Re: [PATCH 2/3] mm: memcontrol: do not try to do swap when force empty

[Yang Shi <yang.shi@linux.alibaba.com>]

On 1/2/19 1:45 PM, Shakeel Butt wrote:
> On Wed, Jan 2, 2019 at 12:06 PM Yang Shi <yang.shi@linux.alibaba.com> wrote:
>> The typical usecase of force empty is to try to reclaim as much as
>> possible memory before offlining a memcg.  Since there should be no
>> attached tasks to offlining memcg, the tasks anonymous pages would have
>> already been freed or uncharged.
> Anon pages can come from tmpfs files as well.

Yes, but they are charged to swap space as regular anon pages.

>
>> Even though anonymous pages get
>> swapped out, but they still get charged to swap space.  So, it sounds
>> pointless to do swap for force empty.
>>
> I understand that force_empty is typically used before rmdir'ing a
> memcg but it might be used differently by some users. We use this
> interface to test memory reclaim behavior (anon and file).

Thanks for sharing your usecase. So, you uses this for test only?

>
> Anyways, I am not against changing the behavior, we can adapt
> internally but there might be other users using this interface
> differently.

Thanks.

Yang

>
> thanks,
> Shakeel