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 <jianchao.w.wang@xxxxxxxxxx>
---
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
