4 * Copyright (C) 2002, Linus Torvalds.
6 * Contains functions related to preparing and submitting BIOs which contain
7 * multiple pagecache pages.
9 * 15May2002 Andrew Morton
11 * 27Jun2002 axboe@suse.de
12 * use bio_add_page() to build bio's just the right size
15 #include <linux/kernel.h>
16 #include <linux/export.h>
18 #include <linux/kdev_t.h>
19 #include <linux/gfp.h>
20 #include <linux/bio.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>
33 #define CREATE_TRACE_POINTS
34 #include <trace/events/android_fs.h>
36 EXPORT_TRACEPOINT_SYMBOL(android_fs_datawrite_start
);
37 EXPORT_TRACEPOINT_SYMBOL(android_fs_datawrite_end
);
38 EXPORT_TRACEPOINT_SYMBOL(android_fs_dataread_start
);
39 EXPORT_TRACEPOINT_SYMBOL(android_fs_dataread_end
);
42 * I/O completion handler for multipage BIOs.
44 * The mpage code never puts partial pages into a BIO (except for end-of-file).
45 * If a page does not map to a contiguous run of blocks then it simply falls
46 * back to block_read_full_page().
48 * Why is this? If a page's completion depends on a number of different BIOs
49 * which can complete in any order (or at the same time) then determining the
50 * status of that page is hard. See end_buffer_async_read() for the details.
51 * There is no point in duplicating all that complexity.
53 static void mpage_end_io(struct bio
*bio
)
58 if (trace_android_fs_dataread_end_enabled() &&
59 (bio_data_dir(bio
) == READ
)) {
60 struct page
*first_page
= bio
->bi_io_vec
[0].bv_page
;
62 if (first_page
!= NULL
)
63 trace_android_fs_dataread_end(first_page
->mapping
->host
,
64 page_offset(first_page
),
65 bio
->bi_iter
.bi_size
);
68 bio_for_each_segment_all(bv
, bio
, i
) {
69 struct page
*page
= bv
->bv_page
;
70 page_endio(page
, bio_data_dir(bio
), bio
->bi_error
);
76 static struct bio
*mpage_bio_submit(int rw
, struct bio
*bio
)
78 if (trace_android_fs_dataread_start_enabled() && (rw
== READ
)) {
79 struct page
*first_page
= bio
->bi_io_vec
[0].bv_page
;
81 if (first_page
!= NULL
) {
82 char *path
, pathbuf
[MAX_TRACE_PATHBUF_LEN
];
84 path
= android_fstrace_get_pathname(pathbuf
,
85 MAX_TRACE_PATHBUF_LEN
,
86 first_page
->mapping
->host
);
87 trace_android_fs_dataread_start(
88 first_page
->mapping
->host
,
89 page_offset(first_page
),
96 bio
->bi_end_io
= mpage_end_io
;
97 guard_bio_eod(rw
, bio
);
103 mpage_alloc(struct block_device
*bdev
,
104 sector_t first_sector
, int nr_vecs
,
109 bio
= bio_alloc(gfp_flags
, nr_vecs
);
111 if (bio
== NULL
&& (current
->flags
& PF_MEMALLOC
)) {
112 while (!bio
&& (nr_vecs
/= 2))
113 bio
= bio_alloc(gfp_flags
, nr_vecs
);
118 bio
->bi_iter
.bi_sector
= first_sector
;
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
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.
134 map_buffer_to_page(struct page
*page
, struct buffer_head
*bh
, int page_block
)
136 struct inode
*inode
= page
->mapping
->host
;
137 struct buffer_head
*page_bh
, *head
;
140 if (!page_has_buffers(page
)) {
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
145 if (inode
->i_blkbits
== PAGE_CACHE_SHIFT
&&
146 buffer_uptodate(bh
)) {
147 SetPageUptodate(page
);
150 create_empty_buffers(page
, i_blocksize(inode
), 0);
152 head
= page_buffers(page
);
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
;
161 page_bh
= page_bh
->b_this_page
;
163 } while (page_bh
!= head
);
167 * This is the worker routine which does all the work of mapping the disk
168 * blocks and constructs largest possible bios, submits them for IO if the
169 * blocks are not contiguous on the disk.
