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From:   Shakeel Butt <shakeelb@google.com>
Date:   Wed, 2 Jan 2019 13:45:49 -0800
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Subject: Re: [PATCH 2/3] mm: memcontrol: do not try to do swap when force empty
To:     Yang Shi <yang.shi@linux.alibaba.com>
Cc:     Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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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.

> 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).

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

thanks,
Shakeel