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Date: Fri, 14 Sep 2012 11:53:24 -0700
From: Tejun Heo <tj@kernel.org>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: containers@lists.linux-foundation.org, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, Li Zefan <lizefan@huawei.com>,
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        Johannes Weiner <hannes@cmpxchg.org>, Thomas Graf <tgraf@suug.ch>,
        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>,
        Serge Hallyn <serge.hallyn@ubuntu.com>
Subject: Re: [RFC] cgroup TODOs
Message-ID: <20120914185324.GI17747@google.com>
References: <20120913205827.GO7677@google.com>
 <20120914180754.GF6221@redhat.com>
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Hello, Vivek.

On Fri, Sep 14, 2012 at 02:07:54PM -0400, Vivek Goyal wrote:
> I am curious that why are you planning to provide capability of controller
> specific view of hierarchy. To me it sounds pretty close to having
> separate hierarchies per controller. Just that it is a little more
> restricted configuration. 

I think it's a lot less crazy and gives us a way to bind a resource to
a set of controller cgroups regardless which task is looking at it,
which is something we're sorely missing now.

> IOW, who is is the user of this functionality and who is asking for it.
> Can we go all out where all controllers have only one hierarchy view.

I think the issue is that controllers inherently have overhead and
behavior alterations depending on the tree organization.  At least
from the usage I see from google which uses nested cgroups
extensively, at least that level of flexibility seems necessary.

In addition, for some resources, granularity beyond certain point
simply doesn't work.  Per-service granularity might make sense for cpu
but applying it by default would be silly for blkio.

Thanks.

-- 
tejun