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    SubjectRe: [PATCH] mm: per-thread vma caching
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    On Thu, Feb 20, 2014 at 9:28 PM, Davidlohr Bueso <davidlohr@hp.com> wrote:
    > From: Davidlohr Bueso <davidlohr@hp.com>
    >
    > This patch is a continuation of efforts trying to optimize find_vma(),
    > avoiding potentially expensive rbtree walks to locate a vma upon faults.

    Ok, so I like this one much better than the previous version.

    However, I do wonder if the per-mm vmacache is actually worth it.
    Couldn't the per-thread one replace it entirely?

    Also, the hash you use for the vmacache index is *particularly* odd.

    int idx = (addr >> 10) & 3;

    you're using the top two bits of the address *within* the page.
    There's a lot of places that round addresses down to pages, and in
    general it just looks really odd to use an offset within a page as an
    index, since in some patterns (linear accesses, whatever), the page
    faults will always be to the beginning of the page, so index 0 ends up
    being special.

    What am I missing?

    Linus


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