[PATCH 1/2] block: Do not merge recursively in elv_attempt_insert_merge()

[Jan Kara <jack@suse.cz>]

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