mm: move anon_vma ref out from under CONFIG_foo

We need the anon_vma refcount unconditionally to simplify the anon_vma
lifetime rules.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Hugh Dickins <hughd@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 10 insertions, 44 deletions

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index b9b23ddca63a..fd56111a52c1 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -27,18 +27,15 @@
 struct anon_vma {
         struct anon_vma *root;  /* Root of this anon_vma tree */
         spinlock_t lock;        /* Serialize access to vma list */
-#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
+         * The refcount is taken on 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
+        atomic_t refcount;
+
         /*
          * NOTE: the LSB of the head.next is set by
          * mm_take_all_locks() _after_ taking the above lock. So the
@@ -71,41 +68,12 @@ struct anon_vma_chain {
 };
 
 #ifdef CONFIG_MMU
-#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
-static inline void anonvma_external_refcount_init(struct anon_vma *anon_vma)
-{
-        atomic_set(&anon_vma->external_refcount, 0);
-}
-
-static inline int anonvma_external_refcount(struct anon_vma *anon_vma)
-{
-        return atomic_read(&anon_vma->external_refcount);
-}
-
 static inline void get_anon_vma(struct anon_vma *anon_vma)
 {
-        atomic_inc(&anon_vma->external_refcount);
+        atomic_inc(&anon_vma->refcount);
 }
 
 void put_anon_vma(struct anon_vma *);
-#else
-static inline void anonvma_external_refcount_init(struct anon_vma *anon_vma)
-{
-}
-
-static inline int anonvma_external_refcount(struct anon_vma *anon_vma)
-{
-        return 0;
-}
-
-static inline void get_anon_vma(struct anon_vma *anon_vma)
-{
-}
-
-static inline void put_anon_vma(struct anon_vma *anon_vma)
-{
-}
-#endif /* CONFIG_KSM */
 
 static inline struct anon_vma *page_anon_vma(struct page *page)
 {
diff --git a/mm/rmap.c b/mm/rmap.c
index ad416afb2061..873cd9ef912c 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -272,7 +272,7 @@ 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) && !anonvma_external_refcount(anon_vma);
+        empty = list_empty(&anon_vma->head) && !atomic_read(&anon_vma->refcount);
         anon_vma_unlock(anon_vma);
 
         if (empty) {
@@ -303,7 +303,7 @@ static void anon_vma_ctor(void *data)
         struct anon_vma *anon_vma = data;
 
         spin_lock_init(&anon_vma->lock);
-        anonvma_external_refcount_init(anon_vma);
+        atomic_set(&anon_vma->refcount, 0);
         INIT_LIST_HEAD(&anon_vma->head);
 }
 
@@ -1486,7 +1486,6 @@ int try_to_munlock(struct page *page)
                 return try_to_unmap_file(page, TTU_MUNLOCK);
 }
 
-#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
 /*
  * Drop an anon_vma refcount, freeing the anon_vma and anon_vma->root
  * if necessary.  Be careful to do all the tests under the lock.  Once
@@ -1495,8 +1494,8 @@ int try_to_munlock(struct page *page)
  */
 void put_anon_vma(struct anon_vma *anon_vma)
 {
-        BUG_ON(atomic_read(&anon_vma->external_refcount) <= 0);
-        if (atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->root->lock)) {
+        BUG_ON(atomic_read(&anon_vma->refcount) <= 0);
+        if (atomic_dec_and_lock(&anon_vma->refcount, &anon_vma->root->lock)) {
                 struct anon_vma *root = anon_vma->root;
                 int empty = list_empty(&anon_vma->head);
                 int last_root_user = 0;
@@ -1507,8 +1506,8 @@ void put_anon_vma(struct anon_vma *anon_vma)
                  * the refcount on the root and check if we need to free it.
                  */
                 if (empty && anon_vma != root) {
-                        BUG_ON(atomic_read(&root->external_refcount) <= 0);
-                        last_root_user = atomic_dec_and_test(&root->external_refcount);
+                        BUG_ON(atomic_read(&root->refcount) <= 0);
+                        last_root_user = atomic_dec_and_test(&root->refcount);
                         root_empty = list_empty(&root->head);
                 }
                 anon_vma_unlock(anon_vma);
@@ -1520,7 +1519,6 @@ void put_anon_vma(struct anon_vma *anon_vma)
                 }
         }
 }
-#endif
 
 #ifdef CONFIG_MIGRATION
 /*