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

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Message-ID: <763b97f5-ea9c-e3e6-7fd9-0ab42cf09ca8@linux.alibaba.com>
Date:   Thu, 3 Jan 2019 08:56:30 -0800
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] mm: memcontrol: do not try to do swap when force
 empty



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