linux-kernel - Re: [PATCH v8 2/6] memcontrol: implement mem_cgroup_tryget

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Date:   Tue, 5 Dec 2023 11:55:39 -0800
From:   Nhat Pham <nphamcs@...il.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org,
        cerasuolodomenico@...il.com, sjenning@...hat.com,
        ddstreet@...e.org, vitaly.wool@...sulko.com, mhocko@...nel.org,
        roman.gushchin@...ux.dev, shakeelb@...gle.com,
        muchun.song@...ux.dev, chrisl@...nel.org, linux-mm@...ck.org,
        kernel-team@...a.com, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org, shuah@...nel.org
Subject: Re: [PATCH v8 2/6] memcontrol: implement mem_cgroup_tryget_online()

On Tue, Dec 5, 2023 at 10:03 AM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> On Thu, Nov 30, 2023 at 11:40 AM Nhat Pham <nphamcs@...il.com> wrote:
> >
> > This patch implements a helper function that try to get a reference to
> > an memcg's css, as well as checking if it is online. This new function
> > is almost exactly the same as the existing mem_cgroup_tryget(), except
> > for the onlineness check. In the !CONFIG_MEMCG case, it always returns
> > true, analogous to mem_cgroup_tryget(). This is useful for e.g to the
> > new zswap writeback scheme, where we need to select the next online
> > memcg as a candidate for the global limit reclaim.
> >
> > Signed-off-by: Nhat Pham <nphamcs@...il.com>
>
> Reviewed-by: Yosry Ahmed <yosryahmed@...gle.com>

Thanks for the review, Yosry :) Really appreciate the effort and your
comments so far.

>
> > ---
> >  include/linux/memcontrol.h | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index 7bdcf3020d7a..2bd7d14ace78 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -821,6 +821,11 @@ static inline bool mem_cgroup_tryget(struct mem_cgroup *memcg)
> >         return !memcg || css_tryget(&memcg->css);
> >  }
> >
> > +static inline bool mem_cgroup_tryget_online(struct mem_cgroup *memcg)
> > +{
> > +       return !memcg || css_tryget_online(&memcg->css);
> > +}
> > +
> >  static inline void mem_cgroup_put(struct mem_cgroup *memcg)
> >  {
> >         if (memcg)
> > @@ -1349,6 +1354,11 @@ static inline bool mem_cgroup_tryget(struct mem_cgroup *memcg)
> >         return true;
> >  }
> >
> > +static inline bool mem_cgroup_tryget_online(struct mem_cgroup *memcg)
> > +{
> > +       return true;
> > +}
> > +
> >  static inline void mem_cgroup_put(struct mem_cgroup *memcg)
> >  {
> >  }
> > --
> > 2.34.1