Re: [PATCH v2 1/4] md/raid10: cleanup wait_barrier()

[Yu Kuai]

Hi,

在 2022/09/15 0:16, Logan Gunthorpe 写道:
> On 2022-09-13 19:49, Yu Kuai wrote:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > Currently the nasty condition is wait_barrier() is hard to read. This
> > patch factor out the condition into a function.
> >
> > There are no functional changes.
> >
> > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> > ---
> >   drivers/md/raid10.c | 56 ++++++++++++++++++++++++++-------------------
> >   1 file changed, 32 insertions(+), 24 deletions(-)
> >
> > diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> > index 64d6e4cd8a3a..56458a53043d 100644
> > --- a/drivers/md/raid10.c
> > +++ b/drivers/md/raid10.c
> > @@ -957,44 +957,52 @@ static void lower_barrier(struct r10conf *conf)
> >   	wake_up(&conf->wait_barrier);
> >   }
> >   
> > +static bool stop_waiting_barrier(struct r10conf *conf)
> > +{
> > +	/* barrier is dropped */
> > +	if (!conf->barrier)
> > +		return true;
> > +
> > +	/*
> > +	 * If there are already pending requests (preventing the barrier from
> > +	 * rising completely), and the pre-process bio queue isn't empty, then
> > +	 * don't wait, as we need to empty that queue to get the nr_pending
> > +	 * count down.
> > +	 */
> > +	if (atomic_read(&conf->nr_pending)) {
> > +		struct bio_list *bio_list = current->bio_list;
>
> I'd probably just put the bio_list declaration at the top of this
> function, then the nested if statements are not necessary. The compiler
> should be able to optimize the access just fine.
>
> >   	if (conf->barrier) {
> > -		struct bio_list *bio_list = current->bio_list;
> > -		conf->nr_waiting++;
> > -		/* Wait for the barrier to drop.
> > -		 * However if there are already pending
> > -		 * requests (preventing the barrier from
> > -		 * rising completely), and the
> > -		 * pre-process bio queue isn't empty,
> > -		 * then don't wait, as we need to empty
> > -		 * that queue to get the nr_pending
> > -		 * count down.
> > -		 */
> >   		/* Return false when nowait flag is set */
> >   		if (nowait) {
> >   			ret = false;
> >   		} else {
> > +			conf->nr_waiting++;
>
> Technically speaking, I think moving nr_waiting counts as a functional
> change. As best as I can see it is correct, but it should probably be at
> least mentioned in the commit message, or maybe done as a separate
> commit with it's own justification. That way if it causes problems down
> the road, a bisect will make the issue clearer.

Thanks for your advice, I just think increase and decrease nr_waiting in
the case 'nowait' is pointless, and I move it incidentally.

I'll post a separate clean up patch to do that.

Paul, can I still add your Acked-by for this patch?

Thanks,
Kuai
> Thanks,
>
> Logan
> .