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: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 28 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index adea3b8880e3..3f758c7f4c81 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;
-
-        /* 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;
 }
 
 /*