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

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Message-ID: <CALvZod7X6FOMnZT48Q9Joh_nha6NMXntL3XqMDqRYFZ1ULgh=w@mail.gmail.com>
Date:   Wed, 2 Jan 2019 13:45:49 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Yang Shi <yang.shi@...ux.alibaba.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 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.

> 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