Re: [v10 3/6] mm, oom: cgroup-aware OOM killer

Johannes Weiner
2017-10-04T19:27:36Z

On Wed, Oct 04, 2017 at 04:46:35PM +0100, Roman Gushchin wrote:
> Traditionally, the OOM killer is operating on a process level.
> Under oom conditions, it finds a process with the highest oom score
> and kills it.
>
> This behavior doesn't suit well the system with many running
> containers:
>
> 1) There is no fairness between containers. A small container with
> few large processes will be chosen over a large one with huge
> number of small processes.
>
> 2) Containers often do not expect that some random process inside
> will be killed. In many cases much safer behavior is to kill
> all tasks in the container. Traditionally, this was implemented
> in userspace, but doing it in the kernel has some advantages,
> especially in a case of a system-wide OOM.
>
> To address these issues, the cgroup-aware OOM killer is introduced.
>
> Under OOM conditions, it looks for the biggest leaf memory cgroup
> and kills the biggest task belonging to it. The following patches
> will extend this functionality to consider non-leaf memory cgroups
> as well, and also provide an ability to kill all tasks belonging
> to the victim cgroup.
>
> The root cgroup is treated as a leaf memory cgroup, so it's score
> is compared with leaf memory cgroups.
> Due to memcg statistics implementation a special algorithm
> is used for estimating it's oom_score: we define it as maximum
> oom_score of the belonging tasks.
>
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: kernel-team@fb.com
> Cc: cgroups@vger.kernel.org
> Cc: linux-doc@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-mm@kvack.org

This looks good to me.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

I just have one question:

> @@ -828,6 +828,12 @@ static void __oom_kill_process(struct task_struct *victim)
> struct mm_struct *mm;
> bool can_oom_reap = true;
>
> + if (is_global_init(victim) || (victim->flags & PF_KTHREAD) ||
> + victim->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
> + put_task_struct(victim);
> + return;
> + }
> +
> p = find_lock_task_mm(victim);
> if (!p) {
> put_task_struct(victim);

Is this necessary? The callers of this function use oom_badness() to
find a victim, and that filters init, kthread, OOM_SCORE_ADJ_MIN.