On 1/16/21 2:15 AM, Qu Wenruo wrote:
Introduce a new helper, read_extent_buffer_subpage(), to do the subpage extent buffer read.The difference between regular and subpage routines are: - No page locking Here we completely rely on extent locking. Page locking can reduce the concurrency greatly, as if we lock one page to read one extent buffer, all the other extent buffers in the same page will have to wait. - Extent uptodate condition Despite the existing PageUptodate() and EXTENT_BUFFER_UPTODATE check, We also need to check btrfs_subpage::uptodate_bitmap. - No page loop Just one page, no need to loop, this greately simplified the subpage routine. This patch only implemented the bio submit part, no endio support yet. Signed-off-by: Qu Wenruo <w...@suse.com> --- fs/btrfs/extent_io.c | 70 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 70 insertions(+) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 9414219fa28b..291ff76d5b2e 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -5718,6 +5718,73 @@ void set_extent_buffer_uptodate(struct extent_buffer *eb) } }+static int read_extent_buffer_subpage(struct extent_buffer *eb, int wait,+ int mirror_num) +{ + struct btrfs_fs_info *fs_info = eb->fs_info; + struct extent_io_tree *io_tree; + struct page *page = eb->pages[0]; + struct bio *bio = NULL; + int ret = 0; + + ASSERT(!test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags)); + ASSERT(PagePrivate(page)); + io_tree = &BTRFS_I(fs_info->btree_inode)->io_tree; + + if (wait == WAIT_NONE) { + ret = try_lock_extent(io_tree, eb->start, + eb->start + eb->len - 1); + if (ret <= 0) + return ret; + } else { + ret = lock_extent(io_tree, eb->start, eb->start + eb->len - 1); + if (ret < 0) + return ret; + } + + ret = 0; + if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags) || + PageUptodate(page) || + btrfs_subpage_test_uptodate(fs_info, page, eb->start, eb->len)) { + set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags); + unlock_extent(io_tree, eb->start, eb->start + eb->len - 1); + return ret; + } + + clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags); + eb->read_mirror = 0; + atomic_set(&eb->io_pages, 1); + check_buffer_tree_ref(eb);
We need btrfs_subpage_clear_error() here as well. Thanks, Josef
