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

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Date:   Wed, 4 Oct 2017 15:27:20 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Roman Gushchin <guro@...com>
Cc:     linux-mm@...ck.org, Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, kernel-team@...com,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v10 3/6] mm, oom: cgroup-aware OOM killer

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@...com>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Vladimir Davydov <vdavydov.dev@...il.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: kernel-team@...com
> Cc: cgroups@...r.kernel.org
> Cc: linux-doc@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-mm@...ck.org

This looks good to me.

Acked-by: Johannes Weiner <hannes@...xchg.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.