xref: /openbmc/linux/fs/mpage.c (revision 173940b3)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * fs/mpage.c
4  *
5  * Copyright (C) 2002, Linus Torvalds.
6  *
7  * Contains functions related to preparing and submitting BIOs which contain
8  * multiple pagecache pages.
9  *
10  * 15May2002	Andrew Morton
11  *		Initial version
12  * 27Jun2002	axboe@suse.de
13  *		use bio_add_page() to build bio's just the right size
14  */
15 
16 #include <linux/kernel.h>
17 #include <linux/export.h>
18 #include <linux/mm.h>
19 #include <linux/kdev_t.h>
20 #include <linux/gfp.h>
21 #include <linux/bio.h>
22 #include <linux/fs.h>
23 #include <linux/buffer_head.h>
24 #include <linux/blkdev.h>
25 #include <linux/highmem.h>
26 #include <linux/prefetch.h>
27 #include <linux/mpage.h>
28 #include <linux/mm_inline.h>
29 #include <linux/writeback.h>
30 #include <linux/backing-dev.h>
31 #include <linux/pagevec.h>
32 #include "internal.h"
33 
34 /*
35  * I/O completion handler for multipage BIOs.
36  *
37  * The mpage code never puts partial pages into a BIO (except for end-of-file).
38  * If a page does not map to a contiguous run of blocks then it simply falls
39  * back to block_read_full_folio().
40  *
41  * Why is this?  If a page's completion depends on a number of different BIOs
42  * which can complete in any order (or at the same time) then determining the
43  * status of that page is hard.  See end_buffer_async_read() for the details.
44  * There is no point in duplicating all that complexity.
45  */
46 static void mpage_end_io(struct bio *bio)
47 {
48 	struct bio_vec *bv;
49 	struct bvec_iter_all iter_all;
50 
51 	bio_for_each_segment_all(bv, bio, iter_all) {
52 		struct page *page = bv->bv_page;
53 		page_endio(page, bio_op(bio),
54 			   blk_status_to_errno(bio->bi_status));
55 	}
56 
57 	bio_put(bio);
58 }
59 
60 static struct bio *mpage_bio_submit(struct bio *bio)
61 {
62 	bio->bi_end_io = mpage_end_io;
63 	guard_bio_eod(bio);
64 	submit_bio(bio);
65 	return NULL;
66 }
67 
68 /*
69  * support function for mpage_readahead.  The fs supplied get_block might
70  * return an up to date buffer.  This is used to map that buffer into
71  * the page, which allows read_folio to avoid triggering a duplicate call
72  * to get_block.
73  *
74  * The idea is to avoid adding buffers to pages that don't already have
75  * them.  So when the buffer is up to date and the page size == block size,
76  * this marks the page up to date instead of adding new buffers.
77  */
78 static void
79 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
80 {
81 	struct inode *inode = page->mapping->host;
82 	struct buffer_head *page_bh, *head;
83 	int block = 0;
84 
85 	if (!page_has_buffers(page)) {
86 		/*
87 		 * don't make any buffers if there is only one buffer on
88 		 * the page and the page just needs to be set up to date
89 		 */
90 		if (inode->i_blkbits == PAGE_SHIFT &&
91 		    buffer_uptodate(bh)) {
92 			SetPageUptodate(page);
93 			return;
94 		}
95 		create_empty_buffers(page, i_blocksize(inode), 0);
96 	}
97 	head = page_buffers(page);
98 	page_bh = head;
99 	do {
100 		if (block == page_block) {
101 			page_bh->b_state = bh->b_state;
102 			page_bh->b_bdev = bh->b_bdev;
103 			page_bh->b_blocknr = bh->b_blocknr;
104 			break;
105 		}
106 		page_bh = page_bh->b_this_page;
107 		block++;
108 	} while (page_bh != head);
109 }
110 
111 struct mpage_readpage_args {
112 	struct bio *bio;
113 	struct page *page;
114 	unsigned int nr_pages;
115 	bool is_readahead;
116 	sector_t last_block_in_bio;
117 	struct buffer_head map_bh;
118 	unsigned long first_logical_block;
119 	get_block_t *get_block;
120 };
121 
122 /*
123  * This is the worker routine which does all the work of mapping the disk
124  * blocks and constructs largest possible bios, submits them for IO if the
125  * blocks are not contiguous on the disk.
