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    SubjectRe: [patch] mm: reduce pagetable-freeing latencies
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    On Wed, 2007-07-25 at 12:26 +0200, Andi Kleen wrote:
    > > Plan is fixed array or 4 or maybe 8 entries (pointers), that shouldn't
    > > be -too- bad. The code path I'm a bit worried about is
    >
    > Yep.
    >
    > > unmap_mapping_ranges() which goes into zapping page tables from deep
    > > within filesystems.
    >
    > Your aim is to conserve stack space?
    > The worst case has to work without overflow anyways, so using VLAs don't
    > help you. Just allocate the largest size you can safely afford.
    >
    > This is also easier to test; if it is too large it is better when
    > the overflow triggers always.
    >
    > They are more useful in user space with larger stacks when you don't
    > know the maximum size.

    In fact, i discussed with peter and I think the best is to only have one
    entry in the stack mmu_gather structure. If we fail to allocate a page
    to batch entries, we flush that one and steal it :-) Then we have a page
    to gather more.

    I'll give that a go tomorrow, I got delayed by some stupid HW issues
    today.

    Cheers,
    Ben.


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