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    SubjectRe: [PATCH 1/2] thp: Add compound tail page _mapcount when mapped
    > > > Is the patch also applicable to 3.1.x?
    > >
    > > I suspect it's broken since many kernels back, at least since THP
    > > was introduced, maybe earlier.
    > Correct. And the other patch in this series if applied without the
    > above too, would make things worse for earlier releases (it'd trigger
    > the lack of above at first invocation instead of from the second by
    > having the _count start at 0 instead of 1, so it'd go negative at the
    > first put_page). The correct thing is to have _count start at 0, but
    > to increase it with the above during gup_fast (or to increase
    > _mapcount since 3.2-rc and leave _count at 0 at all times on tail
    > pages). Both patches should be ok for earlier releases too but I think
    > it's just a false positive that goes away with DEBUG_VM=n or we should
    > have noticed sooner (all production systems runs with DEBUG_VM=n of
    > course). If there is no problem with DEBUG_VM=n like it seems from the
    > source, I doubt it needs backporting. Also worst case a VM_BUG_ON
    > hits, there's no risk of memory corruption because the refcounting on
    > the head pages has always been correct, and that's all it matters
    > as far as hugetlbfs is concerned.

    I notice 70b50f94f1644e2aa7cb374819cfd93f3c28d725 "mm: thp: tail page
    refcounting fix" is in kernel 3.1.1 stable, so this series patches can be also
    applied to 3.1 stable.

    I expect the patch 70b50f94f1644e2aa7cb374819cfd93f3c28d725 also go to
    3.0 stable, so this series patches also applied to 3.0 stable.


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