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    SubjectRe: [PATCH 00/03] Unmapped: Separate unmapped and mapped pages
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    On Fri, 2006-03-10 at 14:38 +0100, Magnus Damm wrote:
    > On 3/10/06, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

    > > Breaking the LRU in two like this breaks the page ordering, which makes
    > > it possible for pages to stay resident even though they have much less
    > > activity than pages that do get reclaimed.
    >
    > Yes, true. But this happens already with a per-zone LRU. LRU pages
    > that happen to end up in the DMA zone will probably stay there a
    > longer time than pages in the normal zone. That does not mean it is
    > right to break the page ordering though, I'm just saying it happens
    > already and the oldest piece of data in the global system will not be
    > reclaimed first - instead there are priorities such as unmapped pages
    > will be reclaimed over mapped and so on. (I strongly feel that there
    > should be per-node LRU:s, but that's another story)

    If reclaim works right* there is equal pressure on each zone
    (proportional to their size) and hence each page will have an equal life
    time expectancy.

    (*) this is of course not possible for all workloads, however
    balance_pgdat and the page allocator take pains to make it as true as
    possible.

    Peter

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