linux-kernel - Re: [RFC PATCH] mm/oom_kill: allow oom kill allocating task for non-global case

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Date:   Mon, 7 Jun 2021 21:04:09 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Waiman Long <llong@...hat.com>
Cc:     Shakeel Butt <shakeelb@...gle.com>,
        Aaron Tomlin <atomlin@...hat.com>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] mm/oom_kill: allow oom kill allocating task for
 non-global case

On Mon 07-06-21 14:51:05, Waiman Long wrote:
> On 6/7/21 2:43 PM, Shakeel Butt wrote:
> > On Mon, Jun 7, 2021 at 9:45 AM Waiman Long <llong@...hat.com> wrote:
> > > On 6/7/21 12:31 PM, Aaron Tomlin wrote:
> > > > At the present time, in the context of memcg OOM, even when
> > > > sysctl_oom_kill_allocating_task is enabled/or set, the "allocating"
> > > > task cannot be selected, as a target for the OOM killer.
> > > > 
> > > > This patch removes the restriction entirely.
> > > > 
> > > > Signed-off-by: Aaron Tomlin <atomlin@...hat.com>
> > > > ---
> > > >    mm/oom_kill.c | 6 +++---
> > > >    1 file changed, 3 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > > > index eefd3f5fde46..3bae33e2d9c2 100644
> > > > --- a/mm/oom_kill.c
> > > > +++ b/mm/oom_kill.c
> > > > @@ -1089,9 +1089,9 @@ bool out_of_memory(struct oom_control *oc)
> > > >                oc->nodemask = NULL;
> > > >        check_panic_on_oom(oc);
> > > > 
> > > > -     if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
> > > > -         current->mm && !oom_unkillable_task(current) &&
> > > > -         oom_cpuset_eligible(current, oc) &&
> > > > +     if (sysctl_oom_kill_allocating_task && current->mm &&
> > > > +            !oom_unkillable_task(current) &&
> > > > +            oom_cpuset_eligible(current, oc) &&
> > > >            current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
> > > >                get_task_struct(current);
> > > >                oc->chosen = current;
> > > To provide more context for this patch, we are actually seeing that in a
> > > customer report about OOM happened in a container where the dominating
> > > task used up most of the memory and it happened to be the task that
> > > triggered the OOM with the result that no killable process could be
> > > found.
> > Why was there no killable process? What about the process allocating
> > the memory or is this remote memcg charging?
> 
> It is because the other processes have a oom_adjust_score of -1000. So they
> are non-killable. Anyway, they don't consume that much memory and killing
> them won't free up that much.
> 
> The other process that uses most of the memory is the one that trigger the
> OOM kill in the first place because the memory limit has been reached in new
> memory allocation. Based on the current logic, this process cannot be killed
> at all even if we set the oom_kill_allocating_task to 1 if the OOM happens
> only within the memcg context, not in a global OOM situation. This patch is
> to allow this process to be killed under this circumstance.

Do you have the oom report? I do not see why the allocating task hasn't
been chosen.
-- 
Michal Hocko
SUSE Labs