126  *
127  * We pass a buffer_head back and forth and use its buffer_mapped() flag to
128  * represent the validity of its disk mapping and to decide when to do the next
129  * get_block() call.
130  */
131 static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
132 {
133 	struct page *page = args->page;
134 	struct inode *inode = page->mapping->host;
135 	const unsigned blkbits = inode->i_blkbits;
136 	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
137 	const unsigned blocksize = 1 << blkbits;
138 	struct buffer_head *map_bh = &args->map_bh;
139 	sector_t block_in_file;
140 	sector_t last_block;
141 	sector_t last_block_in_file;
142 	sector_t blocks[MAX_BUF_PER_PAGE];
143 	unsigned page_block;
144 	unsigned first_hole = blocks_per_page;
145 	struct block_device *bdev = NULL;
146 	int length;
147 	int fully_mapped = 1;
148 	int op = REQ_OP_READ;
149 	unsigned nblocks;
150 	unsigned relative_block;
151 	gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
152 
153 	if (args->is_readahead) {
154 		op |= REQ_RAHEAD;
155 		gfp |= __GFP_NORETRY | __GFP_NOWARN;
156 	}
157 
158 	if (page_has_buffers(page))
159 		goto confused;
160 
161 	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
162 	last_block = block_in_file + args->nr_pages * blocks_per_page;
163 	last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
164 	if (last_block > last_block_in_file)
165 		last_block = last_block_in_file;
166 	page_block = 0;
167 
168 	/*
169 	 * Map blocks using the result from the previous get_blocks call first.
170 	 */
171 	nblocks = map_bh->b_size >> blkbits;
172 	if (buffer_mapped(map_bh) &&
173 			block_in_file > args->first_logical_block &&
174 			block_in_file < (args->first_logical_block + nblocks)) {
175 		unsigned map_offset = block_in_file - args->first_logical_block;
176 		unsigned last = nblocks - map_offset;
177 
178 		for (relative_block = 0; ; relative_block++) {
179 			if (relative_block == last) {
180 				clear_buffer_mapped(map_bh);
181 				break;
182 			}
183 			if (page_block == blocks_per_page)
184 				break;
185 			blocks[page_block] = map_bh->b_blocknr + map_offset +
186 						relative_block;
187 			page_block++;
188 			block_in_file++;
189 		}
190 		bdev = map_bh->b_bdev;
191 	}
192 
193 	/*
194 	 * Then do more get_blocks calls until we are done with this page.
195 	 */
196 	map_bh->b_page = page;
197 	while (page_block < blocks_per_page) {
198 		map_bh->b_state = 0;
199 		map_bh->b_size = 0;
200 
201 		if (block_in_file < last_block) {
202 			map_bh->b_size = (last_block-block_in_file) << blkbits;
203 			if (args->get_block(inode, block_in_file, map_bh, 0))
204 				goto confused;
205 			args->first_logical_block = block_in_file;
206 		}
207 
208 		if (!buffer_mapped(map_bh)) {
209 			fully_mapped = 0;
210 			if (first_hole == blocks_per_page)
211 				first_hole = page_block;
212 			page_block++;
213 			block_in_file++;
214 			continue;
215 		}
216 
217 		/* some filesystems will copy data into the page during
218 		 * the get_block call, in which case we don't want to
219 		 * read it again.  map_buffer_to_page copies the data
220 		 * we just collected from get_block into the page's buffers
221 		 * so readpage doesn't have to repeat the get_block call
222 		 */
223 		if (buffer_uptodate(map_bh)) {
224 			map_buffer_to_page(page, map_bh, page_block);
225 			goto confused;
226 		}
227 
228 		if (first_hole != blocks_per_page)
229 			goto confused;		/* hole -> non-hole */
230 
231 		/* Contiguous blocks? */
232 		if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
233 			goto confused;
234 		nblocks = map_bh->b_size >> blkbits;
235 		for (relative_block = 0; ; relative_block++) {
236 			if (relative_block == nblocks) {
237 				clear_buffer_mapped(map_bh);
238 				break;
239 			} else if (page_block == blocks_per_page)
240 				break;
241 			blocks[page_block] = map_bh->b_blocknr+relative_block;
242 			page_block++;
243 			block_in_file++;
244 		}
245 		bdev = map_bh->b_bdev;
246 	}
247 
248 	if (first_hole != blocks_per_page) {
249 		zero_user_segment(page, first_hole << blkbits, PAGE_SIZE);
250 		if (first_hole == 0) {
251 			SetPageUptodate(page);
252 			unlock_page(page);
253 			goto out;
254 		}
255 	} else if (fully_mapped) {
256 		SetPageMappedToDisk(page);
257 	}
258 
259 	/*
260 	 * This page will go to BIO.  Do we need to send this BIO off first?
