From: Christoph Hellwig hch@lst.de
[ Upstream commit e95382834cf885b478dbe14a66451b863eb35c94 ]
Currently read_extent_buffer_pages skips pages that are already uptodate when reading in an extent_buffer. While this reduces the amount of data read, it increases the number of I/O operations as we now need to do multiple I/Os when reading an extent buffer with one or more uptodate pages in the middle of it. On any modern storage device, be that hard drives or SSDs this actually decreases I/O performance. Fortunately this case is pretty rare as the pages are always initially read together and then aged the same way. Besides simplifying the code a bit as-is this will allow for major simplifications to the I/O completion handler later on.
Note that the case where all pages are uptodate is still handled by an optimized fast path that does not read any data from disk.
Reviewed-by: Johannes Thumshirn johannes.thumshirn@wdc.com Reviewed-by: Qu Wenruo wqu@suse.com Signed-off-by: Christoph Hellwig hch@lst.de Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Stable-dep-of: 7027f87108ce ("btrfs: don't treat zoned writeback as being from an async helper thread") Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/extent_io.c | 17 +++++------------ 1 file changed, 5 insertions(+), 12 deletions(-)
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index a1adadd5d25dd..d1a635f237688 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -4314,7 +4314,6 @@ int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num, int locked_pages = 0; int all_uptodate = 1; int num_pages; - unsigned long num_reads = 0; struct btrfs_bio_ctrl bio_ctrl = { .opf = REQ_OP_READ, .mirror_num = mirror_num, @@ -4360,10 +4359,8 @@ int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num, */ for (i = 0; i < num_pages; i++) { page = eb->pages[i]; - if (!PageUptodate(page)) { - num_reads++; + if (!PageUptodate(page)) all_uptodate = 0; - } }
if (all_uptodate) { @@ -4373,7 +4370,7 @@ int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num,
clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags); eb->read_mirror = 0; - atomic_set(&eb->io_pages, num_reads); + atomic_set(&eb->io_pages, num_pages); /* * It is possible for release_folio to clear the TREE_REF bit before we * set io_pages. See check_buffer_tree_ref for a more detailed comment. @@ -4383,13 +4380,9 @@ int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num, for (i = 0; i < num_pages; i++) { page = eb->pages[i];
- if (!PageUptodate(page)) { - ClearPageError(page); - submit_extent_page(&bio_ctrl, page_offset(page), page, - PAGE_SIZE, 0); - } else { - unlock_page(page); - } + ClearPageError(page); + submit_extent_page(&bio_ctrl, page_offset(page), page, + PAGE_SIZE, 0); }
submit_one_bio(&bio_ctrl);