[PATCH 1/2] block: Do not merge recursively in elv_attempt_insert_merge()
From: Jan Kara <jack@suse.cz>
Date: 2021-05-20 22:34:04
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
Most of the merging happens at bio level. There should not be much merging happening at request level anymore. Furthermore if we backmerged a request to the previous one, the chances to be able to merge the result to even previous request are slim - that could succeed only if requests were inserted in 2 1 3 order. Merging more requests in elv_attempt_insert_merge() will be difficult to handle when we want to pass requests to free back to the caller of blk_mq_sched_try_insert_merge(). So just remove the possibility of merging multiple requests in elv_attempt_insert_merge(). Signed-off-by: Jan Kara <jack@suse.cz> --- block/elevator.c | 19 +++++-------------- 1 file changed, 5 insertions(+), 14 deletions(-)
diff --git a/block/elevator.c b/block/elevator.c
index 440699c28119..098f4bd226f5 100644
--- a/block/elevator.c
+++ b/block/elevator.c@@ -350,12 +350,11 @@ enum elv_merge elv_merge(struct request_queue *q, struct request **req, * we can append 'rq' to an existing request, so we can throw 'rq' away * afterwards. * - * Returns true if we merged, false otherwise + * Returns true if we merged, false otherwise. */ bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq) { struct request *__rq; - bool ret; if (blk_queue_nomerges(q)) return false;
@@ -369,21 +368,13 @@ bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq) if (blk_queue_noxmerges(q)) return false; - ret = false; /* * See if our hash lookup can find a potential backmerge. */ - while (1) { - __rq = elv_rqhash_find(q, blk_rq_pos(rq)); - if (!__rq || !blk_attempt_req_merge(q, __rq, rq)) - break; - - /* The merged request could be merged with others, try again */ - ret = true; - rq = __rq; - } - - return ret; + __rq = elv_rqhash_find(q, blk_rq_pos(rq)); + if (!__rq || !blk_attempt_req_merge(q, __rq, rq)) + return false; + return true; } void elv_merged_request(struct request_queue *q, struct request *rq,
--
2.26.2