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Date: Fri, 20 Dec 2013 12:00:59 -0500
From: Luiz Capitulino <lcapitulino@redhat.com>
To: Glauber Costa <glommer@gmail.com>
Cc: Vladimir Davydov <vdavydov@parallels.com>, dchinner@redhat.com,
        Michal Hocko <mhocko@suse.cz>, Johannes Weiner <hannes@cmpxchg.org>,
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        Glauber Costa <glommer@openvz.org>,
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        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [PATCH v14 16/18] vmpressure: in-kernel notifications
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On Fri, 20 Dec 2013 20:58:52 +0400
Glauber Costa <glommer@gmail.com> wrote:

> On Fri, Dec 20, 2013 at 8:53 PM, Luiz Capitulino <lcapitulino@redhat.com> wrote:
> > On Fri, 20 Dec 2013 20:46:05 +0400
> > Glauber Costa <glommer@gmail.com> wrote:
> >
> >> On Fri, Dec 20, 2013 at 8:44 PM, Luiz Capitulino <lcapitulino@redhat.com> wrote:
> >> > On Fri, 20 Dec 2013 10:03:32 -0500
> >> > Luiz Capitulino <lcapitulino@redhat.com> wrote:
> >> >
> >> >> > The answer for all of your questions above can be summarized by noting
> >> >> > that for the lack of other users (at the time), this patch does the bare minimum
> >> >> > for memcg needs. I agree, for instance, that it would be good to pass the level
> >> >> > but since memcg won't do anything with thta, I didn't pass it.
> >> >> >
> >> >> > That should be extended if you need to.
> >> >>
> >> >> That works for me. That is, including this minimal version first and
> >> >> extending it when we get in-tree users.
> >> >
> >> > Btw, there's something I was thinking just right now. If/when we
> >> > convert shrink functions to use this API, they will come to depend
> >> > on CONFIG_MEMCG=y. IOW, they won't work if CONFIG_MEMCG=n.
> >> >
> >> > Is this acceptable (this is an honest question)? Because today, they
> >> > do work when CONFIG_MEMCG=n. Should those shrink functions use the
> >> > shrinker API as a fallback?
> >>
> >> If you have a non-memcg user, that should obviously be available for
> >> CONFIG_MEMCG=n
> >
> > OK, which means we'll have to change it, right? Because, if I'm not
> > missing something, today vmpressure does depend on CONFIG_MEMCG=y.
> 
> You mean the main vmpressure mechanism?
> Sorry, this was out of my mental cachelines. Yes, vmpressure depends
> on MEMCG, because
> the pressure interface is memcg-specific (global == root memcg)
> 
> You might want to change that so you can reuse the mechanism and let
> only the user interface
> depend on memcg.

OK, that makes sense. Thanks Glauber.