261 	 */
262 	if (args->bio && (args->last_block_in_bio != blocks[0] - 1))
263 		args->bio = mpage_bio_submit(args->bio);
264 
265 alloc_new:
266 	if (args->bio == NULL) {
267 		if (first_hole == blocks_per_page) {
268 			if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
269 								page))
270 				goto out;
271 		}
272 		args->bio = bio_alloc(bdev, bio_max_segs(args->nr_pages), op,
273 				      gfp);
274 		if (args->bio == NULL)
275 			goto confused;
276 		args->bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
277 	}
278 
279 	length = first_hole << blkbits;
280 	if (bio_add_page(args->bio, page, length, 0) < length) {
281 		args->bio = mpage_bio_submit(args->bio);
282 		goto alloc_new;
283 	}
284 
285 	relative_block = block_in_file - args->first_logical_block;
286 	nblocks = map_bh->b_size >> blkbits;
287 	if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
288 	    (first_hole != blocks_per_page))
289 		args->bio = mpage_bio_submit(args->bio);
290 	else
291 		args->last_block_in_bio = blocks[blocks_per_page - 1];
292 out:
293 	return args->bio;
294 
295 confused:
296 	if (args->bio)
297 		args->bio = mpage_bio_submit(args->bio);
298 	if (!PageUptodate(page))
299 		block_read_full_folio(page_folio(page), args->get_block);
300 	else
301 		unlock_page(page);
302 	goto out;
303 }
304 
305 /**
306  * mpage_readahead - start reads against pages
307  * @rac: Describes which pages to read.
308  * @get_block: The filesystem's block mapper function.
309  *
310  * This function walks the pages and the blocks within each page, building and
311  * emitting large BIOs.
312  *
313  * If anything unusual happens, such as:
314  *
315  * - encountering a page which has buffers
316  * - encountering a page which has a non-hole after a hole
317  * - encountering a page with non-contiguous blocks
318  *
319  * then this code just gives up and calls the buffer_head-based read function.
320  * It does handle a page which has holes at the end - that is a common case:
321  * the end-of-file on blocksize < PAGE_SIZE setups.
322  *
323  * BH_Boundary explanation:
324  *
325  * There is a problem.  The mpage read code assembles several pages, gets all
326  * their disk mappings, and then submits them all.  That's fine, but obtaining
327  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
328  *
329  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
330  * submitted in the following order:
331  *
332  * 	12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
333  *
334  * because the indirect block has to be read to get the mappings of blocks
335  * 13,14,15,16.  Obviously, this impacts performance.
336  *
337  * So what we do it to allow the filesystem's get_block() function to set
338  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
339  * after this one will require I/O against a block which is probably close to
340  * this one.  So you should push what I/O you have currently accumulated.
341  *
342  * This all causes the disk requests to be issued in the correct order.
343  */
344 void mpage_readahead(struct readahead_control *rac, get_block_t get_block)
345 {
346 	struct page *page;
347 	struct mpage_readpage_args args = {
348 		.get_block = get_block,
349 		.is_readahead = true,
350 	};
351 
352 	while ((page = readahead_page(rac))) {
353 		prefetchw(&page->flags);
354 		args.page = page;
355 		args.nr_pages = readahead_count(rac);
356 		args.bio = do_mpage_readpage(&args);
357 		put_page(page);
358 	}
359 	if (args.bio)
360 		mpage_bio_submit(args.bio);
361 }
362 EXPORT_SYMBOL(mpage_readahead);
363 
364 /*
365  * This isn't called much at all
366  */
367 int mpage_read_folio(struct folio *folio, get_block_t get_block)
368 {
369 	struct mpage_readpage_args args = {
370 		.page = &folio->page,
371 		.nr_pages = 1,
372 		.get_block = get_block,
373 	};
374 
375 	VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
376 
377 	args.bio = do_mpage_readpage(&args);
378 	if (args.bio)
379 		mpage_bio_submit(args.bio);
380 	return 0;
381 }
382 EXPORT_SYMBOL(mpage_read_folio);
383 
384 /*
385  * Writing is not so simple.
