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blk-mq: cleanup request allocation

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Refactor the request alloction so that blk_mq_get_cached_request tries
to find a cached request first, and the entirely separate and now
self contained blk_mq_get_new_requests allocates one or more requests
if that is not possible.

There is a small change in behavior as submit_bio_checks is called
twice now if a cached request is present but can't be used, but that
is a small price to pay for unwinding this code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20211124062856.1444266-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2021-11-24 07:28:56 +01:00 committed by Jens Axboe
parent 82d981d423
commit 5b13bc8a3f
1 changed files with 44 additions and 58 deletions
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68
block/blk-mq.c
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@ -2717,8 +2717,12 @@ static struct request *blk_mq_get_new_requests(struct request_queue *q,
};
struct request *rq;
if (blk_mq_attempt_bio_merge(q, bio, nsegs))
if (unlikely(bio_queue_enter(bio)))
return NULL;
if (unlikely(!submit_bio_checks(bio)))
goto queue_exit;
if (blk_mq_attempt_bio_merge(q, bio, nsegs))
goto queue_exit;
rq_qos_throttle(q, bio);
@ -2729,64 +2733,44 @@ static struct request *blk_mq_get_new_requests(struct request_queue *q,
}
rq = __blk_mq_alloc_requests(&data);
if (rq)
if (!rq)
goto fail;
return rq;
fail:
rq_qos_cleanup(q, bio);
if (bio->bi_opf & REQ_NOWAIT)
bio_wouldblock_error(bio);
queue_exit:
blk_queue_exit(q);
return NULL;
}
static inline bool blk_mq_can_use_cached_rq(struct request *rq, struct bio *bio)
{
if (blk_mq_get_hctx_type(bio->bi_opf) != rq->mq_hctx->type)
return false;
if (op_is_flush(rq->cmd_flags) != op_is_flush(bio->bi_opf))
return false;
return true;
}
static inline struct request *blk_mq_get_request(struct request_queue *q,
struct blk_plug *plug,
struct bio *bio,
unsigned int nsegs)
static inline struct request *blk_mq_get_cached_request(struct request_queue *q,
struct blk_plug *plug, struct bio *bio, unsigned int nsegs)
{
struct request *rq;
bool checked = false;
if (plug) {
if (!plug)
return NULL;
rq = rq_list_peek(&plug->cached_rq);
if (rq && rq->q == q) {
if (!rq || rq->q != q)
return NULL;
if (unlikely(!submit_bio_checks(bio)))
return NULL;
if (blk_mq_attempt_bio_merge(q, bio, nsegs))
return NULL;
checked = true;
if (!blk_mq_can_use_cached_rq(rq, bio))
goto fallback;
if (blk_mq_get_hctx_type(bio->bi_opf) != rq->mq_hctx->type)
return NULL;
if (op_is_flush(rq->cmd_flags) != op_is_flush(bio->bi_opf))
return NULL;
rq->cmd_flags = bio->bi_opf;
plug->cached_rq = rq_list_next(rq);
INIT_LIST_HEAD(&rq->queuelist);
rq_qos_throttle(q, bio);
return rq;
}
}
fallback:
if (unlikely(bio_queue_enter(bio)))
return NULL;
if (unlikely(!checked && !submit_bio_checks(bio)))
goto out_put;
rq = blk_mq_get_new_requests(q, plug, bio, nsegs);
if (rq)
return rq;
out_put:
blk_queue_exit(q);
return NULL;
}
/**
@ -2805,9 +2789,9 @@ out_put:
void blk_mq_submit_bio(struct bio *bio)
{
struct request_queue *q = bdev_get_queue(bio->bi_bdev);
struct blk_plug *plug = blk_mq_plug(q, bio);
const int is_sync = op_is_sync(bio->bi_opf);
struct request *rq;
struct blk_plug *plug;
unsigned int nr_segs = 1;
blk_status_t ret;
@ -2821,10 +2805,12 @@ void blk_mq_submit_bio(struct bio *bio)
if (!bio_integrity_prep(bio))
return;
plug = blk_mq_plug(q, bio);
rq = blk_mq_get_request(q, plug, bio, nr_segs);
rq = blk_mq_get_cached_request(q, plug, bio, nr_segs);
if (!rq) {
rq = blk_mq_get_new_requests(q, plug, bio, nr_segs);
if (unlikely(!rq))
return;
}
trace_block_getrq(bio);