp_flags)
106 {
107 	struct bio *bio;
108 
109 	bio = bio_alloc(gfp_flags, nr_vecs);
110 
111 	if (bio == NULL && (current->flags & PF_MEMALLOC)) {
112 		while (!bio && (nr_vecs /= 2))
113 			bio = bio_alloc(gfp_flags, nr_vecs);
114 	}
115 
116 	if (bio) {
117 		bio->bi_bdev = bdev;
118 		bio->bi_sector = first_sector;
119 	}
120 	return bio;
121 }
122 
123 /*
124  * support function for mpage_readpages.  The fs supplied get_block might
125  * return an up to date buffer.  This is used to map that buffer into
126  * the page, which allows readpage to avoid triggering a duplicate call
127  * to get_block.
128  *
129  * The idea is to avoid adding buffers to pages that don't already have
130  * them.  So when the buffer is up to date and the page size == block size,
131  * this marks the page up to date instead of adding new buffers.
132  */
133 static void
134 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
135 {
136 	struct inode *inode = page->mapping->host;
137 	struct buffer_head *page_bh, *head;
138 	int block = 0;
139 
140 	if (!page_has_buffers(page)) {
141 		/*
142 		 * don't make any buffers if there is only one buffer on
143 		 * the page and the page just needs to be set up to date
144 		 */
145 		if (inode->i_blkbits == PAGE_CACHE_SHIFT &&
146 		    buffer_uptodate(bh)) {
147 			SetPageUptodate(page);
148 			return;
149 		}
150 		create_empty_buffers(page, 1 << inode->i_blkbits, 0);
151 	}
152 	head = page_buffers(page);
153 	page_bh = head;
154 	do {
155 		if (block == page_block) {
156 			page_bh->b_state = bh->b_state;
157 			page_bh->b_bdev = bh->b_bdev;
158 			page_bh->b_blocknr = bh->b_blocknr;
159 			break;
160 		}
161 		page_bh = page_bh->b_this_page;
162 		block++;
163 	} while (page_bh != head);
164 }
165 
166 static struct bio *
167 do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
168 			sector_t *last_block_in_bio, get_block_t get_block)
169 {
170 	struct inode *inode = page->mapping->host;
171 	const unsigned blkbits = inode->i_blkbits;
172 	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
173 	const unsigned blocksize = 1 << blkbits;
174 	sector_t block_in_file;
175 	sector_t last_block;
176 	sector_t blocks[MAX_BUF_PER_PAGE];
177 	unsigned page_block;
178 	unsigned first_hole = blocks_per_page;
179 	struct block_device *bdev = NULL;
180 	struct buffer_head bh;
181 	int length;
182 	int fully_mapped = 1;
183 
184 	if (page_has_buffers(page))
185 		goto confused;
186 
187 	block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits);
188 	last_block = (i_size_read(inode) + blocksize - 1) >> blkbits;
189 
190 	bh.b_page = page;
191 	for (page_block = 0; page_block < blocks_per_page;
192 				page_block++, block_in_file++) {
193 		bh.b_state = 0;
194 		if (block_in_file < last_block) {
195 			if (get_block(inode, block_in_file, &bh, 0))
196 				goto confused;
197 		}
198 
199 		if (!buffer_mapped(&bh)) {
200 			fully_mapped = 0;
201 			if (first_hole == blocks_per_page)
202 				first_hole = page_block;
203 			continue;
204 		}
205 
206 		/* some filesystems will copy data into the page during
207 		 * the get_block call, in which case we don't want to
208 		 * read it again.  map_buffer_to_page copies the data
209 		 * we just collected from get_block into the page's buffers
210 		 * so readpage doesn't have to repeat the get_block call
211 		 */
212 		if (buffer_uptodate(&bh)) {
213 			map_buffer_to_page(page, &bh, page_block);
214 			goto confused;
215 		}
216 
217 		if (first_hole != blocks_per_page)
218 			goto confused;		/* hole -> non-hole */
219 
220 		/* Contiguous blocks? */
221 		if (page_block && blocks[page_block-1] != bh.b_blocknr-1)
222 			goto confused;
223 		blocks[page_block] = bh.b_blocknr;
224 		bdev = bh.b_bdev;
225 	}
226 
227 	if (first_hole != blocks_per_page) {
228 		char *kaddr = kmap_atomic(page, KM_USER0);
229 		memset(kaddr + (first_hole << blkbits), 0,
230 				PAGE_CACHE_SIZE - (first_hole << blkbits));
231 		flush_dcache_page(page);
232 		kunmap_atomic(kaddr, KM_USER0);
233 		if (first_hole == 0) {
234 			SetPageUptodate(page);
235 			unlock_page(page);
236 			goto out;
237 		}
238 	} else if (fully_mapped) {
239 		SetPageMappedToDisk(page);
240 	}
241 
242 	/*
243 	 * This page will go to BIO.  Do we need to send this BIO off first?
