Currently on the slow path insert we repeat the initial hash table lookup before we attempt the insert, resulting in a two traversals of the hash table to ensure the insert is valid. The rhashtable API provides a method for an atomic lookup and insert operation, so we can avoid one of the hash table traversals by using this method. Adapted from a large patch containing this optimisation by Christoph Hellwig. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Darrick J. Wong <djwong@kernel.org>