path: root/block/blk-merge.c
diff options
authorDamien Le Moal <damien.lemoal@wdc.com>2018-11-20 10:52:37 +0900
committerJens Axboe <axboe@kernel.dk>2018-11-19 19:03:49 -0700
commit668ffc03418bc779f699797c72ecf968cd6525a9 (patch)
tree1392526ca5bb0cbe189e7d5ff5d469c51d2ef231 /block/blk-merge.c
parent76dc891395dc61e92e2ff31b6161815ce5eb715b (diff)
block: prevent merging of requests with different priorities
Growing in size a high priority request by merging it with a lower priority BIO or request will increase the request execution time. This is the opposite result of the desired effect of high I/O priorities, namely getting low I/O latencies. Prevent merging of requests and BIOs that have different I/O priorities to fix this. Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-merge.c')
1 files changed, 6 insertions, 2 deletions
diff --git a/block/blk-merge.c b/block/blk-merge.c
index b1df622cbd85..6be04ef8da5b 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -752,6 +752,9 @@ static struct request *attempt_merge(struct request_queue *q,
if (req->write_hint != next->write_hint)
return NULL;
+ if (req->ioprio != next->ioprio)
+ return NULL;
* If we are allowed to merge, then append bio list
* from next to rq and release next. merge_requests_fn
@@ -807,8 +810,6 @@ static struct request *attempt_merge(struct request_queue *q,
- req->ioprio = ioprio_best(req->ioprio, next->ioprio);
* ownership of bio passed from next to req, return 'next' for
* the caller to free
@@ -883,6 +884,9 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
if (rq->write_hint != bio->bi_write_hint)
return false;
+ if (rq->ioprio != bio_prio(bio))
+ return false;
return true;