memcg: make page->mapping NULL before uncharge

This patch tries to make page->mapping to be NULL before
mem_cgroup_uncharge_cache_page() is called.

"page->mapping == NULL" is a good check for "whether the page is still
radix-tree or not".  This patch also adds BUG_ON() to
mem_cgroup_uncharge_cache_page();

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index 11c6c56ec017..6602941bfab0 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -330,8 +330,6 @@ static int migrate_page_move_mapping(struct address_space *mapping,
         __inc_zone_page_state(newpage, NR_FILE_PAGES);
 
         spin_unlock_irq(&mapping->tree_lock);
-        if (!PageSwapCache(newpage))
-                mem_cgroup_uncharge_cache_page(page);
 
         return 0;
 }
@@ -341,6 +339,8 @@ static int migrate_page_move_mapping(struct address_space *mapping,
  */
 static void migrate_page_copy(struct page *newpage, struct page *page)
 {
+        int anon;
+
         copy_highpage(newpage, page);
 
         if (PageError(page))
@@ -378,8 +378,13 @@ static void migrate_page_copy(struct page *newpage, struct page *page)
 #endif
         ClearPagePrivate(page);
         set_page_private(page, 0);
+        /* page->mapping contains a flag for PageAnon() */
+        anon = PageAnon(page);
         page->mapping = NULL;
 
+        if (!anon) /* This page was removed from radix-tree. */
+                mem_cgroup_uncharge_cache_page(page);
+
         /*
          * If any waiters have accumulated on the new page then
          * wake them up.