Re: [RFC] cgroup TODOs

From: Tejun Heo
Date: Fri Sep 14 2012 - 14:53:22 EST

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.


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