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block: fix the DISCARD request merge 

There are two cases when handle DISCARD merge.
If max_discard_segments == 1, the bios/requests need to be contiguous
to merge. If max_discard_segments > 1, it takes every bio as a range
and different range needn't to be contiguous.

But now, attempt_merge screws this up. It always consider contiguity
for DISCARD for the case max_discard_segments > 1 and cannot merge
contiguous DISCARD for the case max_discard_segments == 1, because
rq_attempt_discard_merge always returns false in this case.
This patch fixes both of the two cases above.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jianchao Wang 2018-10-27 19:52:14 +08:00 committed by Jens Axboe
parent a435ab4f80
commit 6984046608
1 changed files with 36 additions and 10 deletions
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46
block/blk-merge.c
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@ -714,6 +714,31 @@ static void blk_account_io_merge(struct request *req)
part_stat_unlock();
}
}
/*
* Two cases of handling DISCARD merge:
* If max_discard_segments > 1, the driver takes every bio
* as a range and send them to controller together. The ranges
* needn't to be contiguous.
* Otherwise, the bios/requests will be handled as same as
* others which should be contiguous.
*/
static inline bool blk_discard_mergable(struct request *req)
{
if (req_op(req) == REQ_OP_DISCARD &&
queue_max_discard_segments(req->q) > 1)
return true;
return false;
}
enum elv_merge blk_try_req_merge(struct request *req, struct request *next)
{
if (blk_discard_mergable(req))
return ELEVATOR_DISCARD_MERGE;
else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
return ELEVATOR_BACK_MERGE;
return ELEVATOR_NO_MERGE;
}
/*
* For non-mq, this has to be called with the request spinlock acquired.
@ -731,12 +756,6 @@ static struct request *attempt_merge(struct request_queue *q,
if (req_op(req) != req_op(next))
return NULL;
/*
* not contiguous
*/
if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
return NULL;
if (rq_data_dir(req) != rq_data_dir(next)
|| req->rq_disk != next->rq_disk
|| req_no_special_merge(next))
@ -760,11 +779,19 @@ static struct request *attempt_merge(struct request_queue *q,
* counts here. Handle DISCARDs separately, as they
* have separate settings.
*/
if (req_op(req) == REQ_OP_DISCARD) {
switch (blk_try_req_merge(req, next)) {
case ELEVATOR_DISCARD_MERGE:
if (!req_attempt_discard_merge(q, req, next))
return NULL;
} else if (!ll_merge_requests_fn(q, req, next))
break;
case ELEVATOR_BACK_MERGE:
if (!ll_merge_requests_fn(q, req, next))
return NULL;
break;
default:
return NULL;
}
/*
* If failfast settings disagree or any of the two is already
@ -888,8 +915,7 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
{
if (req_op(rq) == REQ_OP_DISCARD &&
queue_max_discard_segments(rq->q) > 1)
if (blk_discard_mergable(rq))
return ELEVATOR_DISCARD_MERGE;
else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
return ELEVATOR_BACK_MERGE;