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    SubjectRe: [Devel] Re: [ckrm-tech] [PATCH] BC: resource beancounters (v4) (added user memory)
    Rohit Seth wrote:
    > On Fri, 2006-09-15 at 13:26 +0400, Kirill Korotaev wrote:
    >
    > <...skipped...>
    >
    >> for VMware which can reserve required amount of RAM for VM.
    >>
    >
    > It is much easier to provide guarantees in complete virtual
    > environments. But then you pay the cost in terms of performance.
    >
    "Complete virtual environments" vs. "contaners" is not [only] about
    performance! In the end, given a proper set of dirty and no-so-dirty
    hacks in software and hardware, their performance will be close to native.

    Containers vs. other virtualization types is more about utilization,
    density, scalability, portability.

    Speaking of guarantees, yes, guarantees is easy, you just reserve such
    amount of RAM for your VM and that is all. But the fact is usually some
    part of that RAM will not be utilized by this particular VM. But since
    it is reserved, it can not be utilized by other VMs -- and we end up
    just wasting some resources. Containers, given a proper resource
    management and configuration, can have some guarantees and still be able
    to utilize all the RAM available in the system. This difference can be
    metaphorically expressed as a house divided into rooms. Dividing walls
    can either be hard or flexible. With flexible walls, room (container)
    owner have a guarantee of minimal space in your room, but if a few
    guests come for a moment, the walls can move to make more space (up to
    the limit). So the flexibility is measured as the delta between a
    guarantee and a limit.

    This flexibility leads to higher utilization, and this flexibility is
    one of the reasons for better density (a few times higher than that of a
    paravirtualization solution).

    I will not touch scalability and portability topics here to make things
    simpler.
    > I think we should punt on hard guarantees and fractions for the first
    > draft. Keep the implementation simple.
    >
    Do I understand it right that with hard guarantees we loose the
    flexibility I have just described? If this is the case, I do not like it.
    -
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