171 * We pass a buffer_head back and forth and use its buffer_mapped() flag to
172 * represent the validity of its disk mapping and to decide when to do the next
176 do_mpage_readpage(struct bio
*bio
, struct page
*page
, unsigned nr_pages
,
177 sector_t
*last_block_in_bio
, struct buffer_head
*map_bh
,
178 unsigned long *first_logical_block
, get_block_t get_block
,
181 struct inode
*inode
= page
->mapping
->host
;
182 const unsigned blkbits
= inode
->i_blkbits
;
183 const unsigned blocks_per_page
= PAGE_CACHE_SIZE
>> blkbits
;
184 const unsigned blocksize
= 1 << blkbits
;
185 sector_t block_in_file
;
187 sector_t last_block_in_file
;
188 sector_t blocks
[MAX_BUF_PER_PAGE
];
190 unsigned first_hole
= blocks_per_page
;
191 struct block_device
*bdev
= NULL
;
193 int fully_mapped
= 1;
195 unsigned relative_block
;
197 if (page_has_buffers(page
))
200 block_in_file
= (sector_t
)page
->index
<< (PAGE_CACHE_SHIFT
- blkbits
);
201 last_block
= block_in_file
+ nr_pages
* blocks_per_page
;
202 last_block_in_file
= (i_size_read(inode
) + blocksize
- 1) >> blkbits
;
203 if (last_block
> last_block_in_file
)
204 last_block
= last_block_in_file
;
208 * Map blocks using the result from the previous get_blocks call first.
210 nblocks
= map_bh
->b_size
>> blkbits
;
211 if (buffer_mapped(map_bh
) && block_in_file
> *first_logical_block
&&
212 block_in_file
< (*first_logical_block
+ nblocks
)) {
213 unsigned map_offset
= block_in_file
- *first_logical_block
;
214 unsigned last
= nblocks
- map_offset
;
216 for (relative_block
= 0; ; relative_block
++) {
217 if (relative_block
== last
) {
218 clear_buffer_mapped(map_bh
);
221 if (page_block
== blocks_per_page
)
223 blocks
[page_block
] = map_bh
->b_blocknr
+ map_offset
+
228 bdev
= map_bh
->b_bdev
;
232 * Then do more get_blocks calls until we are done with this page.
234 map_bh
->b_page
= page
;
235 while (page_block
< blocks_per_page
) {
239 if (block_in_file
< last_block
) {
240 map_bh
->b_size
= (last_block
-block_in_file
) << blkbits
;
241 if (get_block(inode
, block_in_file
, map_bh
, 0))
243 *first_logical_block
= block_in_file
;
246 if (!buffer_mapped(map_bh
)) {
248 if (first_hole
== blocks_per_page
)
249 first_hole
= page_block
;
255 /* some filesystems will copy data into the page during
256 * the get_block call, in which case we don't want to
257 * read it again. map_buffer_to_page copies the data
258 * we just collected from get_block into the page's buffers
259 * so readpage doesn't have to repeat the get_block call
261 if (buffer_uptodate(map_bh
)) {
262 map_buffer_to_page(page
, map_bh
, page_block
);
266 if (first_hole
!= blocks_per_page
)
267 goto confused
; /* hole -> non-hole */
269 /* Contiguous blocks? */
270 if (page_block
&& blocks
[page_block
-1] != map_bh
->b_blocknr
-1)
272 nblocks
= map_bh
->b_size
>> blkbits
;
273 for (relative_block
= 0; ; relative_block
++) {
274 if (relative_block
== nblocks
) {
275 clear_buffer_mapped(map_bh
);
277 } else if (page_block
== blocks_per_page
)
279 blocks
[page_block
] = map_bh
->b_blocknr
+relative_block
;
283 bdev
= map_bh
->b_bdev
;
286 if (first_hole
!= blocks_per_page
) {
287 zero_user_segment(page
, first_hole
<< blkbits
, PAGE_CACHE_SIZE
);
288 if (first_hole
== 0) {
289 SetPageUptodate(page
);
293 } else if (fully_mapped
) {
294 SetPageMappedToDisk(page
);
297 if (fully_mapped
&& blocks_per_page
== 1 && !PageUptodate(page
) &&
298 cleancache_get_page(page
) == 0) {
299 SetPageUptodate(page
);
304 * This page will go to BIO. Do we need to send this BIO off first?
