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    SubjectRe: [PATCH][mm] adjust the logic of checking THP
    From
    On Wed, Nov 2, 2011 at 2:34 PM, Guanjun He <heguanbo@gmail.com> wrote:
    >
    > Acturally, pmd_trans_huge(orig_pmd) only checks the _PAGE_PSE bits,
    > it's a pmd entry bits, only mark a size, not a flag;As one can easily
    > create the same pmd entry bits for some special use,then the check
    > will get confused.And this patch is to adjust the logic to use the flag,
    > it can perfectly avoid this potential issuse,and basically no impact
    > to the current code.
    >
    >
    > Signed-off-by: Guanjun He <heguanbo@gmail.com>
    > ---
    >  mm/memory.c |   28 +++++++++++++++-------------
    >  1 files changed, 15 insertions(+), 13 deletions(-)
    >
    > diff --git a/mm/memory.c b/mm/memory.c
    > index a56e3ba..a76b17f 100644
    > --- a/mm/memory.c
    > +++ b/mm/memory.c
    > @@ -3465,20 +3465,22 @@ int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
    >        pmd = pmd_alloc(mm, pud, address);
    >        if (!pmd)
    >                return VM_FAULT_OOM;
    > -       if (pmd_none(*pmd) && transparent_hugepage_enabled(vma)) {
    > -               if (!vma->vm_ops)
    > -                       return do_huge_pmd_anonymous_page(mm, vma, address,
    > -                                                         pmd, flags);
    > -       } else {
    > -               pmd_t orig_pmd = *pmd;
    > -               barrier();
    > -               if (pmd_trans_huge(orig_pmd)) {
    > -                       if (flags & FAULT_FLAG_WRITE &&
    > -                           !pmd_write(orig_pmd) &&
    > -                           !pmd_trans_splitting(orig_pmd))
    > -                               return do_huge_pmd_wp_page(mm, vma, address,
    > -                                                          pmd, orig_pmd);
    > +       if (transparent_hugepage_enabled(vma)) {

    Well, how about THP not configured?

    Thanks,
    Hillf

    > +               if (pmd_none(*pmd)) {
    > +                       if (!vma->vm_ops)
    > +                               return do_huge_pmd_anonymous_page(mm, vma, address,
    > +                                                                 pmd, flags);
    > +               } else {
    > +                       pmd_t orig_pmd = *pmd;
    > +                       barrier();
    > +                       if (pmd_trans_huge(orig_pmd)) {
    > +                               if (flags & FAULT_FLAG_WRITE &&
    > +                                   !pmd_write(orig_pmd) &&
    > +                                   !pmd_trans_splitting(orig_pmd))
    > +                                       return do_huge_pmd_wp_page(mm, vma, address,
    > +                                                                  pmd, orig_pmd);
    >                        return 0;
    > +                       }
    >                }
    >        }
    >
    > --
    > 1.7.7
    >
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