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-rw-r--r--fs/mpage.c685
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diff --git a/fs/mpage.c b/fs/mpage.c
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+// 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_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) {
+ if (err)
+ folio_set_error(fi.folio);
+ else
+ folio_mark_uptodate(fi.folio);
+ folio_unlock(fi.folio);
+ }
+
+ 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) {
+ folio_set_error(fi.folio);
+ 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 == 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_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 = blocks[0] << (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_page))
+ args->bio = mpage_bio_submit_read(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_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);
+ args.bio = do_mpage_readpage(&args);
+ }
+ 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 = 1,
+ .get_block = get_block,
+ };
+
+ args.bio = 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 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_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 = 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_write(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_write(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_write(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_write(mpd.bio);
+ blk_finish_plug(&plug);
+ return ret;
+}
+EXPORT_SYMBOL(mpage_writepages);
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-14 18:04:30 +0000