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    SubjectRe: [PATCH] hugetlb: call mmu notifiers on hugepage cow
    On Fri, May 28, 2010 at 09:39:59AM -0700, Doug Doan wrote:
    > On 05/28/2010 02:59 AM, Mel Gorman wrote:
    >> On Thu, May 27, 2010 at 01:43:00PM -0700, Doug Doan wrote:
    >>> From: Doug Doan<dougd@cray.com>
    >>>
    >>> When a copy-on-write occurs, we take one of two paths in handle_mm_fault:
    >>> through handle_pte_fault for normal pages, or through hugetlb_fault for
    >>> huge pages.
    >>>
    >>> In the normal page case, we eventually get to do_wp_page and call mmu
    >>> notifiers via ptep_clear_flush_notify. There is no callout to the mmmu
    >>> notifiers in the huge page case. This patch fixes that.
    >>>
    >>> Signed-off-by: Doug Doan<dougd@cray.com>
    >>> ---
    >>
    >>> --- mm/hugetlb.c.orig 2010-05-27 13:07:58.569546314 -0700
    >>> +++ mm/hugetlb.c 2010-05-26 14:41:06.449296524 -0700
    >>> @@ -2345,11 +2345,17 @@ retry_avoidcopy:
    >>> ptep = huge_pte_offset(mm, address& huge_page_mask(h));
    >>> if (likely(pte_same(huge_ptep_get(ptep), pte))) {
    >>> /* Break COW */
    >>> + mmu_notifier_invalidate_range_start(mm,
    >>> + address& huge_page_mask(h),
    >>> + (address& huge_page_mask(h)) + huge_page_size(h));
    >>
    >> Should the address not already be aligned?
    >
    > I'm not seeing where the address was aligned before this point. The code
    > just above aligns it:
    >
    > ptep = huge_pte_offset(mm, address& huge_page_mask(h));
    > if (likely(pte_same(huge_ptep_get(ptep), pte))) {
    > /* Break COW */
    >

    I'm sorry. You're right. I was looking at the copy_huge_page which was
    not aligning the address. It should be but it's ultimately harmless as
    the parameter is discarded.

    Acked-by: Mel Gorman <mel@csn.ul.ie>

    >> Otherwise, I don't see any problem.
    >>
    >>> huge_ptep_clear_flush(vma, address, ptep);
    >>> set_huge_pte_at(mm, address, ptep,
    >>> make_huge_pte(vma, new_page, 1));
    >>> /* Make the old page be freed below */
    >>> new_page = old_page;
    >>> + mmu_notifier_invalidate_range_end(mm,
    >>> + address& huge_page_mask(h),
    >>> + (address& huge_page_mask(h)) + huge_page_size(h));
    >>> }
    >>> page_cache_release(new_page);
    >>> page_cache_release(old_page);
    >>
    >>
    >

    --
    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab


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