On Tue, Apr 14, 2020 at 3:31 AM Chris Down chris@chrisdown.name wrote:
Hi Yafang,
Yafang Shao writes:
A recent commit 9852ae3fe529 ("mm, memcg: consider subtrees in memory.events") changes the behavior of memcg events, which will consider subtrees in memory.events. But oom_kill event is a special one as it is used in both cgroup1 and cgroup2. In cgroup1, it is displayed in memory.oom_control. The file memory.oom_control is in both root memcg and non root memcg, that is different with memory.event as it only in non-root memcg. That commit is okay for cgroup2, but it is not okay for cgroup1 as it will cause inconsistent behavior between root memcg and non-root memcg. Let's recover the original behavior for cgroup1.
Can you please explain the practical ramifications of this and show an explicitly laid out example of how this manifests, with numbers and scenarios? It's unclear to me that this is a real problem as is -- it may be, but there certainly needs to be more information.
Here's an example.
root memcg / memcg foo / memcg bar
Suppose there's an oom_kill in memcg bar, then the oon_kill will be
root memcg : memory.oom_control(oom_kill) 0 / memcg foo : memory.oom_control(oom_kill) 1 / memcg bar : memory.oom_control(oom_kill) 1
Then the user has to know whether the memcg is root or not, if it is root memcg, then memory.oom_control(oom_kill) is its local event only, while if it is not root memcg, then memory.oom_control(oom_kill) includes all its descendants' oom_kill events.
Thanks Yafang