Re: new cg-manager gui tool for managin cgroups

[Lennart Poettering <mzerqung@0pointer.de>]

On Wed, 20.07.11 16:42, Vivek Goyal (vgoyal@redhat.com) wrote:

> 
> On Wed, Jul 20, 2011 at 10:28:32PM +0200, Lennart Poettering wrote:
> 
> [..]
> > 
> > > Right now, the gui assumes that the various hierarchies are mounted separately,
> > > but that the cpu and cpuacct are co-mounted. Its my understanding that this
> > > is consistent with how systemd is doing things. So that's great.
> > 
> > In F15 we mount all controllers enabled in the kernel separately. In F16
> > we'll optionally mount some of them together, and we'll probably ship a
> > default of mounting cpu and cpuacct together if they are both enabled.
> 
> Last time we talked about possibility of co-mounting memory and IO at some
> point of time and you said it is a bad idea from applications programming
> point of view.  Has that changed now?

Well, no, but yes.

After discussing this Dhaval the scheme we came up with is to add
symlinks to /sys/fs/cgroup/ so that even when some controllers are
mounted together they are still available at the the separate
directories. Example, if we mount cpu+cpuacct together things will look
like this:

/sys/fs/cgroup/cpu+cpuacct is the joint mount point.

/sys/fs/cgroup/cpu → /sys/fs/cgroup/cpu+cpuacct is a symlink.

/sys/fs/cgroup/cpuacct → /sys/fs/cgroup/cpu+cpuacct is a symlink.

That way to most applications it will be very easy to support this: they
can simply assume that the controller "foobar" is available under
/sys/fs/cgroup/foobar, and that's it.

Lennart

-- 
Lennart Poettering - Red Hat, Inc.
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