linux-kernel - Re: [RFC PATCH] mm: memcontrol: memory+swap accounting for cgroup-v2

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Message-ID: <20171219173354.GQ3919388@devbig577.frc2.facebook.com>
Date:   Tue, 19 Dec 2017 09:33:54 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Michal Hocko <mhocko@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Roman Gushchin <guro@...com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Greg Thelen <gthelen@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Cgroups <cgroups@...r.kernel.org>, linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH] mm: memcontrol: memory+swap accounting for cgroup-v2

Hello,

On Tue, Dec 19, 2017 at 09:23:29AM -0800, Shakeel Butt wrote:
> To provide consistent memory usage history using the current
> cgroup-v2's 'swap' interface, an additional metric expressing the
> intersection of memory and swap has to be exposed. Basically memsw is
> the union of memory and swap. So, if that additional metric can be

Exposing anonymous pages with swap backing sounds pretty trivial.

> used to find the union. However for consistent memory limit
> enforcement, I don't think there is an easy way to use current 'swap'
> interface.

Can you please go into details on why this is important?  I get that
you can't do it as easily w/o memsw but I don't understand why this is
a critical feature.  Why is that?

Thanks.

-- 
tejun