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blk-mq: special case cached requests less

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Share the main merge / split / integrity preparation code between the
cached request vs newly allocated request cases, and add comments
explaining the cached request handling.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Tested-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20240124092658.2258309-4-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2024-01-24 10:26:58 +01:00 committed by Jens Axboe
parent 337e89feb7
commit 72e84e909e
1 changed files with 22 additions and 19 deletions
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35
block/blk-mq.c
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@ -2967,29 +2967,24 @@ void blk_mq_submit_bio(struct bio *bio)
struct blk_plug *plug = blk_mq_plug(bio);
const int is_sync = op_is_sync(bio->bi_opf);
struct blk_mq_hw_ctx *hctx;
struct request *rq = NULL;
unsigned int nr_segs = 1;
struct request *rq;
blk_status_t ret;
bio = blk_queue_bounce(bio, q);
/*
* If the plug has a cached request for this queue, try use it.
*
* The cached request already holds a q_usage_counter reference and we
* don't have to acquire a new one if we use it.
*/
rq = blk_mq_peek_cached_request(plug, q, bio->bi_opf);
if (rq) {
if (unlikely(bio_may_exceed_limits(bio, &q->limits))) {
bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
if (!bio)
return;
}
if (!bio_integrity_prep(bio))
return;
if (blk_mq_attempt_bio_merge(q, bio, nr_segs))
return;
blk_mq_use_cached_rq(rq, plug, bio);
goto done;
}
if (!rq) {
if (unlikely(bio_queue_enter(bio)))
return;
}
if (unlikely(bio_may_exceed_limits(bio, &q->limits))) {
bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
if (!bio)
@ -3001,11 +2996,14 @@ void blk_mq_submit_bio(struct bio *bio)
if (blk_mq_attempt_bio_merge(q, bio, nr_segs))
goto queue_exit;
if (!rq) {
rq = blk_mq_get_new_requests(q, plug, bio, nr_segs);
if (unlikely(!rq))
goto queue_exit;
} else {
blk_mq_use_cached_rq(rq, plug, bio);
}
done:
trace_block_getrq(bio);
rq_qos_track(q, rq, bio);
@ -3039,6 +3037,11 @@ done:
return;
queue_exit:
/*
* Don't drop the queue reference if we were trying to use a cached
* request and thus didn't acquire one.
*/
if (!rq)
blk_queue_exit(q);
}