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Date: Wed, 12 Sep 2012 10:09:33 -0700
From: Tejun Heo <tj@kernel.org>
To: Glauber Costa <glommer@parallels.com>
Cc: Vivek Goyal <vgoyal@redhat.com>, linux-kernel@vger.kernel.org,
        Michal Hocko <mhocko@suse.cz>, Li Zefan <lizf@cn.fujitsu.com>,
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        "Serge E. Hallyn" <serue@us.ibm.com>,
        Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Neil Horman <nhorman@tuxdriver.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.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
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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