There are two cases when handle DISCARD merge - max_discard_segments == 1 bios need to be contiguous - max_discard_segments > 1 Only nvme right now. 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. Signed-off-by: Jianchao Wang <[email protected]> --- V2: - Add max_discard_segments > 1 checking in attempt_merge - Change patch title and comment - Add more comment in attempt_merge block/blk-merge.c | 24 +++++++++++++++++++----- 1 file changed, 19 insertions(+), 5 deletions(-) diff --git a/block/blk-merge.c b/block/blk-merge.c index 42a4674..8f22374 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -734,8 +734,15 @@ static struct request *attempt_merge(struct request_queue *q, /* * not contiguous */ - if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)) - return NULL; + if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)) { + /* + * When max_discard_segments is bigger than 1 (only nvme right + * now), needn't consider the contiguity. + */ + if (!(req_op(req) == REQ_OP_DISCARD && + queue_max_discard_segments(q) > 1)) + return NULL; + } if (rq_data_dir(req) != rq_data_dir(next) || req->rq_disk != next->rq_disk @@ -757,10 +764,17 @@ static struct request *attempt_merge(struct request_queue *q, * If we are allowed to merge, then append bio list * from next to rq and release next. merge_requests_fn * will have updated segment counts, update sector - * counts here. Handle DISCARDs separately, as they - * have separate settings. + * counts here. + * Two cases of Handling DISCARD: + * - max_discard_segments == 1 + * The bios need to be contiguous. + * - max_discard_segments > 1 + * Only nvme right now. It takes every bio as a + * range and send them to controller together. The ranges + * needn't to be contiguous. */ - if (req_op(req) == REQ_OP_DISCARD) { + if (req_op(req) == REQ_OP_DISCARD && + queue_max_discard_segments(q) > 1) { if (!req_attempt_discard_merge(q, req, next)) return NULL; } else if (!ll_merge_requests_fn(q, req, next)) -- 2.7.4