244 	 */
245 	if (bio && (*last_block_in_bio != blocks[0] - 1))
246 		bio = mpage_bio_submit(READ, bio);
247 
248 alloc_new:
249 	if (bio == NULL) {
250 		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
251 			  	min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
252 				GFP_KERNEL);
253 		if (bio == NULL)
254 			goto confused;
255 	}
256 
257 	length = first_hole << blkbits;
258 	if (bio_add_page(bio, page, length, 0) < length) {
259 		bio = mpage_bio_submit(READ, bio);
260 		goto alloc_new;
261 	}
262 
263 	if (buffer_boundary(&bh) || (first_hole != blocks_per_page))
264 		bio = mpage_bio_submit(READ, bio);
265 	else
266 		*last_block_in_bio = blocks[blocks_per_page - 1];
267 out:
268 	return bio;
269 
270 confused:
271 	if (bio)
272 		bio = mpage_bio_submit(READ, bio);
273 	if (!PageUptodate(page))
274 	        block_read_full_page(page, get_block);
275 	else
276 		unlock_page(page);
277 	goto out;
278 }
279 
280 /**
281  * mpage_readpages - populate an address space with some pages, and
282  *                       start reads against them.
283  *
284  * @mapping: the address_space
285  * @pages: The address of a list_head which contains the target pages.  These
286  *   pages have their ->index populated and are otherwise uninitialised.
287  *
288  *   The page at @pages->prev has the lowest file offset, and reads should be
289  *   issued in @pages->prev to @pages->next order.
290  *
291  * @nr_pages: The number of pages at *@pages
292  * @get_block: The filesystem's block mapper function.
293  *
294  * This function walks the pages and the blocks within each page, building and
295  * emitting large BIOs.
296  *
297  * If anything unusual happens, such as:
298  *
299  * - encountering a page which has buffers
300  * - encountering a page which has a non-hole after a hole
301  * - encountering a page with non-contiguous blocks
302  *
303  * then this code just gives up and calls the buffer_head-based read function.
304  * It does handle a page which has holes at the end - that is a common case:
305  * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
306  *
307  * BH_Boundary explanation:
308  *
309  * There is a problem.  The mpage read code assembles several pages, gets all
310  * their disk mappings, and then submits them all.  That's fine, but obtaining
311  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
312  *
313  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
314  * submitted in the following order:
315  * 	12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
316  * because the indirect block has to be read to get the mappings of blocks
317  * 13,14,15,16.  Obviously, this impacts performance.
318  *
319  * So what we do it to allow the filesystem's get_block() function to set
320  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
321  * after this one will require I/O against a block which is probably close to
322  * this one.  So you should push what I/O you have currently accumulated.
323  *
324  * This all causes the disk requests to be issued in the correct order.
