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Date:   Thu, 10 Jun 2021 12:00:28 +0200
From:   Michal Hocko <mhocko@suse.com>
To:     Aaron Tomlin <atomlin@redhat.com>
Cc:     Waiman Long <llong@redhat.com>, Shakeel Butt <shakeelb@google.com>,
        Linux MM <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] mm/oom_kill: allow oom kill allocating task for
 non-global case
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On Wed 09-06-21 15:35:34, Aaron Tomlin wrote:
> On Tue 2021-06-08 08:22 +0200, Michal Hocko wrote:
> > Is it possible the only eligible task has been killed and oom reaped
> > already?
> 
> Yes, I suspect so; and I had a look at the vmcore, the task in the OOM
> report is no longer present. Therefore, I suspect the task namely "node"
> (i.e. PID 1703345) was OOM killed i.e. a SIGKILL was sent and was granted
> access to memory reserves and selected/or choosen by the OOM reaper for
> termination; the victim then raised a page fault that triggered yet
> another "charge" in the memcg that exceeded the memory limit set on the
> container;

If that was the case then the allocating (charging) task would not hit
the oom path at all
stable/linux-4.18.y:mm/memcontrol.c
try_charge()
        /*
         * Unlike in global OOM situations, memcg is not in a physical
         * memory shortage.  Allow dying and OOM-killed tasks to
         * bypass the last charges so that they can exit quickly and
         * free their memory.
         */
        if (unlikely(tsk_is_oom_victim(current) ||
                     fatal_signal_pending(current) ||
                     current->flags & PF_EXITING))
                goto force;

If you have a crash dump available then you can check the memcg
associate with the allocating task and check whether it is really marked
as OOM victim.

> and since no other task in the memcg had a suitable OOM score
> and the allocating task/or victim was "unkillable" i.e. already selected
> for termination by the OOM reaper, we got the message: "Out of memory and
> no killable processes...".

What do you mean by allocating task being unkillable?

-- 
Michal Hocko
SUSE Labs