Re: [PATCH] mm: add group_oom_kill memory event

[Chris Down <chris@chrisdown.name>]

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@gmail.com>

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

Acked-by: Chris Down <chris@chrisdown.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"?