Re: [PATCH v4 2/4] mm/oom: handle remote ooms

[Shakeel Butt]

On Fri, Nov 19, 2021 at 8:50 PM Mina Almasry <almasrymina@xxxxxxxxxx> wrote:
>
[...]
> +/*
> + * Returns true if current's mm is a descendant of the memcg_under_oom (or
> + * equal to it). False otherwise. This is used by the oom-killer to detect
> + * ooms due to remote charging.
> + */
> +bool is_remote_oom(struct mem_cgroup *memcg_under_oom)
> +{
> +       struct mem_cgroup *current_memcg;
> +       bool is_remote_oom;
> +
> +       if (!memcg_under_oom)
> +               return false;
> +
> +       rcu_read_lock();
> +       current_memcg = mem_cgroup_from_task(current);
> +       if (current_memcg && !css_tryget_online(&current_memcg->css))

No need to grab a reference. You can call mem_cgroup_is_descendant() within rcu.

> +               current_memcg = NULL;
> +       rcu_read_unlock();
> +
> +       if (!current_memcg)
> +               return false;
> +
> +       is_remote_oom =
> +               !mem_cgroup_is_descendant(current_memcg, memcg_under_oom);
> +       css_put(&current_memcg->css);
> +
> +       return is_remote_oom;
> +}
> +