Re: [PATCH 3/4] blk-mq: check bio_mergeable() early before merging

[Ming Lei]

On Thu, Oct 15, 2015 at 11:21 PM, Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:
> Ming Lei <ming.lei@xxxxxxxxxxxxx> writes:
>
>> It isn't necessary to try to merge the bio which is marked
>> as NOMERGE.
>>
>> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
>> ---
>>  block/blk-mq.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 546b3b8..deb5f4c 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -671,6 +671,9 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
>>       struct request *rq;
>>       int checked = 8;
>>
>> +     if (!bio_mergeable(bio))
>> +             return false;
>> +
>>       list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
>>               int el_ret;
>>
>> @@ -1140,7 +1143,7 @@ static inline bool blk_mq_merge_queue_io(struct blk_mq_hw_ctx *hctx,
>>                                        struct blk_mq_ctx *ctx,
>>                                        struct request *rq, struct bio *bio)
>>  {
>> -     if (!hctx_allow_merges(hctx)) {
>> +     if (!hctx_allow_merges(hctx) || !bio_mergeable(bio)) {
>>               blk_mq_bio_to_request(rq, bio);
>>               spin_lock(&ctx->lock);
>>  insert_rq:
>
> blk_mq_attempt_merge is only called from blk_mq_merge_queue_io.  So, by
> adding the conditional in blk_mq_merge_queue_io, you don't need any
> change in blk_mq_attempt_merge.

OK.

>
> Also, why haven't you updated the non-multiqueue code paths similarly?

Will do it in v1.

>
> Cheers,
> Jeff
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