On Mon, Apr 13, 2020 at 5:36 PM Yafang Shao laoar.shao@gmail.com wrote:
On Tue, Apr 14, 2020 at 1:06 AM Shakeel Butt shakeelb@google.com wrote:
On Sun, Apr 12, 2020 at 7:04 AM Yafang Shao laoar.shao@gmail.com wrote:
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.
I still couldn't understand the cgroup v1's root vs non_root behavior change. The behavior change I see is the hierarchical one i.e. MEMCG_OOM_KILL event in the descendant will cause the notification and count increment in the ancestors even in the cgroup v1.
For the non-root memcg, its memory.oom_control(oom_kill) includes its descendants' oom_kill, but for root memcg, it doesn't include its descendants' oom_kill. That means, memory.oom_control(oom_kill) has different meanings in different memcgs. That is inconsistent.
[snip]
I suppose we don't want that behavior change in v1.
That is another topic. I think this feature is welcomed to cgroup1, if we can fully support it, for example by adding memory.events.local into cgroup1 as well, but as far as I know the cgroup1 is frozen.
Please note that after your patch the non-root memcg's memory.oom_control(oom_kill) will not include the descendant's oom_kill anymore. The non-root and root memcg's memory.oom_control(oom_kill) will not be hierarchical anymore but consistent. I think that was the intention of the patch, right?
Let's recover the original behavior for cgroup1.
Fixes: 9852ae3fe529 ("mm, memcg: consider subtrees in memory.events") Cc: Chris Down chris@chrisdown.name Cc: Johannes Weiner hannes@cmpxchg.org Cc: Shakeel Butt shakeelb@google.com Cc: stable@vger.kernel.org Signed-off-by: Yafang Shao laoar.shao@gmail.com
include/linux/memcontrol.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 8c340e6b347f..a0ae080a67d1 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -798,7 +798,8 @@ static inline void memcg_memory_event(struct mem_cgroup *memcg, atomic_long_inc(&memcg->memory_events[event]); cgroup_file_notify(&memcg->events_file);
if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS ||!cgroup_subsys_on_dfl(memory_cgrp_subsys)) break; } while ((memcg = parent_mem_cgroup(memcg)) && !mem_cgroup_is_root(memcg));-- 2.18.2
Thanks Yafang