On Fri 09-12-11 17:48:40, kosaki.motohiro@xxxxxxxxx wrote:
> From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
>
> 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.
>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> ---
> mm/mmap.c | 36 ++++++++----------------------------
> 1 files changed, 8 insertions(+), 28 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index eae90af..b9c0241 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1603,39 +1603,19 @@ 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)
> {
> - struct vm_area_struct *vma = NULL, *prev = NULL;
> - struct rb_node *rb_node;
> - if (!mm)
> - goto out;
> -
> - /* Guard against addr being lower than the first VMA */
> - vma = mm->mmap;
Why have you removed this guard? Previously we had pprev==NULL and
returned mm->mmap.
This seems like a semantic change without any explanation. Could you
clarify?
> -
> - /* Go through the RB tree quickly. */
> - rb_node = mm->mm_rb.rb_node;
> -
> - while (rb_node) {
> - struct vm_area_struct *vma_tmp;
> - vma_tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb);
> -
> - if (addr < vma_tmp->vm_end) {
> - rb_node = rb_node->rb_left;
> - } else {
> - prev = vma_tmp;
> - if (!prev->vm_next || (addr < prev->vm_next->vm_end))
> - break;
> - rb_node = rb_node->rb_right;
> - }
> - }
> + struct vm_area_struct *vma;
>
> -out:
> - *pprev = prev;
> - return prev ? prev->vm_next : vma;
> + vma = find_vma(mm, addr);
> + *pprev = vma ? vma->vm_prev : NULL;
> + return vma;
> }
>
> /*
> --
> 1.7.1
>
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--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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