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

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Message-ID: <CAKEwX=NijPzqo3DXhfZ2HjYjOVHN=W__zQSJ24a-3P0egUYi3g@mail.gmail.com>
Date:   Tue, 5 Dec 2023 17:30:04 -0800
From:   Nhat Pham <nphamcs@...il.com>
To:     Chris Li <chrisl@...nel.org>
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org,
        cerasuolodomenico@...il.com, yosryahmed@...gle.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, 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 4:16 PM Chris Li <chrisl@...nel.org> wrote:
>
> On Mon, Dec 4, 2023 at 5:39 PM Nhat Pham <nphamcs@...il.com> wrote:
> >
> > > > memcg as a candidate for the global limit reclaim.
> > >
> > > Very minor nitpick. This patch can fold with the later patch that uses
> > > it. That makes the review easier, no need to cross reference different
> > > patches. It will also make it harder to introduce API that nobody
> > > uses.
> >
> > I don't have a strong preference one way or the other :) Probably not
> > worth the churn tho.
>
> Squashing a patch is very easy. If you are refreshing a new series, it
> is worthwhile to do it. I notice on the other thread Yosry pointed out
> you did  not use the function "mem_cgroup_tryget_online" in patch 3,
> that is exactly the situation my suggestion is trying to prevent.

I doubt squashing it would solve the issue - in fact, I think Yosry
noticed it precisely because he had to stare at a separate patch
detailing the adding of the new function in the first place :P

In general though, I'm hesitant to extend this API silently in a patch
that uses it. Is it not better to have a separate patch announcing
this API extension? list_lru_add() was originally part of the original
series too - we separate that out to its own thing because it gets
confusing. Another benefit is that there will be less work in the
future if we want to revert the per-cgroup zswap LRU patch, and
there's already another mem_cgroup_tryget_online() user - we can keep
this patch.

But yeah we'll see - I'll think about it if I actually have to send
v9. If not, let's not add unnecessary churning.

>
> If you don't have a strong preference, it sounds like you should squash it.
>
> Chris
>
> >
> > >
> > > Chris
> > >
> > > >
> > > > Signed-off-by: Nhat Pham <nphamcs@...il.com>
> > > > ---
> > > >  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
> > > >
> >