306 if (bio
&& (*last_block_in_bio
!= blocks
[0] - 1))
307 bio
= mpage_bio_submit(READ
, bio
);
311 if (first_hole
== blocks_per_page
) {
312 if (!bdev_read_page(bdev
, blocks
[0] << (blkbits
- 9),
316 bio
= mpage_alloc(bdev
, blocks
[0] << (blkbits
- 9),
317 min_t(int, nr_pages
, BIO_MAX_PAGES
), gfp
);
322 length
= first_hole
<< blkbits
;
323 if (bio_add_page(bio
, page
, length
, 0) < length
) {
324 bio
= mpage_bio_submit(READ
, bio
);
328 relative_block
= block_in_file
- *first_logical_block
;
329 nblocks
= map_bh
->b_size
>> blkbits
;
330 if ((buffer_boundary(map_bh
) && relative_block
== nblocks
) ||
331 (first_hole
!= blocks_per_page
))
332 bio
= mpage_bio_submit(READ
, bio
);
334 *last_block_in_bio
= blocks
[blocks_per_page
- 1];
340 bio
= mpage_bio_submit(READ
, bio
);
341 if (!PageUptodate(page
))
342 block_read_full_page(page
, get_block
);
349 * mpage_readpages - populate an address space with some pages & start reads against them
350 * @mapping: the address_space
351 * @pages: The address of a list_head which contains the target pages. These
352 * pages have their ->index populated and are otherwise uninitialised.
353 * The page at @pages->prev has the lowest file offset, and reads should be
354 * issued in @pages->prev to @pages->next order.
355 * @nr_pages: The number of pages at *@pages
356 * @get_block: The filesystem's block mapper function.
358 * This function walks the pages and the blocks within each page, building and
359 * emitting large BIOs.
361 * If anything unusual happens, such as:
363 * - encountering a page which has buffers
364 * - encountering a page which has a non-hole after a hole
365 * - encountering a page with non-contiguous blocks
367 * then this code just gives up and calls the buffer_head-based read function.
368 * It does handle a page which has holes at the end - that is a common case:
369 * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
371 * BH_Boundary explanation:
373 * There is a problem. The mpage read code assembles several pages, gets all
374 * their disk mappings, and then submits them all. That's fine, but obtaining
375 * the disk mappings may require I/O. Reads of indirect blocks, for example.
377 * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
378 * submitted in the following order:
379 * 12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
381 * because the indirect block has to be read to get the mappings of blocks
382 * 13,14,15,16. Obviously, this impacts performance.
384 * So what we do it to allow the filesystem's get_block() function to set
385 * BH_Boundary when it maps block 11. BH_Boundary says: mapping of the block
386 * after this one will require I/O against a block which is probably close to
387 * this one. So you should push what I/O you have currently accumulated.
389 * This all causes the disk requests to be issued in the correct order.
392 mpage_readpages(struct address_space
*mapping
, struct list_head
*pages
,
393 unsigned nr_pages
, get_block_t get_block
)
395 struct bio
*bio
= NULL
;
397 sector_t last_block_in_bio
= 0;
398 struct buffer_head map_bh
;
399 unsigned long first_logical_block
= 0;
400 gfp_t gfp
= mapping_gfp_constraint(mapping
, GFP_KERNEL
);
404 for (page_idx
= 0; page_idx
< nr_pages
; page_idx
++) {
405 struct page
*page
= list_entry(pages
->prev
, struct page
, lru
);
407 prefetchw(&page
->flags
);
408 list_del(&page
->lru
);
409 if (!add_to_page_cache_lru(page
, mapping
,
412 bio
= do_mpage_readpage(bio
, page
,
414 &last_block_in_bio
, &map_bh
,
415 &first_logical_block
,
418 page_cache_release(page
);
420 BUG_ON(!list_empty(pages
));
422 mpage_bio_submit(READ
, bio
);
425 EXPORT_SYMBOL(mpage_readpages
);
428 * This isn't called much at all
430 int mpage_readpage(struct page
*page
, get_block_t get_block
)
432 struct bio
*bio
= NULL
;
433 sector_t last_block_in_bio
= 0;
434 struct buffer_head map_bh
;
435 unsigned long first_logical_block
= 0;
436 gfp_t gfp
= mapping_gfp_constraint(page
->mapping
, GFP_KERNEL
);
440 bio
= do_mpage_readpage(bio
, page
, 1, &last_block_in_bio
,
441 &map_bh
, &first_logical_block
, get_block
, gfp
);
443 mpage_bio_submit(READ
, bio
);
446 EXPORT_SYMBOL(mpage_readpage
);
449 * Writing is not so simple.
451 * If the page has buffers then they will be used for obtaining the disk
452 * mapping. We only support pages which are fully mapped-and-dirty, with a
453 * special case for pages which are unmapped at the end: end-of-file.
455 * If the page has no buffers (preferred) then the page is mapped here.
457 * If all blocks are found to be contiguous then the page can go into the
458 * BIO. Otherwise fall back to the mapping's writepage().
