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    Subject[PATCH 4/4] anonvma: when setting up page->mapping, we need to pick the _oldest_ anonvma

    From: Linus Torvalds <>
    Date: Mon, 12 Apr 2010 12:44:29 -0700
    Subject: [PATCH 4/4] anonvma: when setting up page->mapping, we need to pick the _oldest_ anonvma

    Otherwise we might be mapping in a page in a new mapping, but that page
    (through the swapcache) would later be mapped into an old mapping too.
    The page->mapping must be the case that works for everybody, not just
    the mapping that happened to page it in first.

    This can be improved in certain cases: if we know the page is private to
    just this particular mapping (for example, it's a new page, or it is the
    only swapcache entry), we could pick the top (most specific) anon_vma.

    But that's a future optimization. Make it _work_ reliably first.

    Signed-off-by: Linus Torvalds <>
    mm/rmap.c | 15 +++++++++++++--
    1 files changed, 13 insertions(+), 2 deletions(-)

    diff --git a/mm/rmap.c b/mm/rmap.c
    index ee97d38..4bad326 100644
    --- a/mm/rmap.c
    +++ b/mm/rmap.c
    @@ -734,9 +734,20 @@ void page_move_anon_rmap(struct page *page,
    static void __page_set_anon_rmap(struct page *page,
    struct vm_area_struct *vma, unsigned long address)
    - struct anon_vma *anon_vma = vma->anon_vma;
    + struct anon_vma_chain *avc;
    + struct anon_vma *anon_vma;
    + BUG_ON(!vma->anon_vma);
    + /*
    + * We must use the _oldest_ possible anon_vma for the page mapping!
    + *
    + * So take the last AVC chain entry in the vma, which is the deepest
    + * ancestor, and use the anon_vma from that.
    + */
    + avc = list_entry(vma->anon_vma_chain.prev, struct anon_vma_chain, same_vma);
    + anon_vma = avc->anon_vma;

    - BUG_ON(!anon_vma);
    anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
    page->mapping = (struct address_space *) anon_vma;
    page->index = linear_page_index(vma, address);

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