Commit 69840466 authored by Jianchao Wang's avatar Jianchao Wang Committed by Jens Axboe
Browse files

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: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJianchao Wang <jianchao.w.wang@oracle.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent a435ab4f

block/blk-merge.c

+36 −10
Original line number Diff line number Diff line
@@ -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;

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