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References: <20211120045011.3074840-1-almasrymina@google.com> <20211120045011.3074840-3-almasrymina@google.com>
In-Reply-To: <20211120045011.3074840-3-almasrymina@google.com>
From:   Shakeel Butt <shakeelb@google.com>
Date:   Fri, 19 Nov 2021 23:58:21 -0800
Message-ID: <CALvZod680y1o3WKFKEXmXf3Cd4j-POpc-zrAQ1+ykLoWK9-21A@mail.gmail.com>
Subject: Re: [PATCH v4 2/4] mm/oom: handle remote ooms
To:     Mina Almasry <almasrymina@google.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Hugh Dickins <hughd@google.com>, Shuah Khan <shuah@kernel.org>,
        Greg Thelen <gthelen@google.com>,
        Dave Chinner <david@fromorbit.com>,
        Matthew Wilcox <willy@infradead.org>,
        Roman Gushchin <guro@fb.com>, "Theodore Ts'o" <tytso@mit.edu>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, cgroups@vger.kernel.org
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Precedence: bulk

On Fri, Nov 19, 2021 at 8:50 PM Mina Almasry <almasrymina@google.com> 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;
> +}
> +