| // SPDX-License-Identifier: GPL-2.0 |
| /* |
| * fs/mpage.c |
| * |
| * Copyright (C) 2002, Linus Torvalds. |
| * |
| * Contains functions related to preparing and submitting BIOs which contain |
| * multiple pagecache pages. |
| * |
| * 15May2002 Andrew Morton |
| * Initial version |
| * 27Jun2002 axboe@suse.de |
| * use bio_add_page() to build bio's just the right size |
| */ |
| |
| #include <linux/kernel.h> |
| #include <linux/export.h> |
| #include <linux/mm.h> |
| #include <linux/kdev_t.h> |
| #include <linux/gfp.h> |
| #include <linux/bio.h> |
| #include <linux/fs.h> |
| #include <linux/buffer_head.h> |
| #include <linux/blkdev.h> |
| #include <linux/highmem.h> |
| #include <linux/prefetch.h> |
| #include <linux/mpage.h> |
| #include <linux/mm_inline.h> |
| #include <linux/writeback.h> |
| #include <linux/backing-dev.h> |
| #include <linux/pagevec.h> |
| #include "internal.h" |
| |
| /* |
| * I/O completion handler for multipage BIOs. |
| * |
| * The mpage code never puts partial pages into a BIO (except for end-of-file). |
| * If a page does not map to a contiguous run of blocks then it simply falls |
| * back to block_read_full_folio(). |
| * |
| * Why is this? If a page's completion depends on a number of different BIOs |
| * which can complete in any order (or at the same time) then determining the |
| * status of that page is hard. See end_buffer_async_read() for the details. |
| * There is no point in duplicating all that complexity. |
| */ |
| static void mpage_end_io(struct bio *bio) |
| { |
| struct bio_vec *bv; |
| struct bvec_iter_all iter_all; |
| |
| bio_for_each_segment_all(bv, bio, iter_all) { |
| struct page *page = bv->bv_page; |
| page_endio(page, bio_op(bio), |
| blk_status_to_errno(bio->bi_status)); |
| } |
| |
| bio_put(bio); |
| } |
| |
| static struct bio *mpage_bio_submit(struct bio *bio) |
| { |
| bio->bi_end_io = mpage_end_io; |
| guard_bio_eod(bio); |
| submit_bio(bio); |
| return NULL; |
| } |
| |
| /* |
| * support function for mpage_readahead. The fs supplied get_block might |
| * return an up to date buffer. This is used to map that buffer into |
| * the page, which allows read_folio to avoid triggering a duplicate call |
| * to get_block. |
| * |
| * The idea is to avoid adding buffers to pages that don't already have |
| * them. So when the buffer is up to date and the page size == block size, |
| * this marks the page up to date instead of adding new buffers. |
| */ |
| static void map_buffer_to_folio(struct folio *folio, struct buffer_head *bh, |
| int page_block) |
| { |
| struct inode *inode = folio->mapping->host; |
| struct buffer_head *page_bh, *head; |
| int block = 0; |
| |
| head = folio_buffers(folio); |
| if (!head) { |
| /* |
| * don't make any buffers if there is only one buffer on |
| * the folio and the folio just needs to be set up to date |
| */ |
| if (inode->i_blkbits == PAGE_SHIFT && |
| buffer_uptodate(bh)) { |
| folio_mark_uptodate(folio); |
| return; |
| } |
| create_empty_buffers(&folio->page, i_blocksize(inode), 0); |
| head = folio_buffers(folio); |
| } |
| |
| page_bh = head; |
| do { |
| if (block == page_block) { |
| page_bh->b_state = bh->b_state; |
| page_bh->b_bdev = bh->b_bdev; |
| page_bh->b_blocknr = bh->b_blocknr; |
| break; |
| } |
| page_bh = page_bh->b_this_page; |
| block++; |
| } while (page_bh != head); |
| } |
| |
| struct mpage_readpage_args { |
| struct bio *bio; |
| struct folio *folio; |
| unsigned int nr_pages; |
| bool is_readahead; |
| sector_t last_block_in_bio; |
| struct buffer_head map_bh; |
| unsigned long first_logical_block; |
| get_block_t *get_block; |
| }; |
| |
| /* |
| * This is the worker routine which does all the work of mapping the disk |
| * blocks and constructs largest possible bios, submits them for IO if the |
| * blocks are not contiguous on the disk. |
| * |
| * We pass a buffer_head back and forth and use its buffer_mapped() flag to |
| * represent the validity of its disk mapping and to decide when to do the next |
| * get_block() call. |
| */ |
