On Tue, Aug 06, 2019 at 04:11:23PM +0800, Wei Yang wrote:
> When addr is out of the range of the whole rb_tree, pprev will points to
> the biggest node. find_vma_prev gets is by going through the right most
> node of the tree.
>
> Since only the last node is the one it is looking for, it is not
> necessary to assign pprev to those middle stage nodes. By assigning
> pprev to the last node directly, it tries to improve the function
> locality a little.
>
> Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
> ---
> mm/mmap.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 7e8c3e8ae75f..284bc7e51f9c 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2271,11 +2271,10 @@ find_vma_prev(struct mm_struct *mm, unsigned long addr,
> *pprev = vma->vm_prev;
> } else {
> struct rb_node *rb_node = mm->mm_rb.rb_node;
> - *pprev = NULL;
> - while (rb_node) {
> - *pprev = rb_entry(rb_node, struct vm_area_struct, vm_rb);
> + while (rb_node && rb_node->rb_right)
> rb_node = rb_node->rb_right;
> - }
> + *pprev = rb_node ? NULL
> + : rb_entry(rb_node, struct vm_area_struct, vm_rb);
Can rb_node ever be NULL? assuming mm->mm_rb.rb_node is not NULL when we
enter here
Balbir Singh
