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    SubjectRe: [patch 1/2] x86_64 page fault NMI-safe
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    On Wed, Jul 14, 2010 at 4:09 PM, Andi Kleen <andi@firstfloor.org> wrote:
    >
    > It can happen in theory, but for such a rare case take a lock
    > and walking everything should be fine.

    Actually, that's _exactly_ the wrong kind of thinking.

    Bad latency is bad latency, even when it happens rarely. So latency
    problems kill - even when they are rare. So you want to avoid them.
    And walking every possible page table is a _huge_ latency problem when
    it happens.

    In contrast, what's the advantage of doing thigns synchronously while
    holding a lock? It's that you can avoid a few page faults, and get
    better CPU use. But that's _stupid_ if it's something that is very
    rare to begin with.

    So the very rarity argues for the lazy approach. If it wasn't rare,
    there would be a much stronger argument for trying to do things
    up-front.

    Linus


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