linux-kernel - Re: [PATCH][mm] adjust the logic of checking THP

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Date:	Wed, 2 Nov 2011 20:17:23 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Guanjun He <heguanbo@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH][mm] adjust the logic of checking THP

On Wed, Nov 2, 2011 at 2:34 PM, Guanjun He <heguanbo@...il.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@...il.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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