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    SubjectRe: [Patch 3/3] prepopulate/cache cleared pages
    Date
    On Thursday 23 February 2006 10:29, Arjan van de Ven wrote:
    > This patch adds an entry for a cleared page to the task struct. The main
    > purpose of this patch is to be able to pre-allocate and clear a page in a
    > pagefault scenario before taking any locks (esp mmap_sem),
    > opportunistically. Allocating+clearing a page is an very expensive
    > operation that currently increases lock hold times quite bit (in a threaded
    > environment that allocates/use/frees memory on a regular basis, this leads
    > to contention).
    >
    > This is probably the most controversial patch of the 3, since there is
    > a potential to take up 1 page per thread in this cache. In practice it's
    > not as bad as it sounds (a large degree of the pagefaults are anonymous
    > and thus immediately use up the page). One could argue "let the VM reap
    > these" but that has a few downsides; it increases locking needs but more,
    > clearing a page is relatively expensive, if the VM reaps the page again
    > in case it wasn't needed, the work was just wasted.

    Looks like an incredible bad hack. What workload was that again where it helps?
    And how much? I think before we can consider adding that ugly code you would a far better
    rationale.

    -Andi

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