Re: [PATCH v1 4/6] block: check bio_mergeable() early before merging

[Ming Lei]

On Mon, Oct 19, 2015 at 11:27 PM, Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:
> Ming Lei <ming.lei@xxxxxxxxxxxxx> writes:
>
>> After bio splitting is introduced, one bio can be splitted
>> and it is marked as NOMERGE because it is too fat to be merged,
>> so check bio_mergeable() earlier to avoid to try to merge it
>> unnecessarily.
>>
>> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
>
> Reviewed-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
>
> Ming, do you think we should also add a check in blk_attempt_plug_merge?

No, because 'request_count' need to be figured out for automatic flush plug.

Thanks,

>
> -Jeff
>
>> ---
>>  block/elevator.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/block/elevator.c b/block/elevator.c
>> index 84d6394..c3555c9 100644
>> --- a/block/elevator.c
>> +++ b/block/elevator.c
>> @@ -420,7 +420,7 @@ int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
>>        *      noxmerges: Only simple one-hit cache try
>>        *      merges:    All merge tries attempted
>>        */
>> -     if (blk_queue_nomerges(q))
>> +     if (blk_queue_nomerges(q) || !bio_mergeable(bio))
>>               return ELEVATOR_NO_MERGE;
>>
>>       /*
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