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    SubjectRe: [PATCH 4/4] Hugetlb: Copy on Write support
    On Wed, Nov 09, 2005 at 05:39:55PM -0600, Adam Litke wrote:
    > Hugetlb: Copy on Write support
    > Implement copy-on-write support for hugetlb mappings so MAP_PRIVATE can be
    > supported. This helps us to safely use hugetlb pages in many more
    > applications. The patch makes the following changes. If needed, I also have
    > it broken out according to the following paragraphs.
    > 1. Add a pair of functions to set/clear write access on huge ptes. The
    > writable check in make_huge_pte is moved out to the caller for use by COW
    > later.
    > 2. Hugetlb copy-on-write requires special case handling in the following
    > situations:
    > - copy_hugetlb_page_range() - Copied pages must be write protected so a COW
    > fault will be triggered (if necessary) if those pages are written to.
    > - find_or_alloc_huge_page() - Only MAP_SHARED pages are added to the page
    > cache. MAP_PRIVATE pages still need to be locked however.
    > 3. Provide hugetlb_cow() and calls from hugetlb_fault() and hugetlb_no_page()
    > which handles the COW fault by making the actual copy.
    > 4. Remove the check in hugetlbfs_file_map() so that MAP_PRIVATE mmaps will be
    > allowed. Make MAP_HUGETLB exempt from the depricated VM_RESERVED mapping
    > check.

    Did you do the audit of pte protection bits I asked about? If not, I'll
    dredge them up and check to make sure.

    -- wli
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