Re: [PATCH] mm: fix oom work when memory is under pressure

[zhong jiang <zhongjiang@huawei.com>]

On 2016/9/13 1:44, Michal Hocko wrote:
> On Mon 12-09-16 21:42:28, zhong jiang wrote:
>> On 2016/9/12 19:13, Michal Hocko wrote:
>>> On Mon 12-09-16 17:51:06, zhong jiang wrote:
>>> [...]
>>>> hi,  Michal
>>>> oom reaper indeed can accelerate the recovery of memory, but the patch
>>>> solve the extreme scenario, I hit it by runing trinity. I think the
>>>> scenario can happen whether oom reaper or not.
>>> could you be more specific about the case when the oom reaper and the
>>> current oom code led to the oom deadlock?
>> It is not the oom deadlock.  It will lead to hungtask.  The explain is
>> as follows.
>>
>> process A occupy a resource and lock it. then A need to allocate
>> memory when memory is very low. at the some time, oom will come up and
>> return directly. because it find other process is freeing memory in
>> same zone.
>>
>> however, the freed memory is taken away by another process.
>> it will lead to A oom again and again.
>>
>> process B still wait some resource holded by A. so B will obtain the
>> lock until A release the resource. therefor, if A spend much time to
>> obtain memory, B will hungtask.
> OK, I see what you are aiming for. And indeed such a starvation and
> resulting priority inversion is possible. It is a hard problem to solve
> and your patch doesn't address it either. You can spend enough time
> reclaiming and retrying without ever getting to the oom path to trigger
> this hungtask warning.
  Yes.
> If you want to solve this problem properly then you would have to give
> tasks which are looping in the page allocator access to some portion of
> memory reserves. This is quite tricky to do right, though.
  To use some portion of memory reserves is almost no effect in a so starvation scenario.
   I think the hungtask still will occur. it can not  solve the problem primarily.
> Retry counters with the fail path have been proposed in the past and not
> accepted.
  The above patch have been tested by runing the trinity.  The question is fixed. 
  Is there  any reasonable reason oppose to the patch ?  or it will bring in  any side-effect.

 Thanks
zhongjiang


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