| static struct bio *do_mpage_readpage(struct mpage_readpage_args *args) |
| { |
| struct folio *folio = args->folio; |
| struct inode *inode = folio->mapping->host; |
| const unsigned blkbits = inode->i_blkbits; |
| const unsigned blocks_per_page = PAGE_SIZE >> blkbits; |
| const unsigned blocksize = 1 << blkbits; |
| struct buffer_head *map_bh = &args->map_bh; |
| sector_t block_in_file; |
| sector_t last_block; |
| sector_t last_block_in_file; |
| sector_t blocks[MAX_BUF_PER_PAGE]; |
| unsigned page_block; |
| unsigned first_hole = blocks_per_page; |
| struct block_device *bdev = NULL; |
| int length; |
| int fully_mapped = 1; |
| blk_opf_t opf = REQ_OP_READ; |
| unsigned nblocks; |
| unsigned relative_block; |
| gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL); |
| |
| /* MAX_BUF_PER_PAGE, for example */ |
| VM_BUG_ON_FOLIO(folio_test_large(folio), folio); |
| |
| if (args->is_readahead) { |
| opf |= REQ_RAHEAD; |
| gfp |= __GFP_NORETRY | __GFP_NOWARN; |
| } |
| |
| if (folio_buffers(folio)) |
| goto confused; |
| |
| block_in_file = (sector_t)folio->index << (PAGE_SHIFT - blkbits); |
| last_block = block_in_file + args->nr_pages * blocks_per_page; |
| last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits; |
| if (last_block > last_block_in_file) |
| last_block = last_block_in_file; |
| page_block = 0; |
| |
| /* |
| * Map blocks using the result from the previous get_blocks call first. |
| */ |
| nblocks = map_bh->b_size >> blkbits; |
| if (buffer_mapped(map_bh) && |
| block_in_file > args->first_logical_block && |
| block_in_file < (args->first_logical_block + nblocks)) { |
| unsigned map_offset = block_in_file - args->first_logical_block; |
| unsigned last = nblocks - map_offset; |
| |
| for (relative_block = 0; ; relative_block++) { |
| if (relative_block == last) { |
| clear_buffer_mapped(map_bh); |
| break; |
| } |
| if (page_block == blocks_per_page) |
| break; |
| blocks[page_block] = map_bh->b_blocknr + map_offset + |
| relative_block; |
| page_block++; |
| block_in_file++; |
| } |
| bdev = map_bh->b_bdev; |
| } |
| |
| /* |
| * Then do more get_blocks calls until we are done with this folio. |
| */ |
| map_bh->b_folio = folio; |
| while (page_block < blocks_per_page) { |
| map_bh->b_state = 0; |
| map_bh->b_size = 0; |
| |
| if (block_in_file < last_block) { |
| map_bh->b_size = (last_block-block_in_file) << blkbits; |
| if (args->get_block(inode, block_in_file, map_bh, 0)) |
| goto confused; |
| args->first_logical_block = block_in_file; |
| } |
| |
| if (!buffer_mapped(map_bh)) { |
| fully_mapped = 0; |
| if (first_hole == blocks_per_page) |
| first_hole = page_block; |
| page_block++; |
| block_in_file++; |
| continue; |
| } |
| |
| /* some filesystems will copy data into the page during |
| * the get_block call, in which case we don't want to |
| * read it again. map_buffer_to_folio copies the data |
| * we just collected from get_block into the folio's buffers |
| * so read_folio doesn't have to repeat the get_block call |
| */ |
| if (buffer_uptodate(map_bh)) { |
| map_buffer_to_folio(folio, map_bh, page_block); |
| goto confused; |
| } |
| |
| if (first_hole != blocks_per_page) |
| goto confused; /* hole -> non-hole */ |
| |
| /* Contiguous blocks? */ |
| if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1) |
| goto confused; |
| nblocks = map_bh->b_size >> blkbits; |
| for (relative_block = 0; ; relative_block++) { |
| if (relative_block == nblocks) { |
| clear_buffer_mapped(map_bh); |
| break; |
| } else if (page_block == blocks_per_page) |
| break; |
| blocks[page_block] = map_bh->b_blocknr+relative_block; |
| page_block++; |
| block_in_file++; |
| } |
| bdev = map_bh->b_bdev; |
| } |
| |
| if (first_hole != blocks_per_page) { |
| folio_zero_segment(folio, first_hole << blkbits, PAGE_SIZE); |
| if (first_hole == 0) { |
| folio_mark_uptodate(folio); |
| folio_unlock(folio); |
| goto out; |
| } |
| } else if (fully_mapped) { |
| folio_set_mappedtodisk(folio); |
| } |
| |
| /* |
| * This folio will go to BIO. Do we need to send this BIO off first? |
| */ |
