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Date:   Fri, 16 Dec 2022 15:50:49 +0800
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Subject: Re: [PATCH] mm/memcontrol: Skip root memcg in memcg_memory_event_mm
To:     Shakeel Butt <shakeelb@google.com>
Cc:     akpm@linux-foundation.org, roman.gushchin@linux.dev,
        songmuchun@bytedance.com, hannes@cmpxchg.org, vbabka@suse.cz,
        willy@infradead.org, vasily.averin@linux.dev,
        linux-kernel@vger.kernel.org
References: <20221215091907.763801-1-haifeng.xu@shopee.com>
 <20221215181803.ome46pkh6g7qu3t4@google.com>
 <abec13da-c74a-0fd8-74e0-3cdc547e4e08@shopee.com>
 <20221216064210.krxtxebuwc7dijzu@google.com>
 <13c73151-4b28-4324-afd5-8b84b82bc25d@shopee.com>
 <20221216073640.xjtpsyigoej77v5h@google.com>
From:   Haifeng Xu <haifeng.xu@shopee.com>
In-Reply-To: <20221216073640.xjtpsyigoej77v5h@google.com>
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On 2022/12/16 15:36, Shakeel Butt wrote:
> On Fri, Dec 16, 2022 at 03:28:53PM +0800, Haifeng Xu wrote:
>>
>>
>> On 2022/12/16 14:42, Shakeel Butt wrote:
>>> On Fri, Dec 16, 2022 at 09:43:02AM +0800, Haifeng Xu wrote:
>>>>
>>>>
>>>> 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.
>>>>
>>>
>>> What about v1's memory.oom_control?
>>>
>>  
>> The memory.oom_control doesn't set the CFTYPE_NOT_ON_ROOT flag. But oom_kill_disable or
>> under_oom actually only support non-root memcg, so the memory_events should be consistent
>> with them.
> 
> Did you take a look at mem_cgroup_oom_control_read()? It is displaying
> MEMCG_OOM_KILL for root memcg. Irrespective it makes sense or not, you
> want to change behavior of user visible interface. If you really want to
> then propose for the deprecation of that interface.

Yes, I have see it in mem_cgroup_oom_control_read() and I think that 
showing MEMCG_OOM_KILL for root memcg doesn't make much sense.

Shoud I add the CFTYPE_NOT_ON_ROOT flag for cgroup v1?