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    SubjectRe: [RFC][PATCH 2/7] RSS controller core
    > On Mon, 12 Mar 2007 23:41:29 +0100 Herbert Poetzl <> wrote:
    > On Mon, Mar 12, 2007 at 11:42:59AM -0700, Dave Hansen wrote:
    > > How about we drill down on these a bit more.
    > >
    > > On Mon, 2007-03-12 at 02:00 +0100, Herbert Poetzl wrote:
    > > > - shared mappings of 'shared' files (binaries
    > > > and libraries) to allow for reduced memory
    > > > footprint when N identical guests are running
    > >
    > > So, it sounds like this can be phrased as a requirement like:
    > >
    > > "Guests must be able to share pages."
    > >
    > > Can you give us an idea why this is so?
    > sure, one reason for this is that guests tend to
    > be similar (or almost identical) which results
    > in quite a lot of 'shared' libraries and executables
    > which would otherwise get cached for each guest and
    > would also be mapped for each guest separately

    nooooooo. What you're saying there amounts to text replication. There is
    no proposal here to create duplicated copies of pagecache pages: the VM
    just doesn't support that (Nick has soe protopatches which do this as a
    possible NUMA optimisation).

    So these mmapped pages will contiue to be shared across all guests. The
    problem boils down to "which guest(s) get charged for each shared page".

    A simple and obvious and easy-to-implement answer is "the guest which paged
    it in". I think we should firstly explain why that is insufficient.

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