| if (args->bio && (args->last_block_in_bio != blocks[0] - 1)) |
| args->bio = mpage_bio_submit(args->bio); |
| |
| alloc_new: |
| if (args->bio == NULL) { |
| args->bio = bio_alloc(bdev, bio_max_segs(args->nr_pages), opf, |
| gfp); |
| if (args->bio == NULL) |
| goto confused; |
| args->bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9); |
| } |
| |
| length = first_hole << blkbits; |
| if (!bio_add_folio(args->bio, folio, length, 0)) { |
| args->bio = mpage_bio_submit(args->bio); |
| goto alloc_new; |
| } |
| |
| relative_block = block_in_file - args->first_logical_block; |
| nblocks = map_bh->b_size >> blkbits; |
| if ((buffer_boundary(map_bh) && relative_block == nblocks) || |
| (first_hole != blocks_per_page)) |
| args->bio = mpage_bio_submit(args->bio); |
| else |
| args->last_block_in_bio = blocks[blocks_per_page - 1]; |
| out: |
| return args->bio; |
| |
| confused: |
| if (args->bio) |
| args->bio = mpage_bio_submit(args->bio); |
| if (!folio_test_uptodate(folio)) |
| block_read_full_folio(folio, args->get_block); |
| else |
| folio_unlock(folio); |
| goto out; |
| } |
| |
| /** |
| * mpage_readahead - start reads against pages |
| * @rac: Describes which pages to read. |
| * @get_block: The filesystem's block mapper function. |
| * |
| * This function walks the pages and the blocks within each page, building and |
| * emitting large BIOs. |
| * |
| * If anything unusual happens, such as: |
| * |
| * - encountering a page which has buffers |
| * - encountering a page which has a non-hole after a hole |
| * - encountering a page with non-contiguous blocks |
| * |
| * then this code just gives up and calls the buffer_head-based read function. |
| * It does handle a page which has holes at the end - that is a common case: |
| * the end-of-file on blocksize < PAGE_SIZE setups. |
| * |
| * BH_Boundary explanation: |
| * |
| * There is a problem. The mpage read code assembles several pages, gets all |
| * their disk mappings, and then submits them all. That's fine, but obtaining |
| * the disk mappings may require I/O. Reads of indirect blocks, for example. |
| * |
| * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be |
| * submitted in the following order: |
| * |
| * 12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16 |
| * |
| * because the indirect block has to be read to get the mappings of blocks |
| * 13,14,15,16. Obviously, this impacts performance. |
| * |
| * So what we do it to allow the filesystem's get_block() function to set |
| * BH_Boundary when it maps block 11. BH_Boundary says: mapping of the block |
| * after this one will require I/O against a block which is probably close to |
| * this one. So you should push what I/O you have currently accumulated. |
| * |
| * This all causes the disk requests to be issued in the correct order. |
| */ |
| void mpage_readahead(struct readahead_control *rac, get_block_t get_block) |
| { |
| struct folio *folio; |
| struct mpage_readpage_args args = { |
| .get_block = get_block, |
| .is_readahead = true, |
| }; |
| |
| while ((folio = readahead_folio(rac))) { |
| prefetchw(&folio->flags); |
| args.folio = folio; |
| args.nr_pages = readahead_count(rac); |
| args.bio = do_mpage_readpage(&args); |
| } |
| if (args.bio) |
| mpage_bio_submit(args.bio); |
| } |
| EXPORT_SYMBOL(mpage_readahead); |
| |
| /* |
| * This isn't called much at all |
| */ |
| int mpage_read_folio(struct folio *folio, get_block_t get_block) |
| { |
| struct mpage_readpage_args args = { |
| .folio = folio, |
| .nr_pages = 1, |
| .get_block = get_block, |
| }; |
| |
| args.bio = do_mpage_readpage(&args); |
| if (args.bio) |
| mpage_bio_submit(args.bio); |
| return 0; |
| } |
| EXPORT_SYMBOL(mpage_read_folio); |
| |
| /* |
| * Writing is not so simple. |
| * |
| * If the page has buffers then they will be used for obtaining the disk |
| * mapping. We only support pages which are fully mapped-and-dirty, with a |
| * special case for pages which are unmapped at the end: end-of-file. |
| * |
| * If the page has no buffers (preferred) then the page is mapped here. |
