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From:   Ming Lei <tom.leiming@gmail.com>
Date:   Thu, 4 Apr 2019 14:53:37 +0800
Message-ID: <CACVXFVOm17EvGVD7AiEWY8VUbPqCo2benoOLx-1hWyM99++0sA@mail.gmail.com>
Subject: Re: [PATCH 1/1] blk-mq: do not reset plug->rq_count before the list
 is sorted
To:     Dongli Zhang <dongli.zhang@oracle.com>
Cc:     Jens Axboe <axboe@kernel.dk>,
        linux-block <linux-block@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, Apr 4, 2019 at 10:54 AM Dongli Zhang <dongli.zhang@oracle.com> wrote:
>
> We would never be able to sort the list if we first reset plug->rq_count
> which is used in conditional check later.
>
> Fixes: ce5b009cff19 ("block: improve logic around when to sort a plug list")
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> ---
>  block/blk-mq.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 3ff3d7b..c162718 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1711,11 +1711,12 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
>         unsigned int depth;
>
>         list_splice_init(&plug->mq_list, &list);
> -       plug->rq_count = 0;
>
>         if (plug->rq_count > 2 && plug->multiple_queues)
>                 list_sort(NULL, &list, plug_rq_cmp);
>
> +       plug->rq_count = 0;
> +
>         this_q = NULL;
>         this_hctx = NULL;
>         this_ctx = NULL;
> --
> 2.7.4
>

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming Lei