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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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#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 "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_read_end_io(struct bio *bio){ struct folio_iter fi; int err = blk_status_to_errno(bio->bi_status);
bio_for_each_folio_all(fi, bio) folio_end_read(fi.folio, err == 0);
bio_put(bio);}
static void mpage_write_end_io(struct bio *bio){ struct folio_iter fi; int err = blk_status_to_errno(bio->bi_status);
bio_for_each_folio_all(fi, bio) { if (err) mapping_set_error(fi.folio->mapping, err); folio_end_writeback(fi.folio); }
bio_put(bio);}
static struct bio *mpage_bio_submit_read(struct bio *bio){ bio->bi_end_io = mpage_read_end_io; guard_bio_eod(bio); submit_bio(bio); return NULL;}
static struct bio *mpage_bio_submit_write(struct bio *bio){ bio->bi_end_io = mpage_write_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 == folio_shift(folio) && buffer_uptodate(bh)) { folio_mark_uptodate(folio); return; } head = create_empty_buffers(folio, i_blocksize(inode), 0); }
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 void 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_folio = folio_size(folio) >> 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 first_block; unsigned page_block; unsigned first_hole = blocks_per_folio; 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);
if (args->is_readahead) { opf |= REQ_RAHEAD; gfp |= __GFP_NORETRY | __GFP_NOWARN; }
if (folio_buffers(folio)) goto confused;
block_in_file = folio_pos(folio) >> blkbits; last_block = block_in_file + ((args->nr_pages * PAGE_SIZE) >> blkbits); 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;
first_block = map_bh->b_blocknr + map_offset; for (relative_block = 0; ; relative_block++) { if (relative_block == last) { clear_buffer_mapped(map_bh); break; } if (page_block == blocks_per_folio) break; 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_folio) { 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_folio) 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_folio) goto confused; /* hole -> non-hole */
/* Contiguous blocks? */ if (!page_block) first_block = map_bh->b_blocknr; else if (first_block + page_block != map_bh->b_blocknr) 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_folio) break; page_block++; block_in_file++; } bdev = map_bh->b_bdev; }
if (first_hole != blocks_per_folio) { folio_zero_segment(folio, first_hole << blkbits, folio_size(folio)); 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 != first_block - 1)) args->bio = mpage_bio_submit_read(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 = first_block << (blkbits - 9); }
length = first_hole << blkbits; if (!bio_add_folio(args->bio, folio, length, 0)) { args->bio = mpage_bio_submit_read(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_folio)) args->bio = mpage_bio_submit_read(args->bio); else args->last_block_in_bio = first_block + blocks_per_folio - 1;out: return;
confused: if (args->bio) args->bio = mpage_bio_submit_read(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); do_mpage_readpage(&args); /* * If read ahead failed synchronously, it may cause by removed * device, or some filesystem metadata error. */ if (!folio_test_locked(folio) && !folio_test_uptodate(folio)) break; } if (args.bio) mpage_bio_submit_read(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 = folio_nr_pages(folio), .get_block = get_block, };
do_mpage_readpage(&args); if (args.bio) mpage_bio_submit_read(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 folio *folio, unsigned first_unmapped){ unsigned buffer_counter = 0; struct buffer_head *bh, *head = folio_buffers(folio);
if (!head) return; 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 && folio_test_uptodate(folio)) try_to_free_buffers(folio);}
static int mpage_write_folio(struct writeback_control *wbc, struct folio *folio, struct mpage_data *mpd){ 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_folio = folio_size(folio) >> blkbits; sector_t last_block; sector_t block_in_file; sector_t first_block; unsigned page_block; unsigned first_unmapped = blocks_per_folio; 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_folio) first_unmapped = page_block; continue; }
if (first_unmapped != blocks_per_folio) goto confused; /* hole -> non-hole */
if (!buffer_dirty(bh) || !buffer_uptodate(bh)) goto confused; if (page_block) { if (bh->b_blocknr != first_block + page_block) goto confused; } else { first_block = bh->b_blocknr; } page_block++; 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 = folio_pos(folio) >> 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_folio; ) {
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 != first_block + page_block) goto confused; } else { first_block = map_bh.b_blocknr; } page_block++; 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 != first_block - 1) bio = mpage_bio_submit_write(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 = first_block << (blkbits - 9); wbc_init_bio(wbc, bio); bio->bi_write_hint = inode->i_write_hint; }
/* * 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, folio_size(folio)); length = first_unmapped << blkbits; if (!bio_add_folio(bio, folio, length, 0)) { bio = mpage_bio_submit_write(bio); goto alloc_new; }
clean_buffers(folio, first_unmapped);
BUG_ON(folio_test_writeback(folio)); folio_start_writeback(folio); folio_unlock(folio); if (boundary || (first_unmapped != blocks_per_folio)) { bio = mpage_bio_submit_write(bio); if (boundary_block) { write_boundary_block(boundary_bdev, boundary_block, 1 << blkbits); } } else { mpd->last_block_in_bio = first_block + blocks_per_folio - 1; } goto out;
confused: if (bio) bio = mpage_bio_submit_write(bio);
/* * The caller has a ref on the inode, so *mapping is stable */ ret = block_write_full_folio(folio, wbc, mpd->get_block); 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. * @write_folio: handler to call for each folio before calling * mpage_write_folio() * * This is a library function, which implements the writepages() * address_space_operation. It calls @write_folio handler for each folio. If * the handler returns value > 0, it calls mpage_write_folio() to do the * folio writeback. */int__mpage_writepages(struct address_space *mapping, struct writeback_control *wbc, get_block_t get_block, int (*write_folio)(struct folio *folio, struct writeback_control *wbc)){ struct mpage_data mpd = { .get_block = get_block, }; struct folio *folio = NULL; struct blk_plug plug; int error;
blk_start_plug(&plug); while ((folio = writeback_iter(mapping, wbc, folio, &error))) { if (write_folio) { error = write_folio(folio, wbc); /* * == 0 means folio is handled, < 0 means error. In * both cases hand back control to writeback_iter() */ if (error <= 0) continue; /* Let mpage_write_folio() handle the folio. */ } error = mpage_write_folio(wbc, folio, &mpd); } if (mpd.bio) mpage_bio_submit_write(mpd.bio); blk_finish_plug(&plug); return error;}EXPORT_SYMBOL(__mpage_writepages);