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>
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@ -714,6 +714,31 @@ static void blk_account_io_merge(struct request *req)
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part_stat_unlock();
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}
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}
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/*
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* Two cases of handling DISCARD merge:
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* If max_discard_segments > 1, the driver takes every bio
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* as a range and send them to controller together. The ranges
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* needn't to be contiguous.
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* Otherwise, the bios/requests will be handled as same as
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* others which should be contiguous.
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*/
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static inline bool blk_discard_mergable(struct request *req)
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{
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if (req_op(req) == REQ_OP_DISCARD &&
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queue_max_discard_segments(req->q) > 1)
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return true;
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return false;
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}
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enum elv_merge blk_try_req_merge(struct request *req, struct request *next)
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{
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if (blk_discard_mergable(req))
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return ELEVATOR_DISCARD_MERGE;
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else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
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return ELEVATOR_BACK_MERGE;
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return ELEVATOR_NO_MERGE;
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}
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/*
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* For non-mq, this has to be called with the request spinlock acquired.
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@ -731,12 +756,6 @@ static struct request *attempt_merge(struct request_queue *q,
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if (req_op(req) != req_op(next))
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return NULL;
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/*
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* not contiguous
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*/
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if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
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return NULL;
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if (rq_data_dir(req) != rq_data_dir(next)
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|| req->rq_disk != next->rq_disk
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|| req_no_special_merge(next))
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@ -760,11 +779,19 @@ static struct request *attempt_merge(struct request_queue *q,
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* counts here. Handle DISCARDs separately, as they
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* have separate settings.
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*/
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if (req_op(req) == REQ_OP_DISCARD) {
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switch (blk_try_req_merge(req, next)) {
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case ELEVATOR_DISCARD_MERGE:
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if (!req_attempt_discard_merge(q, req, next))
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return NULL;
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} else if (!ll_merge_requests_fn(q, req, next))
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break;
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case ELEVATOR_BACK_MERGE:
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if (!ll_merge_requests_fn(q, req, next))
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return NULL;
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break;
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default:
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return NULL;
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}
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/*
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* If failfast settings disagree or any of the two is already
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@ -888,8 +915,7 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
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enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
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{
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if (req_op(rq) == REQ_OP_DISCARD &&
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queue_max_discard_segments(rq->q) > 1)
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if (blk_discard_mergable(rq))
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return ELEVATOR_DISCARD_MERGE;
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else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
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return ELEVATOR_BACK_MERGE;
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