On Fri, 2011-12-09 at 16:23 -0500, kosaki.motohiro@xxxxxxxxx wrote:
> commit 297c5eee37 (mm: make the vma list be doubly linked) added
> vm_prev member into vm_area_struct. Therefore we can simplify
> find_vma_prev() by using it. Also, this change help to improve
> page fault performance because it has strong locality of reference.
trivia:
> diff --git a/mm/mmap.c b/mm/mmap.c
[]
> @@ -1603,39 +1603,21 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
>
> EXPORT_SYMBOL(find_vma);
>
> -/* Same as find_vma, but also return a pointer to the previous VMA in *pprev. */
> +/*
> + * Same as find_vma, but also return a pointer to the previous VMA in *pprev.
> + * Note: pprev is set to NULL when return value is NULL.
> + */
> struct vm_area_struct *
> -find_vma_prev(struct mm_struct *mm, unsigned long addr,
> - struct vm_area_struct **pprev)
> +find_vma_prev(struct mm_struct *mm, unsigned long addr, struct vm_area_struct **pprev)
eh. This declaration change seems gratuitous and it exceeds 80 columns.
> + *pprev = NULL;
> + vma = find_vma(mm, addr);
> + if (vma)
> + *pprev = vma->vm_prev;
There's no need to possibly set *pprev twice.
Maybe
{
struct vm_area_struct *vma = find_vma(mm, addr);
*pprev = vma ? vma->vm_prev : NULL;
or
if (vma)
*pprev = vma->vm_prev;
else
*pprev = NULL;
return vma;
}
> -out:
> - *pprev = prev;
> - return prev ? prev->vm_next : vma;
> + return vma;
> }
>
> /*
--
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