linux-kernel - Re: [PATCH] mm: code improvement of check_stack_guard

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Message-ID: <AANLkTi=wy07mZE=h1JSq9GN8_d0taikw5zMfMh+iqFWL@mail.gmail.com>
Date:	Wed, 18 Aug 2010 11:40:28 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	jovi zhang <bookjovi@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: code improvement of check_stack_guard_page

On Sun, Aug 15, 2010 at 10:45 AM, jovi zhang <bookjovi@...il.com> wrote:
> little code improvement of check_stack_guard_page function.
> this commit is on top of commit "mm: keep a guard page below a
> grow-down stack segment" of linus.
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 9b3b73f..643b112 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2768,13 +2768,15 @@ out_release:
>   */
>  static inline int check_stack_guard_page(struct vm_area_struct *vma,
> unsigned long address)
>  {
> -       address &= PAGE_MASK;
> -       if ((vma->vm_flags & VM_GROWSDOWN) && address == vma->vm_start) {
> -               address -= PAGE_SIZE;
> -               if (find_vma(vma->vm_mm, address) != vma)
> -                       return -ENOMEM;
> -
> -               expand_stack(vma, address);
> +       if (vma->vm_flags & VM_GROWSDOWN) {
> +               address &= PAGE_MASK;
> +               if(address == vma->vm_start) {
                    ^^^ coding style is broken, did u run it through
scripts/checkpatch.pl?

> +                       address -= PAGE_SIZE;
> +                       if (unlikely(find_vma(vma->vm_mm, address) != vma))
> +                               return -ENOMEM;
> +
> +                       expand_stack(vma, address);
> +               }
>         }
>         return 0;
>  }
>

The main benefit I see is the new branch hint being passed to
find_vma, is my understanding correct?

Balbir
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