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

[Paul Menzel]

Dear Yu,


Am 15.09.22 um 09:21 schrieb Yu Kuai:

> 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?

Yes, sure.


Kind regards,

Paul