Instead of a convoluted chain just check for REQ_OP_READ directly,
and keep all the memory stall code together in a single unlikely
branch.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>