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    SubjectRe: [patch 11/21] Xen-paravirt: Add apply_to_page_range() which applies a function to a pte range.
    Andrew Morton wrote:
    > On Thu, 15 Feb 2007 18:25:00 -0800 Jeremy Fitzhardinge <> wrote:
    >>Add a new mm function apply_to_page_range() which applies a given
    >>function to every pte in a given virtual address range in a given mm
    >>structure. This is a generic alternative to cut-and-pasting the Linux
    >>idiomatic pagetable walking code in every place that a sequence of
    >>PTEs must be accessed.
    >>Although this interface is intended to be useful in a wide range of
    >>situations, it is currently used specifically by several Xen
    >>subsystems, for example: to ensure that pagetables have been allocated
    >>for a virtual address range, and to construct batched special
    >>pagetable update requests to map I/O memory (in ioremap()).
    > There was some discussion about this sort of thing last week. The
    > consensus was that it's better to run the callback against a whole pmd's
    > worth of ptes, mainly to amortise the callback's cost (a lot).
    > It was implemented in

    Speaking of that patch, I missed the discussion, but I'd hope it doesn't
    go upstream in its current form.

    We now have one way of walking range of ptes. The code may be duplicated a
    few times, but it is simple, we know how it works, and it is easy to get
    right because everyone does the same thing.

    We used to have about a dozen slightly different ways of doing this until
    Hugh spent the effort to standardise it all. Isn't it nice?

    If we want an ever-so-slightly lower performing interface for those paths
    that don't care to count every cycle -- which I think is a fine idea BTW
    -- it should be implemented in mm/memory.c and it should use our standard
    form of pagetable walking.

    SUSE Labs, Novell Inc.
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