Re: WARNING: CPU: 2 PID: 207 at drivers/nvme/host/core.c:527 nvme_setup_cmd+0x3d3
From: Jens Axboe <axboe@kernel.dk>
Date: 2018-02-01 15:26:11
Also in:
linux-nvme
On 1/31/18 9:56 PM, Keith Busch wrote:
On Wed, Jan 31, 2018 at 08:07:41PM -0700, Jens Axboe wrote:quoted
if (total_phys_segments > queue_max_segments(q)) - return 0; + return 0;This perhaps unintended change happens to point out another problem: queue_max_segments is the wrong limit for discards, which require queue_max_discard_segments. It might be easier to merge discard requests special, like how merging a discard bio is handled (untested).
Yeah agreed, we should just split it up completely instead instead of special casing it in the read/write path.
quoted hunk ↗ jump to hunk
diff --git a/block/blk-merge.c b/block/blk-merge.c index 8452fc7164cc..01671e1373ff 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c@@ -550,6 +550,28 @@ static bool req_no_special_merge(struct request *req) return !q->mq_ops && req->special; } +static bool req_attempt_discard_merge(struct request_queue *q, struct request *req, + struct request *next) +{ + unsigned short segments = blk_rq_nr_discard_segments(req); + + if (segments >= queue_max_discard_segments(q)) + goto no_merge; + if (blk_rq_sectors(req) + bio_sectors(next->bio) > + blk_rq_get_max_sectors(req, blk_rq_pos(req))) + goto no_merge; + + req->biotail->bi_next = next->bio; + req->biotail = next->biotail; + req->nr_phys_segments = segments + blk_rq_nr_discard_segments(next); + next->bio = NULL; + return true; + +no_merge: + req_set_nomerge(q, req); + return false; +} + static int ll_merge_requests_fn(struct request_queue *q, struct request *req, struct request *next) {@@ -679,6 +701,15 @@ static struct request *attempt_merge(struct request_queue *q, if (req->write_hint != next->write_hint) return NULL; + /* + * Discards are ... special. + */ + if (req_op(req) == REQ_OP_DISCARD) { + if (req_attempt_discard_merge(q, req, next)) + return next; + return NULL; + } + /* * If we are allowed to merge, then append bio list * from next to rq and release next. merge_requests_fn
This looks fine to me, the bio-to-request merge path already looks correct. Care to send a properly formatted patch? -- Jens Axboe