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    SubjectRe: [PATCH]: Handling spurious page fault for hugetlb region for 2.6.14-rc4-git5
    Hugh Dickins <hugh@veritas.com> wrote:
    >
    > On Wed, 19 Oct 2005, Rohit Seth wrote:
    > > On Wed, 2005-10-19 at 16:48 +0100, Hugh Dickins wrote:
    > > >
    > > > What happens when the hugetlb file is truncated down and back up after
    > > > the mmap? Truncating down will remove a page from the mmap and flush TLB.
    > > > Truncating up will let accesses to the gone page pass the valid...off test.
    > > > But we've no support for hugetlb faulting in this version: so won't it get
    > > > get stuck in a tight loop?
    > >
    > > First of all, there is currently no support of extending the hugetlb
    > > file size using truncate in 2.6.14. (I agree that part is broken). So
    > > the above scenario can not happen.
    >
    > I was forgetting that extending ftruncate wasn't supported in 2.6.14 and
    > earlier, yes. But I'm afraid the above scenario can still happen there:
    > extending is done, not by ftruncate, but by (somewhere else) mmapping the
    > larger size. So your fix may still cause a tight infinite fault loop.

    Will it? Whenever we mmap a hugetlbfs file we prepopulate the entire vma
    with hugepages. So I don't think there's ever any part of an address space
    which ia a) inside a hugepage vma and b) doesn't have a hugepage backing
    it.
    -
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