kselftests: memcg: update the oom group leaf events test

kselftests: memcg: update the oom group leaf events test

Patch series "mm: memcg kselftests fixes".

This patch (of 4):

Commit 9852ae3fe529 ("mm, memcg: consider subtrees in memory.events") made
memory.events recursive: all events are propagated upwards by the tree.
It was a change in semantics.

It broke the oom group leaf events test: it assumes that after an OOM the
oom_kill counter is zero on parent's level.

Let's adjust the test: it should have similar expectations for the child
and parent levels.

The test passes after this fix.

Link: https://lkml.kernel.org/r/20220415000133.3955987-2-roman.gushchin@linux.dev
Link: https://lkml.kernel.org/r/20220415000133.3955987-1-roman.gushchin@linux.dev
Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Reviewed-by: David Vernet <void@manifault.com>
Cc: Chris Down <chris@chrisdown.name>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>