mm: migration: share the anon_vma ref counts between KSM and page migration

For clarity of review, KSM and page migration have separate refcounts on
the anon_vma.  While clear, this is a waste of memory.  This patch gets
KSM and page migration to share their toys in a spirit of harmony.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 6 insertions, 8 deletions

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);
 }