Re: [PATCH v8 2/6] memcontrol: implement mem_cgroup_tryget_online()

[Yosry Ahmed <yosryahmed@google.com>]

On Thu, Nov 30, 2023 at 11:40 AM Nhat Pham <nphamcs@gmail.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@gmail.com>

Reviewed-by: Yosry Ahmed <yosryahmed@google.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