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    SubjectRe: [patch][v2] swap: virtual swap readahead
    Johannes Weiner wrote:
    > On Wed, Jun 03, 2009 at 01:34:57AM +0200, Andi Kleen wrote:
    >> On Wed, Jun 03, 2009 at 12:37:39AM +0200, Johannes Weiner wrote:

    >>> + pgd = pgd_offset(vma->vm_mm, pos);
    >>> + if (!pgd_present(*pgd))
    >>> + continue;
    >>> + pud = pud_offset(pgd, pos);
    >>> + if (!pud_present(*pud))
    >>> + continue;
    >>> + pmd = pmd_offset(pud, pos);
    >>> + if (!pmd_present(*pmd))
    >>> + continue;
    >>> + pte = pte_offset_map_lock(vma->vm_mm, pmd, pos, &ptl);
    >> You could be more efficient here by using the standard mm/* nested loop
    >> pattern that avoids relookup of everything in each iteration. I suppose
    >> it would mainly make a difference with 32bit highpte where mapping a pte
    >> can be somewhat costly. And you would take less locks this way.
    >
    > I ran into weird problems here. The above version is actually faster
    > in the benchmarks than writing a nested level walker or using
    > walk_page_range(). Still digging but it can take some time. Busy
    > week :(

    I'm not too worried about not walking the page tables,
    because swap is an extreme slow path anyway.

    --
    All rights reversed.


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