386  *
387  * If the page has buffers then they will be used for obtaining the disk
388  * mapping.  We only support pages which are fully mapped-and-dirty, with a
389  * special case for pages which are unmapped at the end: end-of-file.
390  *
391  * If the page has no buffers (preferred) then the page is mapped here.
392  *
393  * If all blocks are found to be contiguous then the page can go into the
394  * BIO.  Otherwise fall back to the mapping's writepage().
395  *
396  * FIXME: This code wants an estimate of how many pages are still to be
397  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
398  * just allocate full-size (16-page) BIOs.
399  */
400 
401 struct mpage_data {
402 	struct bio *bio;
403 	sector_t last_block_in_bio;
404 	get_block_t *get_block;
405 	unsigned use_writepage;
406 };
407 
408 /*
409  * We have our BIO, so we can now mark the buffers clean.  Make
410  * sure to only clean buffers which we know we'll be writing.
411  */
412 static void clean_buffers(struct page *page, unsigned first_unmapped)
413 {
414 	unsigned buffer_counter = 0;
415 	struct buffer_head *bh, *head;
416 	if (!page_has_buffers(page))
417 		return;
418 	head = page_buffers(page);
419 	bh = head;
420 
421 	do {
422 		if (buffer_counter++ == first_unmapped)
423 			break;
424 		clear_buffer_dirty(bh);
425 		bh = bh->b_this_page;
426 	} while (bh != head);
427 
428 	/*
429 	 * we cannot drop the bh if the page is not uptodate or a concurrent
430 	 * read_folio would fail to serialize with the bh and it would read from
431 	 * disk before we reach the platter.
432 	 */
433 	if (buffer_heads_over_limit && PageUptodate(page))
434 		try_to_free_buffers(page_folio(page));
435 }
436 
437 /*
438  * For situations where we want to clean all buffers attached to a page.
439  * We don't need to calculate how many buffers are attached to the page,
440  * we just need to specify a number larger than the maximum number of buffers.
441  */
442 void clean_page_buffers(struct page *page)
443 {
444 	clean_buffers(page, ~0U);
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_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 				 * block_dirty_folio -> 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_folio().  If this address_space is also
516 		 * using mpage_readahead 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_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 			clean_bdev_bh_alias(&map_bh);
536 		if (buffer_boundary(&map_bh)) {
537 			boundary_block = map_bh.b_blocknr;
538 			boundary_bdev = map_bh.b_bdev;
539 		}
540 		if (page_block) {
541 			if (map_bh.b_blocknr != blocks[page_block-1] + 1)
542 				goto confused;
543 		}
544 		blocks[page_block++] = map_bh.b_blocknr;
545 		boundary = buffer_boundary(&map_bh);
546 		bdev = map_bh.b_bdev;
547 		if (block_in_file == last_block)
548 			break;
549 		block_in_file++;
550 	}
551 	BUG_ON(page_block == 0);
552 
553 	first_unmapped = page_block;
554 
555 page_is_mapped:
556 	end_index = i_size >> PAGE_SHIFT;
557 	if (page->index >= end_index) {
558 		/*
559 		 * The page straddles i_size.  It must be zeroed out on each
560 		 * and every writepage invocation because it may be mmapped.
561 		 * "A file is mapped in multiples of the page size.  For a file
562 		 * that is not a multiple of the page size, the remaining memory
563 		 * is zeroed when mapped, and writes to that region are not
564 		 * written out to the file."
565 		 */
566 		unsigned offset = i_size & (PAGE_SIZE - 1);
567 
568 		if (page->index > end_index || !offset)
569 			goto confused;
570 		zero_user_segment(page, offset, PAGE_SIZE);
571 	}
572 
573 	/*
574 	 * This page will go to BIO.  Do we need to send this BIO off first?
