On Tue, Aug 06, 2019 at 10:58:22AM +0000, Balbir Singh wrote:
>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
>
My bad, it should be
*pprev = !rb_node ? NULL
: rb_entry(rb_node, struct vm_area_struct, vm_rb);
Thanks
>Balbir Singh
--
Wei Yang
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