Re: [PATCH 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary

[Tetsuo Handa]

On 2020/08/20 23:00, Christian Brauner wrote:
> On Thu, Aug 20, 2020 at 10:48:43PM +0900, Tetsuo Handa wrote:
>> On 2020/08/20 22:34, Christian Brauner wrote:
>>> On Thu, Aug 20, 2020 at 03:26:31PM +0200, Michal Hocko wrote:
>>>> If you can handle vfork by other means then I am all for it. There were
>>>> no patches in that regard proposed yet. Maybe it will turn out simpler
>>>> then the heavy lifting we have to do in the oom specific code.
>>>
>>> Eric's not wrong. I fiddled with this too this morning but since
>>> oom_score_adj is fiddled with in a bunch of places this seemed way more
>>> code churn then what's proposed here.
>>
>> I prefer simply reverting commit 44a70adec910d692 ("mm, oom_adj: make sure
>> processes sharing mm have same view of oom_score_adj").
>>
>>   https://lore.kernel.org/patchwork/patch/1037208/
> 
> I guess this is a can of worms but just or the sake of getting more
> background: the question seems to be whether the oom adj score is a
> property of the task/thread-group or a property of the mm. I always
> thought the oom score is a property of the task/thread-group and not the
> mm which is also why it lives in struct signal_struct and not in struct
> mm_struct. But
> 
> 44a70adec910 ("mm, oom_adj: make sure processes sharing mm have same view of oom_score_adj")
> 
> reads like it is supposed to be a property of the mm or at least the
> change makes it so.

Yes, 44a70adec910 is trying to go towards changing from a property of the task/thread-group
to a property of mm. But I don't think we need to do it at the cost of "__set_oom_adj() latency
Yong-Taek Lee and Tim Murray have reported" and "complicity for supporting
vfork() => __set_oom_adj() => execve() sequence".