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    SubjectRe: [RFC PATCH 0/5] Use an alternative to _PAGE_PROTNONE for _PAGE_NUMA v2
    On Tue, Apr 08, 2014 at 07:30:31PM +0200, Peter Zijlstra wrote:
    > On Tue, Apr 08, 2014 at 05:46:52PM +0100, Mel Gorman wrote:
    > > Someone will ask why automatic NUMA balancing hints do not use "real"
    > > PROT_NONE but as it would need VMA information to do that on all
    > > architectures it would mean that VMA-fixups would be required when marking
    > > PTEs for NUMA hinting faults so would be expensive.
    >
    > Like this:
    >
    > https://lkml.org/lkml/2012/11/13/431
    >
    > That used the generic PROT_NONE infrastructure and compared, on fault,
    > the page protection bits against the vma->vm_page_prot bits?
    >
    > So the objection to that approach was the vma-> dereference in
    > pte_numa() ?

    Peter, I somehow missing, with this patch would it be possible to
    get rid of ugly macros in 2 level pages like we have now? (I've
    dropped off softdirty support for non x86-64 now [patches are
    flying around]) but still there are a few remains which make
    Linus unhappy.

    static __always_inline pgoff_t pte_to_pgoff(pte_t pte)
    {
    return (pgoff_t)
    (pte_bitop(pte.pte_low, PTE_FILE_SHIFT1, PTE_FILE_MASK1, 0) +
    pte_bitop(pte.pte_low, PTE_FILE_SHIFT2, PTE_FILE_MASK2, PTE_FILE_LSHIFT2) +
    pte_bitop(pte.pte_low, PTE_FILE_SHIFT3, -1UL, PTE_FILE_LSHIFT3));
    }


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