325  */
326 int
327 mpage_readpages(struct address_space *mapping, struct list_head *pages,
328 				unsigned nr_pages, get_block_t get_block)
329 {
330 	struct bio *bio = NULL;
331 	unsigned page_idx;
332 	sector_t last_block_in_bio = 0;
333 	struct pagevec lru_pvec;
334 
335 	pagevec_init(&lru_pvec, 0);
336 	for (page_idx = 0; page_idx < nr_pages; page_idx++) {
337 		struct page *page = list_entry(pages->prev, struct page, lru);
338 
339 		prefetchw(&page->flags);
340 		list_del(&page->lru);
341 		if (!add_to_page_cache(page, mapping,
342 					page->index, GFP_KERNEL)) {
343 			bio = do_mpage_readpage(bio, page,
344 					nr_pages - page_idx,
345 					&last_block_in_bio, get_block);
346 			if (!pagevec_add(&lru_pvec, page))
347 				__pagevec_lru_add(&lru_pvec);
348 		} else {
349 			page_cache_release(page);
350 		}
351 	}
352 	pagevec_lru_add(&lru_pvec);
353 	BUG_ON(!list_empty(pages));
354 	if (bio)
355 		mpage_bio_submit(READ, bio);
356 	return 0;
357 }
358 EXPORT_SYMBOL(mpage_readpages);
359 
360 /*
361  * This isn't called much at all
362  */
363 int mpage_readpage(struct page *page, get_block_t get_block)
364 {
365 	struct bio *bio = NULL;
366 	sector_t last_block_in_bio = 0;
367 
368 	bio = do_mpage_readpage(bio, page, 1,
369 			&last_block_in_bio, get_block);
370 	if (bio)
371 		mpage_bio_submit(READ, bio);
372 	return 0;
373 }
374 EXPORT_SYMBOL(mpage_readpage);
375 
376 /*
377  * Writing is not so simple.
378  *
379  * If the page has buffers then they will be used for obtaining the disk
380  * mapping.  We only support pages which are fully mapped-and-dirty, with a
381  * special case for pages which are unmapped at the end: end-of-file.
382  *
383  * If the page has no buffers (preferred) then the page is mapped here.
384  *
385  * If all blocks are found to be contiguous then the page can go into the
386  * BIO.  Otherwise fall back to the mapping's writepage().
387  *
388  * FIXME: This code wants an estimate of how many pages are still to be
389  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
390  * just allocate full-size (16-page) BIOs.
391  */
392 static struct bio *
393 __mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
394 	sector_t *last_block_in_bio, int *ret, struct writeback_control *wbc,
395 	writepage_t writepage_fn)
396 {
397 	struct address_space *mapping = page->mapping;
398 	struct inode *inode = page->mapping->host;
399 	const unsigned blkbits = inode->i_blkbits;
400 	unsigned long end_index;
401 	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
402 	sector_t last_block;
403 	sector_t block_in_file;
404 	sector_t blocks[MAX_BUF_PER_PAGE];
405 	unsigned page_block;
406 	unsigned first_unmapped = blocks_per_page;
407 	struct block_device *bdev = NULL;
408 	int boundary = 0;
409 	sector_t boundary_block = 0;
410 	struct block_device *boundary_bdev = NULL;
411 	int length;
412 	struct buffer_head map_bh;
413 	loff_t i_size = i_size_read(inode);
414 
415 	if (page_has_buffers(page)) {
416 		struct buffer_head *head = page_buffers(page);
417 		struct buffer_head *bh = head;
418 
419 		/* If they're all mapped and dirty, do it */
420 		page_block = 0;
421 		do {
422 			BUG_ON(buffer_locked(bh));
423 			if (!buffer_mapped(bh)) {
424 				/*
425 				 * unmapped dirty buffers are created by
426 				 * __set_page_dirty_buffers -> mmapped data
427 				 */
428 				if (buffer_dirty(bh))
429 					goto confused;
430 				if (first_unmapped == blocks_per_page)
431 					first_unmapped = page_block;
432 				continue;
433 			}
434 
435 			if (first_unmapped != blocks_per_page)
436 				goto confused;	/* hole -> non-hole */
437 
438 			if (!buffer_dirty(bh) || !buffer_uptodate(bh))
439 				goto confused;
440 			if (page_block) {
441 				if (bh->b_blocknr != blocks[page_block-1] + 1)
442 					goto confused;
443 			}
444 			blocks[page_block++] = bh->b_blocknr;
445 			boundary = buffer_boundary(bh);
446 			if (boundary) {
447 				boundary_block = bh->b_blocknr;
448 				boundary_bdev = bh->b_bdev;
449 			}
450 			bdev = bh->b_bdev;
451 		} while ((bh = bh->b_this_page) != head);
452 
453 		if (first_unmapped)
454 			goto page_is_mapped;
455 
456 		/*
457 		 * Page has buffers, but they are all unmapped. The page was
458 		 * created by pagein or read over a hole which was handled by
459 		 * block_read_full_page().  If this address_space is also
460 		 * using mpage_readpages then this can rarely happen.
