linux-kernel - Re: [PATCH RFC cgroup/for-3.7] cgroup: mark subsystems with broken hierarchy support and whine if cgroups are nested for them

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Message-ID: <20120913174817.GA7677@google.com>
Date:	Thu, 13 Sep 2012 10:48:17 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.cz>,
	Li Zefan <lizf@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Turner <pjt@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Graf <tgraf@...g.ch>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Neil Horman <nhorman@...driver.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Dave Jones <davej@...hat.com>,
	Lennart Poettering <lennart@...ttering.net>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: [PATCH RFC cgroup/for-3.7] cgroup: mark subsystems with broken
 hierarchy support and whine if cgroups are nested for them

Hello, Glauber.

On Thu, Sep 13, 2012 at 03:53:56PM +0400, Glauber Costa wrote:
> Here is where the Kconfig option comes to play. If we do it in the
> kernel, userspace doesn't have to do anything. I spoke with Lennart and
> Kay, and at least from a systemd PoV, they would much rather not provide
> a hack in userspace for a file that is scheduled to go away in any case
> - which I personally believe is a fair request.
> 
> It is a default, so the effect for the user is the same: After the
> machine boots, use_hierarchy = 1, and he can still flip to 0 for some time.

Alright, let's go Kconfig.  Let's just make sure that the transitional
nature is clearly labeled and the fact that the default config will
generate a warning when nested cgroups are created in memcg.  We can
then coordinate the flip with distros.  Can you please repost the
Kconfig patch?

> > Setting mark on a parent should be reflected on all its children w/o
> > their own explicit settings.
> 
> That is clear, and better behavior than we have today. What I mean, is
> that by setting its own marking, the child can pretty much "escape" the
> group.
> 
> The ideal solution - from this point of view only - would be to have
> more than one marking, and mark with all the way down to the root. So if
> you have an iptables rule to match one marking, it still applies to the
> kids. And you can still have extra markings.
> 
> I am not sure this is feasible, though, in which case your solution
> could be a good compromise. But please let's aim for it.

I don't think it supports multiple tags.  If that's possible, it would
be nice but I don't think it's a must.

Thanks.

-- 
tejun
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