btrfs: simplify inode locking for RWF_NOWAIT

BugLink: https://bugs.launchpad.net/bugs/1861934
commit 9cf35f673583ccc9f3e2507498b3079d56614ad3 upstream.

This is similar to 942491c9e6d6 ("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: edf064e7c6fe ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 4f54b40d11f57cc25a2e669be491f1dc91be3ec1..8abb00d215627be3d22125f45a2f2f7096ecb743 100644 (file)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1920,9 +1920,10 @@ 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);
        }