mm: simplify find_vma_prev()

commit 297c5eee37 ("mm: make the vma list be doubly linked") added the
vm_prev member to vm_area_struct.  We can simplify find_vma_prev() by
using it.  Also, this change helps to improve page fault performance
because it has stronger locality of reference.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Shaohua Li <shaohua.li@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index be0d6066b7dbc1baa6535a19fc115a92997b7b72..82e90ab3ecea0b449e4b1d501ffd95b962ab654c 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1626,39 +1626,21 @@ 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)
 {
-       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;
-
-       /* 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);
+       struct vm_area_struct *vma;
 
-               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;
-               }
-       }
+       *pprev = NULL;
+       vma = find_vma(mm, addr);
+       if (vma)
+               *pprev = vma->vm_prev;
 
-out:
-       *pprev = prev;
-       return prev ? prev->vm_next : vma;
+       return vma;
 }
 
 /*