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    SubjectRe: [RFC/T/D][PATCH 2/2] Linux/Guest cooperative unmapped page cache control
    * Dave Hansen <dave@linux.vnet.ibm.com> [2010-06-14 10:09:31]:

    > On Mon, 2010-06-14 at 22:28 +0530, Balbir Singh wrote:
    > > If you've got duplicate pages and you know
    > > that they are duplicated and can be retrieved at a lower cost, why
    > > wouldn't we go after them first?
    >
    > I agree with this in theory. But, the guest lacks the information about
    > what is truly duplicated and what the costs are for itself and/or the
    > host to recreate it. "Unmapped page cache" may be the best proxy that
    > we have at the moment for "easy to recreate", but I think it's still too
    > poor a match to make these patches useful.
    >

    That is why the policy (in the next set) will come from the host. As
    to whether the data is truly duplicated, my experiments show up to 60%
    of the page cache is duplicated. The first patch today is again
    enabled by the host. Both of them are expected to be useful in the
    cache != none case.

    The data I have shows more details including the performance and
    overhead.

    --
    Three Cheers,
    Balbir


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