Re: [PATCH] mm/memcontrol: Skip root memcg in memcg_memory_event_mm

[Haifeng Xu]

On 2022/12/16 02:18, Shakeel Butt wrote:
> On Thu, Dec 15, 2022 at 09:19:07AM +0000, Haifeng Xu wrote:
>> The memory events aren't supported on root cgroup, so there is no need
>> to account MEMCG_OOM_KILL on root memcg.
>>
> 
> Can you explain the scenario where this is happening and causing issue
> for you?
> 
If the victim selected by oom killer belongs to root memcg, memcg_memory_event_mm
still counts the MEMCG_OOM_KILL event. This behavior is meaningless because the
flag of events/events.local in memory_files is CFTYPE_NOT_ON_ROOT. The root memcg
does not count any memory event.

>> Signed-off-by: Haifeng Xu <haifeng.xu@xxxxxxxxxx>
>> ---
>>  include/linux/memcontrol.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index 567f12323f55..09f75161a3bc 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -1142,7 +1142,7 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm,
>>  
>>  	rcu_read_lock();
>>  	memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
>> -	if (likely(memcg))
>> +	if (likely(memcg && !mem_cgroup_is_root(memcg)))
> 
> Even if we need this additional check, this is not the right place.
> 
>>  		memcg_memory_event(memcg, event);
>>  	rcu_read_unlock();
>>  }
>> -- 
>> 2.25.1
>>