Re: [PATCH V4 1/4] block: avoid double io accounting for flush request

Bart Van Assche
2021-04-30T02:51:42Z

On 4/28/21 7:34 PM, Ming Lei wrote:
> For flush request, rq->end_io() may be called two times, one is from
> timeout handling(blk_mq_check_expired()), another is from normal
> completion(__blk_mq_end_request()).
>
> Move blk_account_io_flush() after flush_rq->ref drops to zero, so
> io accounting can be done just once for flush request.
>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> block/blk-flush.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/block/blk-flush.c b/block/blk-flush.c
> index 7942ca6ed321..1002f6c58181 100644
> --- a/block/blk-flush.c
> +++ b/block/blk-flush.c
> @@ -219,8 +219,6 @@ static void flush_end_io(struct request *flush_rq, blk_status_t error)
> unsigned long flags = 0;
> struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
>
> - blk_account_io_flush(flush_rq);
> -
> /* release the tag's ownership to the req cloned from */
> spin_lock_irqsave(&fq->mq_flush_lock, flags);
>
> @@ -230,6 +228,7 @@ static void flush_end_io(struct request *flush_rq, blk_status_t error)
> return;
> }
>
> + blk_account_io_flush(flush_rq);
> /*
> * Flush request has to be marked as IDLE when it is really ended
> * because its .end_io() is called from timeout code path too for

How about adding the following:

Fixes: b68663186577 ("block: add iostat counters for flush requests")

Anyway:

Reviewed-by: Bart Van Assche <bvanassche@acm.org>