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SubjectRe: [PATCH] cgroupfs: create /sys/fs/cgroup to mount cgroupfs on
* Vivek Goyal <vgoyal@redhat.com> [2010-07-22 17:26:34]:

> On Thu, Jul 22, 2010 at 02:18:56PM -0700, Greg KH wrote:
> > On Thu, Jul 22, 2010 at 03:37:41PM -0400, Vivek Goyal wrote:
> > > On Thu, Jul 22, 2010 at 11:36:15AM -0700, Greg KH wrote:
> > > > On Thu, Jul 22, 2010 at 11:31:07AM -0700, Paul Menage wrote:
> > > > > On Thu, Jul 22, 2010 at 11:26 AM, Greg KH <gregkh@suse.de> wrote:
> > > > > > We really shouldn't be asking userspace to create new root filesystems.
> > > > > > So follow along with all of the other in-kernel filesystems, and provide
> > > > > > a mount point in sysfs.
> > > > > >
> > > > > > For cgroupfs, this should be in /sys/fs/cgroup/  This change provides
> > > > > > that mount point when the cgroup filesystem is registered in the kernel.
> > > > >
> > > > > But cgroups will typically have multiple mounts, with different
> > > > > resource controllers/options on each mount. That doesn't really fit in
> > > > > with this scheme.
> > > >
> > > > Really? I see systems mounting it at /cgroups/ in the filesystem today.
> > > > Where are you expecting it to be mounted at?
> > > >
> > >
> > > Greg,
> > >
> > > [CCing few more folks who might be interested in this dicussion ]
> > >
> > > We do want to retain facility to mount different controllers at different
> > > mount points. We were discussing the other day that in libvirt we might
> > > want to mount block IO controller and network controller separately as
> > > by default we will not put a new virtual machine in a cgroup of its own
> > > because of the penatly involved.
> >
> > That's fine, I'm not changing that ability at all. We just need a
> > "default" mount point for "normal" users.
> >
> > > For other controllers like cpu, memory etc, libvirt automatically puts
> > > each new virtual machine in a cgroup of own. So this is one use case
> > > where we might want to mount different controllers at different mount
> > > points.
> > >
> > > For my testing I now always use /cgroup/ and create directories under it
> > > /cgroup/blkio /cgroup/cpu etc and mount controllers on respective
> > > directories.
> >
> > Lennart and Kay, is this what systemd is doing? I really don't think we
> > should be adding a root /cgroup/ mount point to the system for something
> > like this.
> >
> > Maybe /dev/cgroup/ is better to use, as that way users can create
> > sub-mount points easier. They can't do that in /sys/fs/cgroup/
>
> The only problem with /dev/cgroup seems to be that it seems little
> unintutive. To me, we have devices under /dev/ dir and cgroups are not
> devices.
>
> I think people have floated similar threads in the past on lkml with
> various opinions and everybody had their own choices but nothing was
> conclusive.
>
> Polluting / definitely sounds odd but it does not look that bad once
> we can't find any other good choices.
>

I think it breaks the filesystem hierarchy standard and I've seen
bugzilla's around it. I'd prefer /sys/fs/cgroup.

--
Three Cheers,
Balbir
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