From: "Yan, Zheng" <zheng.z.yan@xxxxxxxxx>
Our Linux Kernel Performance project found that commit 4e7ea81db5
(ext4: restructure writeback path) indroduced a read performance
regression. After the commit, ext4 does not merge adjacent delayed
pages during writeback. The regression is caused by the "buffer
mapped" check in mpage_add_bh_to_extent(), delayed dirty pages are
not mapped.
Signed-off-by: Yan, Zheng <zheng.z.yan@xxxxxxxxx>
---
fs/ext4/inode.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c79fd7d..f2034cb 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1944,8 +1944,9 @@ static bool mpage_add_bh_to_extent(struct mpage_da_data *mpd, ext4_lblk_t lblk,
struct ext4_map_blocks *map = &mpd->map;
/* Buffer that doesn't need mapping for writeback? */
- if (!buffer_dirty(bh) || !buffer_mapped(bh) ||
- (!buffer_delay(bh) && !buffer_unwritten(bh))) {
+ if (!buffer_dirty(bh) ||
+ (!buffer_mapped(bh) &&
+ !buffer_delay(bh) && !buffer_unwritten(bh))) {
/* So far no extent to map => we write the buffer right away */
if (map->m_len == 0)
return true;
--
1.8.1.4
--
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