575 	 */
576 	if (bio && mpd->last_block_in_bio != blocks[0] - 1)
577 		bio = mpage_bio_submit(bio);
578 
579 alloc_new:
580 	if (bio == NULL) {
581 		if (first_unmapped == blocks_per_page) {
582 			if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
583 								page, wbc))
584 				goto out;
585 		}
586 		bio = bio_alloc(bdev, BIO_MAX_VECS,
587 				REQ_OP_WRITE | wbc_to_write_flags(wbc),
588 				GFP_NOFS);
589 		bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
590 		wbc_init_bio(wbc, bio);
591 	}
592 
593 	/*
594 	 * Must try to add the page before marking the buffer clean or
595 	 * the confused fail path above (OOM) will be very confused when
596 	 * it finds all bh marked clean (i.e. it will not write anything)
597 	 */
598 	wbc_account_cgroup_owner(wbc, page, PAGE_SIZE);
599 	length = first_unmapped << blkbits;
600 	if (bio_add_page(bio, page, length, 0) < length) {
601 		bio = mpage_bio_submit(bio);
602 		goto alloc_new;
603 	}
604 
605 	clean_buffers(page, first_unmapped);
606 
607 	BUG_ON(PageWriteback(page));
608 	set_page_writeback(page);
609 	unlock_page(page);
610 	if (boundary || (first_unmapped != blocks_per_page)) {
611 		bio = mpage_bio_submit(bio);
612 		if (boundary_block) {
613 			write_boundary_block(boundary_bdev,
614 					boundary_block, 1 << blkbits);
615 		}
616 	} else {
617 		mpd->last_block_in_bio = blocks[blocks_per_page - 1];
618 	}
619 	goto out;
620 
621 confused:
622 	if (bio)
623 		bio = mpage_bio_submit(bio);
624 
625 	if (mpd->use_writepage) {
626 		ret = mapping->a_ops->writepage(page, wbc);
627 	} else {
628 		ret = -EAGAIN;
629 		goto out;
630 	}
631 	/*
632 	 * The caller has a ref on the inode, so *mapping is stable
633 	 */
634 	mapping_set_error(mapping, ret);
635 out:
636 	mpd->bio = bio;
637 	return ret;
638 }
639 
640 /**
641  * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
642  * @mapping: address space structure to write
643  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
644  * @get_block: the filesystem's block mapper function.
645  *             If this is NULL then use a_ops->writepage.  Otherwise, go
646  *             direct-to-BIO.
647  *
648  * This is a library function, which implements the writepages()
649  * address_space_operation.
650  *
651  * If a page is already under I/O, generic_writepages() skips it, even
652  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
653  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
654  * and msync() need to guarantee that all the data which was dirty at the time
655  * the call was made get new I/O started against them.  If wbc->sync_mode is
656  * WB_SYNC_ALL then we were called for data integrity and we must wait for
657  * existing IO to complete.
658  */
659 int
660 mpage_writepages(struct address_space *mapping,
661 		struct writeback_control *wbc, get_block_t get_block)
662 {
663 	struct blk_plug plug;
664 	int ret;
665 
666 	blk_start_plug(&plug);
667 
668 	if (!get_block)
669 		ret = generic_writepages(mapping, wbc);
670 	else {
671 		struct mpage_data mpd = {
672 			.bio = NULL,
673 			.last_block_in_bio = 0,
674 			.get_block = get_block,
675 			.use_writepage = 1,
676 		};
677 
678 		ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
679 		if (mpd.bio)
680 			mpage_bio_submit(mpd.bio);
681 	}
682 	blk_finish_plug(&plug);
683 	return ret;
684 }
685 EXPORT_SYMBOL(mpage_writepages);
686 
687 int mpage_writepage(struct page *page, get_block_t get_block,
688 	struct writeback_control *wbc)
689 {
690 	struct mpage_data mpd = {
691 		.bio = NULL,
692 		.last_block_in_bio = 0,
693 		.get_block = get_block,
694 		.use_writepage = 0,
695 	};
696 	int ret = __mpage_writepage(page, wbc, &mpd);
697 	if (mpd.bio)
698 		mpage_bio_submit(mpd.bio);
699 	return ret;
700 }
701 EXPORT_SYMBOL(mpage_writepage);
702