461 		 */
462 		goto confused;
463 	}
464 
465 	/*
466 	 * The page has no buffers: map it to disk
467 	 */
468 	BUG_ON(!PageUptodate(page));
469 	block_in_file = page->index << (PAGE_CACHE_SHIFT - blkbits);
470 	last_block = (i_size - 1) >> blkbits;
471 	map_bh.b_page = page;
472 	for (page_block = 0; page_block < blocks_per_page; ) {
473 
474 		map_bh.b_state = 0;
475 		if (get_block(inode, block_in_file, &map_bh, 1))
476 			goto confused;
477 		if (buffer_new(&map_bh))
478 			unmap_underlying_metadata(map_bh.b_bdev,
479 						map_bh.b_blocknr);
480 		if (buffer_boundary(&map_bh)) {
481 			boundary_block = map_bh.b_blocknr;
482 			boundary_bdev = map_bh.b_bdev;
483 		}
484 		if (page_block) {
485 			if (map_bh.b_blocknr != blocks[page_block-1] + 1)
486 				goto confused;
487 		}
488 		blocks[page_block++] = map_bh.b_blocknr;
489 		boundary = buffer_boundary(&map_bh);
490 		bdev = map_bh.b_bdev;
491 		if (block_in_file == last_block)
492 			break;
493 		block_in_file++;
494 	}
495 	BUG_ON(page_block == 0);
496 
497 	first_unmapped = page_block;
498 
499 page_is_mapped:
500 	end_index = i_size >> PAGE_CACHE_SHIFT;
501 	if (page->index >= end_index) {
502 		/*
503 		 * The page straddles i_size.  It must be zeroed out on each
504 		 * and every writepage invokation because it may be mmapped.
505 		 * "A file is mapped in multiples of the page size.  For a file
506 		 * that is not a multiple of the page size, the remaining memory
507 		 * is zeroed when mapped, and writes to that region are not
508 		 * written out to the file."
509 		 */
510 		unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
511 		char *kaddr;
512 
513 		if (page->index > end_index || !offset)
514 			goto confused;
515 		kaddr = kmap_atomic(page, KM_USER0);
516 		memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
517 		flush_dcache_page(page);
518 		kunmap_atomic(kaddr, KM_USER0);
519 	}
520 
521 	/*
522 	 * This page will go to BIO.  Do we need to send this BIO off first?
523 	 */
524 	if (bio && *last_block_in_bio != blocks[0] - 1)
525 		bio = mpage_bio_submit(WRITE, bio);
526 
527 alloc_new:
528 	if (bio == NULL) {
529 		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
530 				bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
531 		if (bio == NULL)
532 			goto confused;
533 	}
534 
535 	/*
536 	 * Must try to add the page before marking the buffer clean or
537 	 * the confused fail path above (OOM) will be very confused when
538 	 * it finds all bh marked clean (i.e. it will not write anything)
539 	 */
540 	length = first_unmapped << blkbits;
541 	if (bio_add_page(bio, page, length, 0) < length) {
542 		bio = mpage_bio_submit(WRITE, bio);
543 		goto alloc_new;
544 	}
545 
546 	/*
547 	 * OK, we have our BIO, so we can now mark the buffers clean.  Make
548 	 * sure to only clean buffers which we know we'll be writing.
