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authorJens Axboe <axboe@kernel.dk>2022-03-11 10:21:43 -0700
committerJens Axboe <axboe@kernel.dk>2022-03-11 11:08:21 -0700
commit5b2050718d095cd3242d1f42aaaea3a2fec8e6f0 (patch)
tree43433e92bb2218962ec85c17df2c2ba8b093aebf /block
parent5ca7546fe317bd181ad55f623f6e522069c2e426 (diff)
block: ensure plug merging checks the correct queue at least once
Song reports that a RAID rebuild workload runs much slower recently, and it is seeing a lot less merging than it did previously. The reason is that a previous commit reduced the amount of work we do for plug merging. RAID rebuild interleaves requests between disks, so a last-entry check in plug merging always misses a merge opportunity since we always find a different disk than what we are looking for. Modify the logic such that it's still a one-hit cache, but ensure that we check enough to find the right target before giving up. Fixes: d38a9c04c0d5 ("block: only check previous entry for plug merge attempt") Reported-and-tested-by: Song Liu <song@kernel.org> Reviewed-by: Song Liu <songliubraving@fb.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
-rw-r--r--block/blk-merge.c20
1 files changed, 14 insertions, 6 deletions
diff --git a/block/blk-merge.c b/block/blk-merge.c
index f5255991b773..8d8177f71ebd 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -1087,12 +1087,20 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
if (!plug || rq_list_empty(plug->mq_list))
return false;
- /* check the previously added entry for a quick merge attempt */
- rq = rq_list_peek(&plug->mq_list);
- if (rq->q == q) {
- if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) ==
- BIO_MERGE_OK)
- return true;
+ rq_list_for_each(&plug->mq_list, rq) {
+ if (rq->q == q) {
+ if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) ==
+ BIO_MERGE_OK)
+ return true;
+ break;
+ }
+
+ /*
+ * Only keep iterating plug list for merges if we have multiple
+ * queues
+ */
+ if (!plug->multiple_queues)
+ break;
}
return false;
}