linux-kernel - Re: [PATCH] mm: add group_oom

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Date:   Sat, 4 Dec 2021 09:36:46 +0000
From:   Chris Down <chris@...isdown.name>
To:     Dan Schatzberg <schatzberg.dan@...il.com>
Cc:     Johannes Weiner <hannes@...xchg.org>, Roman Gushchin <guro@...com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Jonathan Corbet <corbet@....net>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Muchun Song <songmuchun@...edance.com>,
        Alex Shi <alexs@...nel.org>,
        Wei Yang <richard.weiyang@...il.com>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" 
        <linux-mm@...ck.org>
Subject: Re: [PATCH] mm: add group_oom_kill memory event

Dan Schatzberg writes:
>Our container agent wants to know when a container exits if it was OOM
>killed or not to report to the user. We use memory.oom.group = 1 to
>ensure that OOM kills within the container's cgroup kill
>everything. Existing memory.events are insufficient for knowing if
>this triggered:
>
>1) Our current approach reads memory.events oom_kill and reports the
>container was killed if the value is non-zero. This is erroneous in
>some cases where containers create their children cgroups with
>memory.oom.group=1 as such OOM kills will get counted against the
>container cgroup's oom_kill counter despite not actually OOM killing
>the entire container.
>
>2) Reading memory.events.local will fail to identify OOM kills in leaf
>cgroups (that don't set memory.oom.group) within the container cgroup.
>
>This patch adds a new oom_group_kill event when memory.oom.group
>triggers to allow userspace to cleanly identify when an entire cgroup
>is oom killed.
>
>Signed-off-by: Dan Schatzberg <schatzberg.dan@...il.com>

Thanks! Acking with one minor point on the documentation front.

Acked-by: Chris Down <chris@...isdown.name>

>---
> Documentation/admin-guide/cgroup-v2.rst | 4 ++++
> include/linux/memcontrol.h              | 1 +
> mm/memcontrol.c                         | 5 +++++
> mm/oom_kill.c                           | 1 +
> 4 files changed, 11 insertions(+)
>
>diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
>index 2aeb7ae8b393..eec830ce2068 100644
>--- a/Documentation/admin-guide/cgroup-v2.rst
>+++ b/Documentation/admin-guide/cgroup-v2.rst
>@@ -1268,6 +1268,10 @@ PAGE_SIZE multiple when read back.
> 		The number of processes belonging to this cgroup
> 		killed by any kind of OOM killer.
>
>+          oom_group_kill
>+                The number of times all tasks in the cgroup were killed
>+                due to memory.oom.group.

Maybe pedantic, but this reads as unclear to me whether in cgroup with 3 tasks 
we get the value "3" or "1" when a group kill occurs.

Maybe rephrase to not make be about tasks and just say "number of times a group 
OOM occurred"?