mm/mlock: stop counting mlocked pages when none vma is found

There will be no vma satisfies addr < vm_end when find_vma() returns NULL.
Thus it's meaningless to traverse the vma list below because we can't
find any vma to count mlocked pages.  Stop counting mlocked pages in this
case to save some vma list traversal cycles.

Link: https://lkml.kernel.org/r/20210204110705.17586-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mlock.c b/mm/mlock.c
index 73960bb..f8f8cc3 100644 (file)
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -622,7 +622,7 @@ static unsigned long count_mm_mlocked_page_nr(struct mm_struct *mm,
 
        vma = find_vma(mm, start);
        if (vma == NULL)
-               vma = mm->mmap;
+               return 0;
 
        for (; vma ; vma = vma->vm_next) {
                if (start >= vma->vm_end)