Subject: migrate anon_vma refcount methods

From: Andrea Arcangeli <aarcange@redhat.com>

Adapt migrate to use anon_vma refcount methods.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---

diff --git a/mm/migrate.c b/mm/migrate.c
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -639,7 +639,7 @@ static int unmap_and_move(new_page_t get
 			 * exist when the page is remapped later
 			 */
 			anon_vma = page_anon_vma(page);
-			atomic_inc(&anon_vma->external_refcount);
+			get_anon_vma(anon_vma);
 		}
 	}
 
@@ -682,12 +682,8 @@ skip_unmap:
 rcu_unlock:
 
 	/* Drop an anon_vma reference if we took one */
-	if (anon_vma && atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->lock)) {
-		int empty = list_empty(&anon_vma->head);
-		spin_unlock(&anon_vma->lock);
-		if (empty)
-			anon_vma_free(anon_vma);
-	}
+	if (anon_vma)
+		drop_anon_vma(anon_vma);
 
 	if (rcu_locked)
 		rcu_read_unlock();