btrfs: simplify inode locking for RWF_NOWAIT

This is similar to 63b45c25c96d ("xfs: fix AIM7 regression"). Apparently
our current rwsem code doesn't like doing the trylock, then lock for
real scheme. This causes extra contention on the lock and can be
measured eg. by AIM7 benchmark.  So change our read/write methods to
just do the trylock for the RWF_NOWAIT case.

Fixes: c41e779b6433 ("btrfs: nowait aio support")
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 435a502a32261071d3bd4ac4e24d75367a349bbb..25ce1b6dbda9dbcd7c13ec820286fdca3ffa6f0d 100644 (file)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1903,9 +1903,10 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
            (iocb->ki_flags & IOCB_NOWAIT))
                return -EOPNOTSUPP;
 
-       if (!inode_trylock(inode)) {
-               if (iocb->ki_flags & IOCB_NOWAIT)
+       if (iocb->ki_flags & IOCB_NOWAIT) {
+               if (!inode_trylock(inode))
                        return -EAGAIN;
+       } else {
                inode_lock(inode);
        }