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: <20120912170933.GO7677@google.com>
Date:	Wed, 12 Sep 2012 10:09:33 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, 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>,
	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>
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 Wed, Sep 12, 2012 at 01:56:09PM +0400, Glauber Costa wrote:
> "Being able to provide hierarchical support" is an example of such
> restrictions. And as Vivek said himself, for the CFQ case should be doable.

Yeah, it's mostly that cfq was already a hairy monster before blkcg
was added to it and unfortunately we didn't make it any cleaner in the
process and blkcg itself has a lot of other issues including being
completely broken w.r.t. writeback writes.  In addition there are two
sub-controllers - the cfq one and blk-throttle.  So, it's just that
there are too many scary things to do and not enough man power or
maybe interest.  I hope we could just declare cgroup isn't supported
on block devices but that doesn't seem feasible at this point either.

I might / probably work on it and am hoping to coerce Vivek into it
too.  If you wanna jump in, please be my guest.

Thanks.

-- 
tejun
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