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

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On Thu, Oct 15, 2015 at 11:21 PM, Jeff Moyer <jmoyer@redhat.com> wrote:
> Ming Lei <ming.lei@canonical.com> writes:
>
>> It isn't necessary to try to merge the bio which is marked
>> as NOMERGE.
>>
>> Signed-off-by: Ming Lei <ming.lei@canonical.com>
>> ---
>>  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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[PATCH 0/4] block: some misc changes Ming Lei <ming.lei@canonical.com> - 2015-10-14 05:40 +0200
  [PATCH 1/4] block: setup bi_phys_segments after splitting Ming Lei <ming.lei@canonical.com> - 2015-10-14 05:40 +0200
    Re: [PATCH 1/4] block: setup bi_phys_segments after splitting Jeff Moyer <jmoyer@redhat.com> - 2015-10-15 17:20 +0200
  [PATCH 3/4] blk-mq: check bio_mergeable() early before merging Ming Lei <ming.lei@canonical.com> - 2015-10-14 05:40 +0200
    Re: [PATCH 3/4] blk-mq: check bio_mergeable() early before merging Jeff Moyer <jmoyer@redhat.com> - 2015-10-15 17:30 +0200
      Re: [PATCH 3/4] blk-mq: check bio_mergeable() early before merging Ming Lei <ming.lei@canonical.com> - 2015-10-16 02:30 +0200
  [PATCH 4/4] blk-mq: mark ctx as pending at batch in flush plug path Ming Lei <ming.lei@canonical.com> - 2015-10-14 05:40 +0200
    Re: [PATCH 4/4] blk-mq: mark ctx as pending at batch in flush plug path Jeff Moyer <jmoyer@redhat.com> - 2015-10-15 17:30 +0200
      Re: [PATCH 4/4] blk-mq: mark ctx as pending at batch in flush plug path Ming Lei <ming.lei@canonical.com> - 2015-10-16 02:30 +0200
  [PATCH 2/4] block: avoid to merge splitted bio Ming Lei <ming.lei@canonical.com> - 2015-10-14 05:40 +0200
    Re: [PATCH 2/4] block: avoid to merge splitted bio Jeff Moyer <jmoyer@redhat.com> - 2015-10-15 17:20 +0200

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