On 10/22/18 5:00 PM, Christoph Hellwig wrote:
> On Sat, Oct 20, 2018 at 10:29:37PM +0800, Jianchao Wang wrote:
>> 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;
>
> Why not:
>
> if (req_op(req) != REQ_OP_DISCARD ||
> queue_max_discard_segments(q) == 1)>
> which would be a lot more obvious?
OK, I will change it
>
>> + * 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.
>
> The formatting looks odd. Also I don't think we should mention the
> users here, as others might grow (virtio is in the pipe, SCSI could
> be supported easily if someone did the work).
>
Yes, I will change the format and discard the users here.
Thanks
Jianchao
