4 files changed, 24 insertions, 40 deletions

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 567d43f29a10..77216742c178 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -26,11 +26,17 @@
  */
 struct anon_vma {
         spinlock_t lock;        /* Serialize access to vma list */
-#ifdef CONFIG_KSM
-        atomic_t ksm_refcount;
-#endif
-#ifdef CONFIG_MIGRATION
-        atomic_t migrate_refcount;
+#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
+
+        /*
+         * The external_refcount is taken by either KSM or page migration
+         * to take a reference to an anon_vma when there is no
+         * guarantee that the vma of page tables will exist for
+         * the duration of the operation. A caller that takes
+         * the reference is responsible for clearing up the
+         * anon_vma if they are the last user on release
+         */
+        atomic_t external_refcount;
 #endif
         /*
          * NOTE: the LSB of the head.next is set by
@@ -64,46 +70,26 @@ struct anon_vma_chain {
 };
 
 #ifdef CONFIG_MMU
-#ifdef CONFIG_KSM
-static inline void ksm_refcount_init(struct anon_vma *anon_vma)
+#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
+static inline void anonvma_external_refcount_init(struct anon_vma *anon_vma)
 {
-        atomic_set(&anon_vma->ksm_refcount, 0);
+        atomic_set(&anon_vma->external_refcount, 0);
 }
 
-static inline int ksm_refcount(struct anon_vma *anon_vma)
+static inline int anonvma_external_refcount(struct anon_vma *anon_vma)
 {
-        return atomic_read(&anon_vma->ksm_refcount);
+        return atomic_read(&anon_vma->external_refcount);
 }
 #else
-static inline void ksm_refcount_init(struct anon_vma *anon_vma)
+static inline void anonvma_external_refcount_init(struct anon_vma *anon_vma)
 {
 }
 
-static inline int ksm_refcount(struct anon_vma *anon_vma)
+static inline int anonvma_external_refcount(struct anon_vma *anon_vma)
 {
         return 0;
 }
 #endif /* CONFIG_KSM */
-#ifdef CONFIG_MIGRATION
-static inline void migrate_refcount_init(struct anon_vma *anon_vma)
-{
-        atomic_set(&anon_vma->migrate_refcount, 0);
-}
-
-static inline int migrate_refcount(struct anon_vma *anon_vma)
-{
-        return atomic_read(&anon_vma->migrate_refcount);
-}
-#else
-static inline void migrate_refcount_init(struct anon_vma *anon_vma)
-{
-}
-
-static inline int migrate_refcount(struct anon_vma *anon_vma)
-{
-        return 0;
-}
-#endif /* CONFIG_MIGRATE */
 
 static inline struct anon_vma *page_anon_vma(struct page *page)
 {
diff --git a/mm/ksm.c b/mm/ksm.c
index 956880f2ff49..6c3e99b4ae7c 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -318,14 +318,14 @@ static void hold_anon_vma(struct rmap_item *rmap_item,
                           struct anon_vma *anon_vma)
 {
         rmap_item->anon_vma = anon_vma;
-        atomic_inc(&anon_vma->ksm_refcount);
+        atomic_inc(&anon_vma->external_refcount);
 }
 
 static void drop_anon_vma(struct rmap_item *rmap_item)
 {
         struct anon_vma *anon_vma = rmap_item->anon_vma;
 
-        if (atomic_dec_and_lock(&anon_vma->ksm_refcount, &anon_vma->lock)) {
+        if (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)
diff --git a/mm/migrate.c b/mm/migrate.c
index b768a1d4fa43..42a3d24d1107 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -601,7 +601,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
                 rcu_read_lock();
                 rcu_locked = 1;
                 anon_vma = page_anon_vma(page);
-                atomic_inc(&anon_vma->migrate_refcount);
+                atomic_inc(&anon_vma->external_refcount);
         }
 
         /*
@@ -643,7 +643,7 @@ skip_unmap:
 rcu_unlock:
 
         /* Drop an anon_vma reference if we took one */
-        if (anon_vma && atomic_dec_and_lock(&anon_vma->migrate_refcount, &anon_vma->lock)) {
+        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)
diff --git a/mm/rmap.c b/mm/rmap.c
index f522cb008646..b5c320f7d0a5 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -250,8 +250,7 @@ static void anon_vma_unlink(struct anon_vma_chain *anon_vma_chain)
         list_del(&anon_vma_chain->same_anon_vma);
 
         /* We must garbage collect the anon_vma if it's empty */
-        empty = list_empty(&anon_vma->head) && !ksm_refcount(anon_vma) &&
-                                        !migrate_refcount(anon_vma);
+        empty = list_empty(&anon_vma->head) && !anonvma_external_refcount(anon_vma);
         spin_unlock(&anon_vma->lock);
 
         if (empty)
@@ -275,8 +274,7 @@ static void anon_vma_ctor(void *data)
         struct anon_vma *anon_vma = data;
 
         spin_lock_init(&anon_vma->lock);
-        ksm_refcount_init(anon_vma);
-        migrate_refcount_init(anon_vma);
+        anonvma_external_refcount_init(anon_vma);
         INIT_LIST_HEAD(&anon_vma->head);
 }