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    SubjectRe: VM Requirement Document - v0.0
    On Monday 02 July 2001 20:42, Rik van Riel wrote:
    > On Thu, 28 Jun 2001, Marco Colombo wrote:
    > > I'm not sure that, in general, recent pages with only one access are
    > > still better eviction candidates compared to 8 hours old pages. Here
    > > we need either another way to detect one-shot activity (like the one
    > > performed by updatedb),
    > Fully agreed, but there is one problem with this idea.
    > Suppose you have a maximum of 20% of your RAM for these
    > "one-shot" things, now how are you going to be able to
    > page in an application with a working set of, say, 25%
    > the size of RAM ?

    Easy. What's the definition of working set? Those pages that are frequently
    referenced. So as the application starts up some of its pages will get
    promoted from used-once to used-often. (On the other hand, the target
    behavior here conflicts with the goal of grouping together several
    temporally-related accesses to the same page together as one access, so
    there's a subtle distinction to be made here, see below.)

    The point here is that there are such things as run-once program pages, just
    as there are use-once file pages. Both should get low priority and be
    evicted early, regardless of the fact they were just loaded.

    > If you don't have any special measures, the pages from
    > this "new" application will always be treated as one-shot
    > pages and the process will never be able to be cached in
    > memory completely...

    The self-balancing way of doing this is to promote pages from the old end of
    the used-once list to the used-often (active) list at a rate corresponding to
    the fault-in rate so we get more aggressive promotion of referenced-often
    pages during program loading, and conversely, aggressive demotion of
    referenced-once pages.


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