460 * FIXME: This code wants an estimate of how many pages are still to be
461 * written, so it can intelligently allocate a suitably-sized BIO. For now,
462 * just allocate full-size (16-page) BIOs.
467 sector_t last_block_in_bio
;
468 get_block_t
*get_block
;
469 unsigned use_writepage
;
473 * We have our BIO, so we can now mark the buffers clean. Make
474 * sure to only clean buffers which we know we'll be writing.
476 static void clean_buffers(struct page
*page
, unsigned first_unmapped
)
478 unsigned buffer_counter
= 0;
479 struct buffer_head
*bh
, *head
;
480 if (!page_has_buffers(page
))
482 head
= page_buffers(page
);
486 if (buffer_counter
++ == first_unmapped
)
488 clear_buffer_dirty(bh
);
489 bh
= bh
->b_this_page
;
490 } while (bh
!= head
);
493 * we cannot drop the bh if the page is not uptodate or a concurrent
494 * readpage would fail to serialize with the bh and it would read from
495 * disk before we reach the platter.
497 if (buffer_heads_over_limit
&& PageUptodate(page
))
498 try_to_free_buffers(page
);
501 static int __mpage_writepage(struct page
*page
, struct writeback_control
*wbc
,
504 struct mpage_data
*mpd
= data
;
505 struct bio
*bio
= mpd
->bio
;
506 struct address_space
*mapping
= page
->mapping
;
507 struct inode
*inode
= page
->mapping
->host
;
508 const unsigned blkbits
= inode
->i_blkbits
;
509 unsigned long end_index
;
510 const unsigned blocks_per_page
= PAGE_CACHE_SIZE
>> blkbits
;
512 sector_t block_in_file
;
513 sector_t blocks
[MAX_BUF_PER_PAGE
];
515 unsigned first_unmapped
= blocks_per_page
;
516 struct block_device
*bdev
= NULL
;
518 sector_t boundary_block
= 0;
519 struct block_device
*boundary_bdev
= NULL
;
521 struct buffer_head map_bh
;
522 loff_t i_size
= i_size_read(inode
);
524 int wr
= (wbc
->sync_mode
== WB_SYNC_ALL
? WRITE_SYNC
: WRITE
);
526 if (page_has_buffers(page
)) {
527 struct buffer_head
*head
= page_buffers(page
);
528 struct buffer_head
*bh
= head
;
530 /* If they're all mapped and dirty, do it */
533 BUG_ON(buffer_locked(bh
));
534 if (!buffer_mapped(bh
)) {
536 * unmapped dirty buffers are created by
537 * __set_page_dirty_buffers -> mmapped data
539 if (buffer_dirty(bh
))
541 if (first_unmapped
== blocks_per_page
)
542 first_unmapped
= page_block
;
546 if (first_unmapped
!= blocks_per_page
)
547 goto confused
; /* hole -> non-hole */
549 if (!buffer_dirty(bh
) || !buffer_uptodate(bh
))
552 if (bh
->b_blocknr
!= blocks
[page_block
-1] + 1)
555 blocks
[page_block
++] = bh
->b_blocknr
;
556 boundary
= buffer_boundary(bh
);
558 boundary_block
= bh
->b_blocknr
;
559 boundary_bdev
= bh
->b_bdev
;
562 } while ((bh
= bh
->b_this_page
) != head
);
568 * Page has buffers, but they are all unmapped. The page was
569 * created by pagein or read over a hole which was handled by
570 * block_read_full_page(). If this address_space is also
571 * using mpage_readpages then this can rarely happen.
577 * The page has no buffers: map it to disk
579 BUG_ON(!PageUptodate(page
));
580 block_in_file
= (sector_t
)page
->index
<< (PAGE_CACHE_SHIFT
- blkbits
);
581 last_block
= (i_size
- 1) >> blkbits
;
582 map_bh
.b_page
= page
;
583 for (page_block
= 0; page_block
< blocks_per_page
; ) {
586 map_bh
.b_size
= 1 << blkbits
;
587 if (mpd
->get_block(inode
, block_in_file
, &map_bh
, 1))
589 if (buffer_new(&map_bh
))
590 unmap_underlying_metadata(map_bh
.b_bdev
,
592 if (buffer_boundary(&map_bh
)) {
593 boundary_block
= map_bh
.b_blocknr
;
594 boundary_bdev
= map_bh
.b_bdev
;
597 if (map_bh
.b_blocknr
!= blocks
[page_block
-1] + 1)
600 blocks
[page_block
++] = map_bh
.b_blocknr
;
601 boundary
= buffer_boundary(&map_bh
);
602 bdev
= map_bh
.b_bdev
;
603 if (block_in_file
== last_block
)
607 BUG_ON(page_block
== 0);
609 first_unmapped
= page_block
;
612 end_index
= i_size
>> PAGE_CACHE_SHIFT
;
613 if (page
->index
>= end_index
) {
615 * The page straddles i_size. It must be zeroed out on each
616 * and every writepage invocation because it may be mmapped.