| * |
| * If all blocks are found to be contiguous then the page can go into the |
| * BIO. Otherwise fall back to the mapping's writepage(). |
| * |
| * FIXME: This code wants an estimate of how many pages are still to be |
| * written, so it can intelligently allocate a suitably-sized BIO. For now, |
| * just allocate full-size (16-page) BIOs. |
| */ |
| |
| struct mpage_data { |
| struct bio *bio; |
| sector_t last_block_in_bio; |
| get_block_t *get_block; |
| }; |
| |
| /* |
| * We have our BIO, so we can now mark the buffers clean. Make |
| * sure to only clean buffers which we know we'll be writing. |
| */ |
| static void clean_buffers(struct page *page, unsigned first_unmapped) |
| { |
| unsigned buffer_counter = 0; |
| struct buffer_head *bh, *head; |
| if (!page_has_buffers(page)) |
| return; |
| head = page_buffers(page); |
| bh = head; |
| |
| do { |
| if (buffer_counter++ == first_unmapped) |
| break; |
| clear_buffer_dirty(bh); |
| bh = bh->b_this_page; |
| } while (bh != head); |
| |
| /* |
| * we cannot drop the bh if the page is not uptodate or a concurrent |
| * read_folio would fail to serialize with the bh and it would read from |
| * disk before we reach the platter. |
| */ |
| if (buffer_heads_over_limit && PageUptodate(page)) |
| try_to_free_buffers(page_folio(page)); |
| } |
| |
| /* |
| * For situations where we want to clean all buffers attached to a page. |
| * We don't need to calculate how many buffers are attached to the page, |
| * we just need to specify a number larger than the maximum number of buffers. |
| */ |
| void clean_page_buffers(struct page *page) |
| { |
| clean_buffers(page, ~0U); |
| } |
| |
| static int __mpage_writepage(struct folio *folio, struct writeback_control *wbc, |
| void *data) |
| { |
| struct mpage_data *mpd = data; |
| struct bio *bio = mpd->bio; |
| struct address_space *mapping = folio->mapping; |
| struct inode *inode = mapping->host; |
| const unsigned blkbits = inode->i_blkbits; |
| const unsigned blocks_per_page = PAGE_SIZE >> blkbits; |
| sector_t last_block; |
| sector_t block_in_file; |
| sector_t blocks[MAX_BUF_PER_PAGE]; |
| unsigned page_block; |
| unsigned first_unmapped = blocks_per_page; |
| struct block_device *bdev = NULL; |
| int boundary = 0; |
| sector_t boundary_block = 0; |
| struct block_device *boundary_bdev = NULL; |
| size_t length; |
| struct buffer_head map_bh; |
| loff_t i_size = i_size_read(inode); |
| int ret = 0; |
| struct buffer_head *head = folio_buffers(folio); |
| |
| if (head) { |
| struct buffer_head *bh = head; |
| |
| /* If they're all mapped and dirty, do it */ |
| page_block = 0; |
| do { |
| BUG_ON(buffer_locked(bh)); |
| if (!buffer_mapped(bh)) { |
| /* |
| * unmapped dirty buffers are created by |
| * block_dirty_folio -> mmapped data |
| */ |
| if (buffer_dirty(bh)) |
| goto confused; |
| if (first_unmapped == blocks_per_page) |
| first_unmapped = page_block; |
| continue; |
| } |
| |
| if (first_unmapped != blocks_per_page) |
| goto confused; /* hole -> non-hole */ |
| |
| if (!buffer_dirty(bh) || !buffer_uptodate(bh)) |
| goto confused; |
| if (page_block) { |
| if (bh->b_blocknr != blocks[page_block-1] + 1) |
| goto confused; |
| } |
| blocks[page_block++] = bh->b_blocknr; |
| boundary = buffer_boundary(bh); |
| if (boundary) { |
| boundary_block = bh->b_blocknr; |
| boundary_bdev = bh->b_bdev; |
| } |
| bdev = bh->b_bdev; |
| } while ((bh = bh->b_this_page) != head); |
| |
| if (first_unmapped) |
| goto page_is_mapped; |
| |
| /* |
| * Page has buffers, but they are all unmapped. The page was |
| * created by pagein or read over a hole which was handled by |
| * block_read_full_folio(). If this address_space is also |
| * using mpage_readahead then this can rarely happen. |
| */ |
| goto confused; |
| } |
| |
| /* |
| * The page has no buffers: map it to disk |
| */ |
| BUG_ON(!folio_test_uptodate(folio)); |
| block_in_file = (sector_t)folio->index << (PAGE_SHIFT - blkbits); |
| /* |
| * Whole page beyond EOF? Skip allocating blocks to avoid leaking |
| * space. |
| */ |
