Re: [External] Re: [PATCH] memcg: Don't wait writeback completion when release memcg.

[Julian Sun <sunjunchao@bytedance.com>]

On Thu, Aug 21, 2025 at 4:58 AM Tejun Heo <tj@kernel.org> wrote:
>
> On Wed, Aug 20, 2025 at 07:19:40PM +0800, Julian Sun wrote:
> > @@ -3912,8 +3921,12 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
> >       int __maybe_unused i;
> >
> >  #ifdef CONFIG_CGROUP_WRITEBACK
> > -     for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++)
> > -             wb_wait_for_completion(&memcg->cgwb_frn[i].done);
> > +     for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++) {
> > +             struct wb_completion *done = memcg->cgwb_frn[i].done;
> > +
> > +             if (atomic_dec_and_test(&done->cnt))
> > +                     kfree(done);
> > +     }
> >  #endif
>
> Can't you just remove done? I don't think it's doing anything after your
> changes anyway.

Thanks for your review.

AFAICT done is also used to track free slots in
mem_cgroup_track_foreign_dirty_slowpath() and
mem_cgroup_flush_foreign(), otherwise we have no method to know which
one is free and might flush more than what MEMCG_CGWB_FRN_CNT allow.

Am I missing something?

Thanks,
>
> Thanks.
>
> --
> tejun