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    SubjectRe: [PATCH] add a clear_pages function to clear pages of higher order
    Date
    On Friday 11 March 2005 03:03, Christoph Lameter wrote:
    > Changelog:
    > - use Kconfig and CONFIG_CLEAR_PAGES
    >
    > The zeroing of a page of a arbitrary order in page_alloc.c and in hugetlb.c may benefit from a
    > clear_page that is capable of zeroing multiple pages at once. The following patch adds
    > a function "clear_pages" that is capable of clearing multiple continuous pages at once.
    >
    > Patch against 2.6.11-bk6
    >
    > Signed-off-by: Christoph Lameter <clameter@sgi.com>
    [snip]
    > -clear_page_end:
    > +clear_pages_end:
    >
    > /* C stepping K8 run faster using the string instructions.
    > It is also a lot simpler. Use this when possible */

    Andi Kleen (iirc) says that non-temporal stores seem to be
    big win in microbenchmarks (and I second that), but they are
    a net loss when we are going to use zeroed page just after
    zeroing. He recommends avoid using non-temporal stores

    With this new page prezeroing infrastructure, that argument
    most likely is not right anymore. Especially clearing of
    high-order pages definitely will benefit from NT stores
    because they do not kill L1 data cache in the process.

    I don't have K8 and therefore cannot be 100% sure, but
    I really doubt that K8 optimize "rep stosq" into _NT_ stores.

    Andi?
    --
    vda

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