549 	 */
550 	if (page_has_buffers(page)) {
551 		struct buffer_head *head = page_buffers(page);
552 		struct buffer_head *bh = head;
553 		unsigned buffer_counter = 0;
554 
555 		do {
556 			if (buffer_counter++ == first_unmapped)
557 				break;
558 			clear_buffer_dirty(bh);
559 			bh = bh->b_this_page;
560 		} while (bh != head);
561 
562 		/*
563 		 * we cannot drop the bh if the page is not uptodate
564 		 * or a concurrent readpage would fail to serialize with the bh
565 		 * and it would read from disk before we reach the platter.
566 		 */
567 		if (buffer_heads_over_limit && PageUptodate(page))
568 			try_to_free_buffers(page);
569 	}
570 
571 	BUG_ON(PageWriteback(page));
572 	set_page_writeback(page);
573 	unlock_page(page);
574 	if (boundary || (first_unmapped != blocks_per_page)) {
575 		bio = mpage_bio_submit(WRITE, bio);
576 		if (boundary_block) {
577 			write_boundary_block(boundary_bdev,
578 					boundary_block, 1 << blkbits);
579 		}
580 	} else {
581 		*last_block_in_bio = blocks[blocks_per_page - 1];
582 	}
583 	goto out;
584 
585 confused:
586 	if (bio)
587 		bio = mpage_bio_submit(WRITE, bio);
588 
589 	if (writepage_fn) {
590 		*ret = (*writepage_fn)(page, wbc);
591 	} else {
592 		*ret = -EAGAIN;
593 		goto out;
594 	}
595 	/*
596 	 * The caller has a ref on the inode, so *mapping is stable
597 	 */
598 	if (*ret) {
599 		if (*ret == -ENOSPC)
600 			set_bit(AS_ENOSPC, &mapping->flags);
601 		else
602 			set_bit(AS_EIO, &mapping->flags);
603 	}
604 out:
605 	return bio;
606 }
607 
608 /**
609  * mpage_writepages - walk the list of dirty pages of the given
610  * address space and writepage() all of them.
611  *
612  * @mapping: address space structure to write
613  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
614  * @get_block: the filesystem's block mapper function.
615  *             If this is NULL then use a_ops->writepage.  Otherwise, go
616  *             direct-to-BIO.
617  *
618  * This is a library function, which implements the writepages()
619  * address_space_operation.
620  *
621  * If a page is already under I/O, generic_writepages() skips it, even
622  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
623  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
624  * and msync() need to guarantee that all the data which was dirty at the time
625  * the call was made get new I/O started against them.  If wbc->sync_mode is
626  * WB_SYNC_ALL then we were called for data integrity and we must wait for
627  * existing IO to complete.
