Re: [PATCH] mm: add group_oom_kill memory event

[Chris Down]

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@xxxxxxxxx>

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

Acked-by: Chris Down <chris@xxxxxxxxxxxxxx>

> ---
> 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"?