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

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Message-ID: <CAF8kJuOsaX15w3gF7eUN8u7LAKhC7m2we91simoPH7S=MZJZCg@mail.gmail.com>
Date:   Mon, 4 Dec 2023 16:35:57 -0800
From:   Chris Li <chrisl@...nel.org>
To:     Nhat Pham <nphamcs@...il.com>
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()

Hi Nhat,

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.

Chris

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.

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.

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
>