[PATCH 4/5] xfs: reduce the number of atomic when locking a buffer after lookup

Christoph Hellwig
2022-04-03T12:01:38Z

From: Dave Chinner <dchinner@redhat.com>

Avoid an extra atomic operation in the non-trylock case by only doing a
trylock if the XBF_TRYLOCK flag is set. This follows the pattern in the
IO path with NOWAIT semantics where the "trylock-fail-lock" path showed
5-10% reduced throughput compared to just using single lock call when not
under NOWAIT conditions. So make that same change here, too.

See commit 942491c9e6d6 ("xfs: fix AIM7 regression") for details.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
[hch: split from a larger patch]
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/xfs/xfs_buf.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index ef645e15935369..dd68aee52118c2 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -636,12 +636,13 @@ xfs_buf_get_map(
}
xfs_perag_put(pag);

- if (!xfs_buf_trylock(bp)) {
- if (flags & XBF_TRYLOCK) {
+ if (flags & XBF_TRYLOCK) {
+ if (!xfs_buf_trylock(bp)) {
xfs_buf_rele(bp);
XFS_STATS_INC(mp, xb_busy_locked);
return -EAGAIN;
}
+ } else {
xfs_buf_lock(bp);
XFS_STATS_INC(mp, xb_get_locked_waited);
}
--
2.30.2