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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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