linux-kernel - Re: [PATCH] mm/oom_kill: count global and memory cgroup oom kills

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Date:   Tue, 23 May 2017 13:32:17 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Roman Guschin <guroan@...il.com>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>, hannes@...xchg.org
Subject: Re: [PATCH] mm/oom_kill: count global and memory cgroup oom kills



On 23.05.2017 10:49, David Rientjes wrote:
> On Mon, 22 May 2017, Konstantin Khlebnikov wrote:
> 
>> Nope, they are different. I think we should rephase documentation somehow
>>
>> low - count of reclaims below low level
>> high - count of post-allocation reclaims above high level
>> max - count of direct reclaims
>> oom - count of failed direct reclaims
>> oom_kill - count of oom killer invocations and killed processes
>>
> 
> In our kernel, we've maintained counts of oom kills per memcg for years as
> part of memory.oom_control for memcg v1, but we've also found it helpful
> to complement that with another count that specifies the number of
> processes oom killed that were attached to that exact memcg.
> 
> In your patch, oom_kill in memory.oom_control specifies that number of oom
> events that resulted in an oom kill of a process from that hierarchy, but
> not the number of processes killed from a specific memcg (the difference
> between oc->memcg and mem_cgroup_from_task(victim)).  Not sure if you
> would also find it helpful.
> 

This is worth addition. Let's call it "oom_victim" for short.

It allows to locate leaky part if they are spread over sub-containers within common limit.
But doesn't tell which limit caused this kill. For hierarchical limits this might be not so easy.

I think oom_kill better suits for automatic actions - restart affected hierarchy, increase limits, e.t.c.
But oom_victim allows to determine container affected by global oom killer.

So, probably it's worth to merge them together and increment oom_kill by global killer for victim memcg:

	if (!is_memcg_oom(oc)) {
		count_vm_event(OOM_KILL);
		mem_cgroup_count_vm_event(mm, OOM_KILL);
	} else
		mem_cgroup_event(oc->memcg, OOM_KILL);