On Mon, Feb 13, 2012 at 05:19:43PM -0500, Martin K. Petersen wrote:
[..]
>
> block: Mark discard requests unmergeable
>
> Discards were globally marked as mergeable and as a result we had
> several code paths that explicitly disabled merging when REQ_DISCARD was
> set.
>
> Mark discard requests as unmergable and remove special-casing of
> REQ_DISCARD.
Mike Snitzer mentioned that we do allow merging of one discard request
with another except following two cases.
- Don't allow merging of secure discard.
- Don't allow merging of discard request with another non-discard request.
I guess that's why DISCARD requests are mergeable globally and later
we deny merge in selected cases. Do we want to disable that behavior?
[..]
> @@ -591,8 +591,7 @@ void __elv_add_request(struct request_queue *q, struct request *rq, int where)
>
> if (rq->cmd_flags & REQ_SOFTBARRIER) {
> /* barriers are scheduling boundary, update end_sector */
> - if (rq->cmd_type == REQ_TYPE_FS ||
> - (rq->cmd_flags & REQ_DISCARD)) {
> + if (rq->cmd_type == REQ_TYPE_FS) {
This is orthogonal to merging?
[..]
> @@ -634,8 +633,7 @@ void __elv_add_request(struct request_queue *q, struct request *rq, int where)
> if (elv_attempt_insert_merge(q, rq))
> break;
> case ELEVATOR_INSERT_SORT:
> - BUG_ON(rq->cmd_type != REQ_TYPE_FS &&
> - !(rq->cmd_flags & REQ_DISCARD));
> + BUG_ON(rq->cmd_type != REQ_TYPE_FS);
This change also looks orthogonal to merging. Will it not trigger BUG_ON()
when DISCARD request is being inserted into the elevator?
Thanks
Vivek
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