btrfs: use per-buffer locking for extent_buffer reading
Instead of locking and unlocking every page or the extent, just add a new EXTENT_BUFFER_READING bit that mirrors EXTENT_BUFFER_WRITEBACK for synchronizing threads trying to read an extent_buffer and to wait for I/O completion. Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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@ -4049,6 +4049,7 @@ void set_extent_buffer_uptodate(struct extent_buffer *eb)
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static void extent_buffer_read_end_io(struct btrfs_bio *bbio)
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{
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struct extent_buffer *eb = bbio->private;
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struct btrfs_fs_info *fs_info = eb->fs_info;
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bool uptodate = !bbio->bio.bi_status;
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struct bvec_iter_all iter_all;
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struct bio_vec *bvec;
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@ -4068,26 +4069,47 @@ static void extent_buffer_read_end_io(struct btrfs_bio *bbio)
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}
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bio_for_each_segment_all(bvec, &bbio->bio, iter_all) {
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end_page_read(bvec->bv_page, uptodate, eb->start + bio_offset,
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bvec->bv_len);
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bio_offset += bvec->bv_len;
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u64 start = eb->start + bio_offset;
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struct page *page = bvec->bv_page;
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u32 len = bvec->bv_len;
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if (uptodate)
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btrfs_page_set_uptodate(fs_info, page, start, len);
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else
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btrfs_page_clear_uptodate(fs_info, page, start, len);
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bio_offset += len;
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}
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if (eb->fs_info->nodesize < PAGE_SIZE) {
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unlock_extent(&bbio->inode->io_tree, eb->start,
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eb->start + bio_offset - 1, NULL);
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}
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clear_bit(EXTENT_BUFFER_READING, &eb->bflags);
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smp_mb__after_atomic();
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wake_up_bit(&eb->bflags, EXTENT_BUFFER_READING);
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free_extent_buffer(eb);
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bio_put(&bbio->bio);
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}
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static void __read_extent_buffer_pages(struct extent_buffer *eb, int mirror_num,
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struct btrfs_tree_parent_check *check)
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int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num,
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struct btrfs_tree_parent_check *check)
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{
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int num_pages = num_extent_pages(eb), i;
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struct btrfs_bio *bbio;
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if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
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return 0;
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/*
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* We could have had EXTENT_BUFFER_UPTODATE cleared by the write
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* operation, which could potentially still be in flight. In this case
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* we simply want to return an error.
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*/
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if (unlikely(test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)))
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return -EIO;
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/* Someone else is already reading the buffer, just wait for it. */
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if (test_and_set_bit(EXTENT_BUFFER_READING, &eb->bflags))
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goto done;
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clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
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eb->read_mirror = 0;
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check_buffer_tree_ref(eb);
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@ -4108,117 +4130,15 @@ static void __read_extent_buffer_pages(struct extent_buffer *eb, int mirror_num,
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__bio_add_page(&bbio->bio, eb->pages[i], PAGE_SIZE, 0);
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}
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btrfs_submit_bio(bbio, mirror_num);
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}
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static int read_extent_buffer_subpage(struct extent_buffer *eb, int wait,
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int mirror_num,
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struct btrfs_tree_parent_check *check)
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{
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struct btrfs_fs_info *fs_info = eb->fs_info;
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struct extent_io_tree *io_tree;
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struct page *page = eb->pages[0];
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struct extent_state *cached_state = NULL;
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int ret;
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ASSERT(!test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags));
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ASSERT(PagePrivate(page));
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ASSERT(check);
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io_tree = &BTRFS_I(fs_info->btree_inode)->io_tree;
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if (wait == WAIT_NONE) {
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if (!try_lock_extent(io_tree, eb->start, eb->start + eb->len - 1,
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&cached_state))
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return -EAGAIN;
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} else {
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ret = lock_extent(io_tree, eb->start, eb->start + eb->len - 1,
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&cached_state);
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if (ret < 0)
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return ret;
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}
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if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags)) {
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unlock_extent(io_tree, eb->start, eb->start + eb->len - 1,
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&cached_state);
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return 0;
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}
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btrfs_subpage_start_reader(fs_info, page, eb->start, eb->len);
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__read_extent_buffer_pages(eb, mirror_num, check);
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if (wait != WAIT_COMPLETE) {
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free_extent_state(cached_state);
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return 0;
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}
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wait_extent_bit(io_tree, eb->start, eb->start + eb->len - 1,
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EXTENT_LOCKED, &cached_state);
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if (!test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
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return -EIO;
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return 0;
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}
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int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num,
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struct btrfs_tree_parent_check *check)
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{
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int i;
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struct page *page;
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int locked_pages = 0;
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int num_pages;
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if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
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return 0;
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/*
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* We could have had EXTENT_BUFFER_UPTODATE cleared by the write
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* operation, which could potentially still be in flight. In this case
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* we simply want to return an error.
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*/
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if (unlikely(test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)))
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return -EIO;
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if (eb->fs_info->nodesize < PAGE_SIZE)
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return read_extent_buffer_subpage(eb, wait, mirror_num, check);
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num_pages = num_extent_pages(eb);
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for (i = 0; i < num_pages; i++) {
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page = eb->pages[i];
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if (wait == WAIT_NONE) {
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/*
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* WAIT_NONE is only utilized by readahead. If we can't
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* acquire the lock atomically it means either the eb
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* is being read out or under modification.
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* Either way the eb will be or has been cached,
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* readahead can exit safely.
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*/
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if (!trylock_page(page))
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goto unlock_exit;
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} else {
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lock_page(page);
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}
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locked_pages++;
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}
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__read_extent_buffer_pages(eb, mirror_num, check);
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if (wait != WAIT_COMPLETE)
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return 0;
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for (i = 0; i < num_pages; i++) {
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page = eb->pages[i];
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wait_on_page_locked(page);
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if (!PageUptodate(page))
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done:
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if (wait == WAIT_COMPLETE) {
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wait_on_bit_io(&eb->bflags, EXTENT_BUFFER_READING, TASK_UNINTERRUPTIBLE);
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if (!test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
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return -EIO;
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}
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return 0;
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unlock_exit:
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while (locked_pages > 0) {
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locked_pages--;
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page = eb->pages[locked_pages];
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unlock_page(page);
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}
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return 0;
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}
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static bool report_eb_range(const struct extent_buffer *eb, unsigned long start,
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@ -29,6 +29,8 @@ enum {
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/* write IO error */
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EXTENT_BUFFER_WRITE_ERR,
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EXTENT_BUFFER_NO_CHECK,
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/* Indicate that extent buffer pages a being read */
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EXTENT_BUFFER_READING,
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};
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/* these are flags for __process_pages_contig */
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