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    SubjectRe: [rfc] increase struct page size?!
    On Fri, May 18, 2007 at 10:42:30AM +0100, David Howells wrote:
    > Nick Piggin <npiggin@suse.de> wrote:
    >
    > > I'd like to be the first to propose an increase to the size of struct page
    > > just for the sake of increasing it!
    >
    > Heh. I'm surprised you haven't got more adverse reactions.
    >
    > > If we add 8 bytes to struct page on 64-bit machines, it becomes 64 bytes,
    > > which is quite a nice number for cache purposes.
    >
    > Whilst that's true, if you have to deal with a run of contiguous page structs
    > (eg: the page allocator, perhaps) it's actually less efficient because it
    > takes more cache to do it. But, hey, it's a compromise whatever.
    >
    > In the scheme of things, if we're mostly dealing with individual page structs
    > (as I think we are), then yes, I think it's probably a good thing to do -
    > especially with larger page sizes.

    Yeah, we would end up eating about 12.5% more cachelines for contiguous
    runs of pages... but that only kicks in after we've touched 8 of them I
    think, and by that point the accesses should be very prefetchable.

    I think the average of 75% more cachelines touched for random accesses
    is going to outweigh the contiguous batch savings, but that's just a
    guess at this point.
    -
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