---
 include/linux/rmap.h |   14 +-------------
 mm/migrate.c         |    4 ++--
 mm/rmap.c            |   41 ++++++++++++++++++++---------------------
 3 files changed, 23 insertions(+), 36 deletions(-)

Index: linux-2.6/include/linux/rmap.h
===================================================================
--- linux-2.6.orig/include/linux/rmap.h	2008-03-22 00:12:50.000000000 -0700
+++ linux-2.6/include/linux/rmap.h	2008-03-22 00:12:58.000000000 -0700
@@ -26,7 +26,6 @@
  */
 struct anon_vma {
 	struct rw_semaphore sem;/* Serialize access to vma list */
-	atomic_t refcount;	/* vmas on the list */
 	struct list_head head;	/* List of private "related" vmas */
 };
 
@@ -44,18 +43,7 @@ static inline void anon_vma_free(struct 
 	kmem_cache_free(anon_vma_cachep, anon_vma);
 }
 
-struct anon_vma *grab_anon_vma(struct page *page);
-
-static inline void get_anon_vma(struct anon_vma *anon_vma)
-{
-	atomic_inc(&anon_vma->refcount);
-}
-
-static inline void put_anon_vma(struct anon_vma *anon_vma)
-{
-	if (atomic_dec_and_test(&anon_vma->refcount))
-		anon_vma_free(anon_vma);
-}
+struct anon_vma *page_lock_anon_vma(struct page *page);
 
 static inline void anon_vma_lock(struct vm_area_struct *vma)
 {
Index: linux-2.6/mm/migrate.c
===================================================================
--- linux-2.6.orig/mm/migrate.c	2008-03-22 00:12:50.000000000 -0700
+++ linux-2.6/mm/migrate.c	2008-03-22 00:12:58.000000000 -0700
@@ -655,7 +655,7 @@ static int unmap_and_move(new_page_t get
 	 * just care Anon page here.
 	 */
 	if (PageAnon(page))
-		anon_vma = grab_anon_vma(page);
+		anon_vma = page_lock_anon_vma(page);
 
 	/*
 	 * Corner case handling:
@@ -695,7 +695,7 @@ static int unmap_and_move(new_page_t get
  		mem_cgroup_end_migration(newpage);
 rcu_unlock:
 	if (anon_vma)
-		put_anon_vma(anon_vma);
+		up_read(&anon_vma->sem);
 
 unlock:
 
Index: linux-2.6/mm/rmap.c
===================================================================
--- linux-2.6.orig/mm/rmap.c	2008-03-22 00:12:50.000000000 -0700
+++ linux-2.6/mm/rmap.c	2008-03-22 00:12:58.000000000 -0700
@@ -80,7 +80,6 @@ int anon_vma_prepare(struct vm_area_stru
 		/* page_table_lock to protect against threads */
 		spin_lock(&mm->page_table_lock);
 		if (likely(!vma->anon_vma)) {
-			get_anon_vma(anon_vma);
 			vma->anon_vma = anon_vma;
 			list_add_tail(&vma->anon_vma_node, &anon_vma->head);
 			allocated = NULL;
@@ -99,17 +98,14 @@ void __anon_vma_merge(struct vm_area_str
 {
 	BUG_ON(vma->anon_vma != next->anon_vma);
 	list_del(&next->anon_vma_node);
-	put_anon_vma(vma->anon_vma);
 }
 
 void __anon_vma_link(struct vm_area_struct *vma)
 {
 	struct anon_vma *anon_vma = vma->anon_vma;
 
-	if (anon_vma) {
-		get_anon_vma(anon_vma);
+	if (anon_vma)
 		list_add_tail(&vma->anon_vma_node, &anon_vma->head);
-	}
 }
 
 void anon_vma_link(struct vm_area_struct *vma)
@@ -117,7 +113,6 @@ void anon_vma_link(struct vm_area_struct
 	struct anon_vma *anon_vma = vma->anon_vma;
 
 	if (anon_vma) {
-		get_anon_vma(anon_vma);
 		down_write(&anon_vma->sem);
 		list_add_tail(&vma->anon_vma_node, &anon_vma->head);
 		up_write(&anon_vma->sem);
@@ -127,14 +122,19 @@ void anon_vma_link(struct vm_area_struct
 void anon_vma_unlink(struct vm_area_struct *vma)
 {
 	struct anon_vma *anon_vma = vma->anon_vma;
+	int empty;
 
 	if (!anon_vma)
 		return;
 
 	down_write(&anon_vma->sem);
 	list_del(&vma->anon_vma_node);
+	/* We must garbage collect the anon_vma if it's empty */
+	empty = list_empty(&anon_vma->head);
 	up_write(&anon_vma->sem);
-	put_anon_vma(anon_vma);
+
+	if (empty)
+		anon_vma_free(anon_vma);
 }
 
 static void anon_vma_ctor(struct kmem_cache *cachep, void *data)
@@ -142,7 +142,6 @@ static void anon_vma_ctor(struct kmem_ca
 	struct anon_vma *anon_vma = data;
 
 	init_rwsem(&anon_vma->sem);
-	atomic_set(&anon_vma->refcount, 0);
 	INIT_LIST_HEAD(&anon_vma->head);
 }
 
@@ -156,11 +155,13 @@ void __init anon_vma_init(void)
  * Getting a lock on a stable anon_vma from a page off the LRU is
  * tricky: page_lock_anon_vma rely on RCU to guard against the races.
  */
-struct anon_vma *grab_anon_vma(struct page *page)
+struct anon_vma *page_lock_anon_vma(struct page *page)
 {
-	struct anon_vma *anon_vma = NULL;
+	struct anon_vma *anon_vma;
 	unsigned long anon_mapping;
 
+retry:
+	anon_vma = NULL;
 	rcu_read_lock();
 	anon_mapping = (unsigned long) page->mapping;
 	if (!(anon_mapping & PAGE_MAPPING_ANON))
@@ -169,26 +170,24 @@ struct anon_vma *grab_anon_vma(struct pa
 		goto out;
 
 	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
-	if (!atomic_inc_not_zero(&anon_vma->refcount))
+	if (unlikely(!down_read_trylock(&anon_vma->sem))) {
+		/* We behave like a spinlock here sigh... */
+		rcu_read_unlock();
+		cpu_relax();
+		goto retry;
+	}
+	if (list_empty(&anon_vma->head)) {
+		up_read(&anon_vma->sem);
 		anon_vma = NULL;
+	}
 out:
 	rcu_read_unlock();
 	return anon_vma;
 }
 
-static struct anon_vma *page_lock_anon_vma(struct page *page)
-{
-	struct anon_vma *anon_vma = grab_anon_vma(page);
-
-	if (anon_vma)
-		down_read(&anon_vma->sem);
-	return anon_vma;
-}
-
 static void page_unlock_anon_vma(struct anon_vma *anon_vma)
 {
 	up_read(&anon_vma->sem);
-	put_anon_vma(anon_vma);
 }
 
 /*