| if (block_in_file >= (i_size + (1 << blkbits) - 1) >> blkbits) |
| goto page_is_mapped; |
| last_block = (i_size - 1) >> blkbits; |
| map_bh.b_folio = folio; |
| for (page_block = 0; page_block < blocks_per_page; ) { |
| |
| map_bh.b_state = 0; |
| map_bh.b_size = 1 << blkbits; |
| if (mpd->get_block(inode, block_in_file, &map_bh, 1)) |
| goto confused; |
| if (!buffer_mapped(&map_bh)) |
| goto confused; |
| if (buffer_new(&map_bh)) |
| clean_bdev_bh_alias(&map_bh); |
| if (buffer_boundary(&map_bh)) { |
| boundary_block = map_bh.b_blocknr; |
| boundary_bdev = map_bh.b_bdev; |
| } |
| if (page_block) { |
| if (map_bh.b_blocknr != blocks[page_block-1] + 1) |
| goto confused; |
| } |
| blocks[page_block++] = map_bh.b_blocknr; |
| boundary = buffer_boundary(&map_bh); |
| bdev = map_bh.b_bdev; |
| if (block_in_file == last_block) |
| break; |
| block_in_file++; |
| } |
| BUG_ON(page_block == 0); |
| |
| first_unmapped = page_block; |
| |
| page_is_mapped: |
| /* Don't bother writing beyond EOF, truncate will discard the folio */ |
| if (folio_pos(folio) >= i_size) |
| goto confused; |
| length = folio_size(folio); |
| if (folio_pos(folio) + length > i_size) { |
| /* |
| * The page straddles i_size. It must be zeroed out on each |
| * and every writepage invocation because it may be mmapped. |
| * "A file is mapped in multiples of the page size. For a file |
| * that is not a multiple of the page size, the remaining memory |
| * is zeroed when mapped, and writes to that region are not |
| * written out to the file." |
| */ |
| length = i_size - folio_pos(folio); |
| folio_zero_segment(folio, length, folio_size(folio)); |
| } |
| |
| /* |
| * This page will go to BIO. Do we need to send this BIO off first? |
| */ |
| if (bio && mpd->last_block_in_bio != blocks[0] - 1) |
| bio = mpage_bio_submit(bio); |
| |
| alloc_new: |
| if (bio == NULL) { |
| bio = bio_alloc(bdev, BIO_MAX_VECS, |
| REQ_OP_WRITE | wbc_to_write_flags(wbc), |
| GFP_NOFS); |
| bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9); |
| wbc_init_bio(wbc, bio); |
| } |
| |
| /* |
| * Must try to add the page before marking the buffer clean or |
| * the confused fail path above (OOM) will be very confused when |
| * it finds all bh marked clean (i.e. it will not write anything) |
| */ |
| wbc_account_cgroup_owner(wbc, &folio->page, folio_size(folio)); |
| length = first_unmapped << blkbits; |
| if (!bio_add_folio(bio, folio, length, 0)) { |
| bio = mpage_bio_submit(bio); |
| goto alloc_new; |
| } |
| |
| clean_buffers(&folio->page, first_unmapped); |
| |
| BUG_ON(folio_test_writeback(folio)); |
| folio_start_writeback(folio); |
| folio_unlock(folio); |
| if (boundary || (first_unmapped != blocks_per_page)) { |
| bio = mpage_bio_submit(bio); |
| if (boundary_block) { |
| write_boundary_block(boundary_bdev, |
| boundary_block, 1 << blkbits); |
| } |
| } else { |
| mpd->last_block_in_bio = blocks[blocks_per_page - 1]; |
| } |
| goto out; |
| |
| confused: |
| if (bio) |
| bio = mpage_bio_submit(bio); |
| |
| /* |
| * The caller has a ref on the inode, so *mapping is stable |
| */ |
| ret = block_write_full_page(&folio->page, mpd->get_block, wbc); |
| mapping_set_error(mapping, ret); |
| out: |
| mpd->bio = bio; |
| return ret; |
| } |
| |
| /** |
| * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them |
| * @mapping: address space structure to write |
| * @wbc: subtract the number of written pages from *@wbc->nr_to_write |
| * @get_block: the filesystem's block mapper function. |
| * |
| * This is a library function, which implements the writepages() |
| * address_space_operation. |
| */ |
| int |
| mpage_writepages(struct address_space *mapping, |
| struct writeback_control *wbc, get_block_t get_block) |
| { |
| struct mpage_data mpd = { |
| .get_block = get_block, |
| }; |
| struct blk_plug plug; |
| int ret; |
| |
| blk_start_plug(&plug); |
| ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd); |
| if (mpd.bio) |
| mpage_bio_submit(mpd.bio); |
| blk_finish_plug(&plug); |
| return ret; |
| } |
| EXPORT_SYMBOL(mpage_writepages); |