[Devel] Re: [PATCH v5 06/14] memcg: kmem controller infrastructure

[Glauber Costa]

On 10/20/2012 12:34 AM, David Rientjes wrote:
> On Fri, 19 Oct 2012, Glauber Costa wrote:
> 
>>>>> What about gfp & __GFP_FS?
>>>>>
>>>>
>>>> Do you intend to prevent or allow OOM under that flag? I personally
>>>> think that anything that accepts to be OOM-killed should have GFP_WAIT
>>>> set, so that ought to be enough.
>>>>
>>>
>>> The oom killer in the page allocator cannot trigger without __GFP_FS 
>>> because direct reclaim has little chance of being very successful and 
>>> thus we end up needlessly killing processes, and that tends to happen 
>>> quite a bit if we dont check for it.  Seems like this would also happen 
>>> with memcg if mem_cgroup_reclaim() has a large probability of failing?
>>>
>>
>> I can indeed see tests for GFP_FS in some key locations in mm/ before
>> calling the OOM Killer.
>>
>> Should I test for GFP_IO as well?
> 
> It's not really necessary, if __GFP_IO isn't set then it wouldn't make 
> sense for __GFP_FS to be set.
> 
>> If the idea is preventing OOM to
>> trigger for allocations that can write their pages back, how would you
>> feel about the following test:
>>
>> may_oom = (gfp & GFP_KERNEL) && !(gfp & __GFP_NORETRY) ?
>>
> 
> I would simply copy the logic from the page allocator and only trigger oom 
> for __GFP_FS and !__GFP_NORETRY.
> 

That seems reasonable to me. Michal ?