628  */
629 int
630 mpage_writepages(struct address_space *mapping,
631 		struct writeback_control *wbc, get_block_t get_block)
632 {
633 	struct backing_dev_info *bdi = mapping->backing_dev_info;
634 	struct bio *bio = NULL;
635 	sector_t last_block_in_bio = 0;
636 	int ret = 0;
637 	int done = 0;
638 	int (*writepage)(struct page *page, struct writeback_control *wbc);
639 	struct pagevec pvec;
640 	int nr_pages;
641 	pgoff_t index;
642 	pgoff_t end = -1;		/* Inclusive */
643 	int scanned = 0;
644 	int is_range = 0;
645 
646 	if (wbc->nonblocking && bdi_write_congested(bdi)) {
647 		wbc->encountered_congestion = 1;
648 		return 0;
649 	}
650 
651 	writepage = NULL;
652 	if (get_block == NULL)
653 		writepage = mapping->a_ops->writepage;
654 
655 	pagevec_init(&pvec, 0);
656 	if (wbc->sync_mode == WB_SYNC_NONE) {
657 		index = mapping->writeback_index; /* Start from prev offset */
658 	} else {
659 		index = 0;			  /* whole-file sweep */
660 		scanned = 1;
661 	}
662 	if (wbc->start || wbc->end) {
663 		index = wbc->start >> PAGE_CACHE_SHIFT;
664 		end = wbc->end >> PAGE_CACHE_SHIFT;
665 		is_range = 1;
666 		scanned = 1;
667 	}
668 retry:
669 	while (!done && (index <= end) &&
670 			(nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
671 			PAGECACHE_TAG_DIRTY,
672 			min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
673 		unsigned i;
674 
675 		scanned = 1;
676 		for (i = 0; i < nr_pages; i++) {
677 			struct page *page = pvec.pages[i];
678 
679 			/*
680 			 * At this point we hold neither mapping->tree_lock nor
681 			 * lock on the page itself: the page may be truncated or
682 			 * invalidated (changing page->mapping to NULL), or even
683 			 * swizzled back from swapper_space to tmpfs file
684 			 * mapping
685 			 */
686 
687 			lock_page(page);
688 
689 			if (unlikely(page->mapping != mapping)) {
690 				unlock_page(page);
691 				continue;
692 			}
693 
694 			if (unlikely(is_range) && page->index > end) {
695 				done = 1;
696 				unlock_page(page);
697 				continue;
698 			}
699 
700 			if (wbc->sync_mode != WB_SYNC_NONE)
701 				wait_on_page_writeback(page);
702 
703 			if (PageWriteback(page) ||
704 					!clear_page_dirty_for_io(page)) {
705 				unlock_page(page);
706 				continue;
707 			}
708 
709 			if (writepage) {
710 				ret = (*writepage)(page, wbc);
711 				if (ret) {
712 					if (ret == -ENOSPC)
713 						set_bit(AS_ENOSPC,
714 							&mapping->flags);
715 					else
716 						set_bit(AS_EIO,
717 							&mapping->flags);
718 				}
719 			} else {
720 				bio = __mpage_writepage(bio, page, get_block,
721 						&last_block_in_bio, &ret, wbc,
722 						page->mapping->a_ops->writepage);
723 			}
724 			if (unlikely(ret == WRITEPAGE_ACTIVATE))
725 				unlock_page(page);
726 			if (ret || (--(wbc->nr_to_write) <= 0))
727 				done = 1;
728 			if (wbc->nonblocking && bdi_write_congested(bdi)) {
729 				wbc->encountered_congestion = 1;
730 				done = 1;
731 			}
732 		}
733 		pagevec_release(&pvec);
734 		cond_resched();
735 	}
736 	if (!scanned && !done) {
737 		/*
738 		 * We hit the last page and there is more work to be done: wrap
739 		 * back to the start of the file
740 		 */
741 		scanned = 1;
742 		index = 0;
743 		goto retry;
744 	}
745 	if (!is_range)
746 		mapping->writeback_index = index;
747 	if (bio)
748 		mpage_bio_submit(WRITE, bio);
749 	return ret;
750 }
751 EXPORT_SYMBOL(mpage_writepages);
752 
753 int mpage_writepage(struct page *page, get_block_t get_block,
754 	struct writeback_control *wbc)
755 {
756 	int ret = 0;
757 	struct bio *bio;
758 	sector_t last_block_in_bio = 0;
759 
760 	bio = __mpage_writepage(NULL, page, get_block,
761 			&last_block_in_bio, &ret, wbc, NULL);
762 	if (bio)
763 		mpage_bio_submit(WRITE, bio);
764 
765 	return ret;
766 }
767 EXPORT_SYMBOL(mpage_writepage);
768