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    SubjectRe: [PATCH 2/9] ksm: let shared pages be swappable
    On Fri, 4 Dec 2009 09:16:40 -0800
    Chris Wright <chrisw@redhat.com> wrote:

    > * KAMEZAWA Hiroyuki (kamezawa.hiroyu@jp.fujitsu.com) wrote:
    > > KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
    > > > Windows kernel have zero page thread and it clear the pages in free list
    > > > periodically. because many windows subsystem prerefer zero filled page.
    > > > hen, if we use windows guest, zero filled page have plenty mapcount rather
    > > > than other typical sharing pages, I guess.
    > > >
    > > > So, can we mark as unevictable to zero filled ksm page?
    >
    > That's why I mentioned the page of zeroes as the prime example of
    > something with a high mapcount that shouldn't really ever be evicted.
    >
    > > Hmm, can't we use ZERO_PAGE we have now ?
    > > If do so,
    > > - no mapcount check
    > > - never on LRU
    > > - don't have to maintain shared information because ZERO_PAGE itself has
    > > copy-on-write nature.
    >
    > It's a somewhat special case, but wouldn't it be useful to have a generic
    > method to recognize this kind of sharing since it's a generic issue?
    >

    I just remembered that why ZERO_PAGE was removed (in past). It was becasue
    cache-line ping-pong at fork beacause of page->mapcount. And KSM introduces
    zero-pages which have mapcount again. If no problems in realitsitc usage of
    KVM, ignore me.

    Thanks,
    -Kame



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