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

From: Yang Shi
Date: Thu Jan 03 2019 - 11:57:37 EST

On 1/2/19 1:45 PM, Shakeel Butt wrote:
On Wed, Jan 2, 2019 at 12:06 PM Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> 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