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    SubjectRe: [RFC] cgroup TODOs
    Hello, Vivek.

    On Fri, Sep 14, 2012 at 03:28:40PM -0400, Vivek Goyal wrote:
    > Hmm.., In that case how libvirt will make use of blkio in the proposed
    > scheme. We can't disable blkio nesting at "system" level. So We will
    > have to disable it at each service level except "libvirtd" so that
    > libvirt can use blkio for its virtual machines.
    >
    > That means blkio will see each service in a cgroup of its own and if
    > that does not make sense by default, its a problem. In the existing

    Yeap, if libvirtd wants use blkcg, blkcg will be enabled upto
    libvirtd's root. It might not be optimal but I think it makes sense.
    If you want to excercise hierarchical control on a resource, the only
    sane way is sticking to the hierarchy until it reaches root.

    > scheme, atleast every service does not show up in its cgroup from
    > blkio point of view. Everthig is in root and libvirt can create its
    > own cgroups, keeping number of cgroups small.

    Even a broken clock is right twice a day. I don't think this is a
    behavior we can keep for the sake of "but if we do this ass-weird
    thing, we can bypass the overhead for XYZ" when it breaks so many
    fundamental things.

    I think there currently is too much (broken) flexibility and intent to
    remove it. That doesn't mean that removeing all flexibility is the
    right direction. It inherently is a balancing act and I think the
    proposed solution is a reasonable tradeoff. There's important
    difference between causing full overhead by default for all users and
    requiring some overhead when the use case at hand calls for the
    functionality.

    Thanks.

    --
    tejun


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