617 * "A file is mapped in multiples of the page size. For a file
618 * that is not a multiple of the page size, the remaining memory
619 * is zeroed when mapped, and writes to that region are not
620 * written out to the file."
622 unsigned offset
= i_size
& (PAGE_CACHE_SIZE
- 1);
624 if (page
->index
> end_index
|| !offset
)
626 zero_user_segment(page
, offset
, PAGE_CACHE_SIZE
);
630 * This page will go to BIO. Do we need to send this BIO off first?
632 if (bio
&& mpd
->last_block_in_bio
!= blocks
[0] - 1)
633 bio
= mpage_bio_submit(wr
, bio
);
637 if (first_unmapped
== blocks_per_page
) {
638 if (!bdev_write_page(bdev
, blocks
[0] << (blkbits
- 9),
640 clean_buffers(page
, first_unmapped
);
644 bio
= mpage_alloc(bdev
, blocks
[0] << (blkbits
- 9),
645 BIO_MAX_PAGES
, GFP_NOFS
|__GFP_HIGH
);
649 wbc_init_bio(wbc
, bio
);
653 * Must try to add the page before marking the buffer clean or
654 * the confused fail path above (OOM) will be very confused when
655 * it finds all bh marked clean (i.e. it will not write anything)
657 wbc_account_io(wbc
, page
, PAGE_SIZE
);
658 length
= first_unmapped
<< blkbits
;
659 if (bio_add_page(bio
, page
, length
, 0) < length
) {
660 bio
= mpage_bio_submit(wr
, bio
);
664 clean_buffers(page
, first_unmapped
);
666 BUG_ON(PageWriteback(page
));
667 set_page_writeback(page
);
669 if (boundary
|| (first_unmapped
!= blocks_per_page
)) {
670 bio
= mpage_bio_submit(wr
, bio
);
671 if (boundary_block
) {
672 write_boundary_block(boundary_bdev
,
673 boundary_block
, 1 << blkbits
);
676 mpd
->last_block_in_bio
= blocks
[blocks_per_page
- 1];
682 bio
= mpage_bio_submit(wr
, bio
);
684 if (mpd
->use_writepage
) {
685 ret
= mapping
->a_ops
->writepage(page
, wbc
);
691 * The caller has a ref on the inode, so *mapping is stable
693 mapping_set_error(mapping
, ret
);
700 * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
701 * @mapping: address space structure to write
702 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
703 * @get_block: the filesystem's block mapper function.
704 * If this is NULL then use a_ops->writepage. Otherwise, go
707 * This is a library function, which implements the writepages()
708 * address_space_operation.
710 * If a page is already under I/O, generic_writepages() skips it, even
711 * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
712 * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
713 * and msync() need to guarantee that all the data which was dirty at the time
714 * the call was made get new I/O started against them. If wbc->sync_mode is
715 * WB_SYNC_ALL then we were called for data integrity and we must wait for
716 * existing IO to complete.
719 mpage_writepages(struct address_space
*mapping
,
720 struct writeback_control
*wbc
, get_block_t get_block
)
722 struct blk_plug plug
;
725 blk_start_plug(&plug
);
728 ret
= generic_writepages(mapping
, wbc
);
730 struct mpage_data mpd
= {
732 .last_block_in_bio
= 0,
733 .get_block
= get_block
,
737 ret
= write_cache_pages(mapping
, wbc
, __mpage_writepage
, &mpd
);
739 int wr
= (wbc
->sync_mode
== WB_SYNC_ALL
?
741 mpage_bio_submit(wr
, mpd
.bio
);
744 blk_finish_plug(&plug
);
747 EXPORT_SYMBOL(mpage_writepages
);
749 int mpage_writepage(struct page
*page
, get_block_t get_block
,
750 struct writeback_control
*wbc
)
752 struct mpage_data mpd
= {
754 .last_block_in_bio
= 0,
755 .get_block
= get_block
,
758 int ret
= __mpage_writepage(page
, wbc
, &mpd
);
760 int wr
= (wbc
->sync_mode
== WB_SYNC_ALL
?
762 mpage_bio_submit(wr
, mpd
.bio
);
766 EXPORT_SYMBOL(mpage_writepage
);