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    SubjectRe: [PATCH] Allow preemption during lazy mmu updates
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    On Fri, 2009-03-27 at 11:02 -0700, Jeremy Fitzhardinge wrote:
    > Hi all,
    >
    > We discussed this series a while ago. The specific problem
    > was the need to disable preemption in apply_to_pte_range when using
    > lazy mmu updates around the callback function. When used on usermode
    > addresses there was no problem because it needs to take the pte
    > lock anyway, but there's no requirement for taking a pte lock when
    > updating kernel ptes, so it ended up adding a new no-preempt region.
    >
    > The gist of the series is that if we get preempted while doing an mmu
    > update, we flush all the pending updates and switch to the next task.
    > We record that the task was doing a lazy mmu update in its task flags,
    > and resume lazy updates when we switch back.
    >
    > All the context-switch time activity happens in the existing
    > context-switch pvops calls, so there's no cost to non-pvops systems,
    > or to pvops backends which don't use lazy mmu updates.
    >
    > I don't think there were any objections to this series, but Ingo would
    > like to see an Acked by from someone since it gets into the mm side
    > of things.
    >
    > (The first patch in the series adds the required preempt disable/enable
    > and then the rest of the series removes them again. I think the first
    > patch is already in mm-.)

    Looks good from my POV

    Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>



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