[PATCH] Only the first two bits in bio->bi_rw and rq->flags match

Not three, as assumed. This causes the barrier bit to be needlessly set
for some IO.
Signed-off-by: Jens Axboe <axboe@suse.de>

block/ll_rw_blk.c

@@ -3491,8 +3491,8 @@ EXPORT_SYMBOL(end_request);
 
 void blk_rq_bio_prep(request_queue_t *q, struct request *rq, struct bio *bio)
 {
-	/* first three bits are identical in rq->flags and bio->bi_rw */
-	rq->flags |= (bio->bi_rw & 7);
+	/* first two bits are identical in rq->flags and bio->bi_rw */
+	rq->flags |= (bio->bi_rw & 3);
 
 	rq->nr_phys_segments = bio_phys_segments(q, bio);
 	rq->nr_hw_segments = bio_hw_segments(q, bio);

include/linux/blktrace_api.h

@@ -148,7 +148,7 @@ static inline void blk_add_trace_rq(struct request_queue *q, struct request *rq,
 				    u32 what)
 {
 	struct blk_trace *bt = q->blk_trace;
-	int rw = rq->flags & 0x07;
+	int rw = rq->flags & 0x03;
 
 	if (likely(!bt))
 		return;