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    SubjectRe: Change in functionality of futex() system call.
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    On Thu, 2011-06-09 at 20:37 +0900, KOSAKI Motohiro wrote:
    > 1) check the pte of the target address is RW attribute.
    > 2-1) if yes, it has no COW chance. we can safely use gup result.
    > 2-2) if no, we have to fallback slow vma walk. maybe, it's okey.
    > both RO mappings and COW are rare situation.

    Not so, clean file pages are RO, even if the vma is writable. We use the
    fault to track dirty state with.




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