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    SubjectRe: The performance and behaviour of the anti-fragmentation related patches
    Linus Torvalds wrote:
    >
    > On Fri, 2 Mar 2007, Balbir Singh wrote:
    >>> My personal opinion is that while I'm not a huge fan of virtualization,
    >>> these kinds of things really _can_ be handled more cleanly at that layer,
    >>> and not in the kernel at all. Afaik, it's what IBM already does, and has
    >>> been doing for a while. There's no shame in looking at what already works,
    >>> especially if it's simpler.
    >> Could you please clarify as to what "that layer" means - is it the
    >> firmware/hardware for virtualization? or does it refer to user space?
    >
    > Virtualization in general. We don't know what it is - in IBM machines it's
    > a hypervisor. With Xen and VMware, it's usually a hypervisor too. With
    > KVM, it's obviously a host Linux kernel/user-process combination.
    >

    Thanks for clarifying.

    > The point being that in the guests, hotunplug is almost useless (for
    > bigger ranges), and we're much better off just telling the virtualization
    > hosts on a per-page level whether we care about a page or not, than to
    > worry about fragmentation.
    >
    > And in hosts, we usually don't care EITHER, since it's usually done in a
    > hypervisor.
    >
    >> It would also be useful to have a resource controller like per-container
    >> RSS control (container refers to a task grouping) within the kernel or
    >> non-virtualized environments as well.
    >
    > .. but this has again no impact on anti-fragmentation.
    >

    Yes, I agree that anti-fragmentation and resource management are independent
    of each other. I must admit to being a bit selfish here, in that my main
    interest is in resource management and we would love to see a well
    written and easy to understand resource management infrastructure and
    controllers to control CPU and memory usage. Since the issue of
    per-container RSS control came up, I wanted to ensure that we do not mix
    up resource control and anti-fragmentation.

    --
    Warm Regards,
    Balbir Singh
    Linux Technology Center
    IBM, ISTL
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