memcg: fix memory migration of shmem swapcache

In the current implementation mem_cgroup_end_migration() decides whether
the page migration has succeeded or not by checking "oldpage->mapping".

But if we are tring to migrate a shmem swapcache, the page->mapping of it
is NULL from the begining, so the check would be invalid.  As a result,
mem_cgroup_end_migration() assumes the migration has succeeded even if
it's not, so "newpage" would be freed while it's not uncharged.

This patch fixes it by passing mem_cgroup_end_migration() the result of
the page migration.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 067115c..6a576f9 100644 (file)
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -98,7 +98,7 @@ extern int
 mem_cgroup_prepare_migration(struct page *page,
        struct page *newpage, struct mem_cgroup **ptr);
 extern void mem_cgroup_end_migration(struct mem_cgroup *mem,
-       struct page *oldpage, struct page *newpage);
+       struct page *oldpage, struct page *newpage, bool migration_ok);
 
 /*
  * For memory reclaim.
@@ -251,8 +251,7 @@ mem_cgroup_prepare_migration(struct page *page, struct page *newpage,
 }
 
 static inline void mem_cgroup_end_migration(struct mem_cgroup *mem,
-                                       struct page *oldpage,
-                                       struct page *newpage)
+               struct page *oldpage, struct page *newpage, bool migration_ok)
 {
 }
 

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6424ba0..8ab8410 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2896,7 +2896,7 @@ int mem_cgroup_prepare_migration(struct page *page,
 
 /* remove redundant charge if migration failed*/
 void mem_cgroup_end_migration(struct mem_cgroup *mem,
-       struct page *oldpage, struct page *newpage)
+       struct page *oldpage, struct page *newpage, bool migration_ok)
 {
        struct page *used, *unused;
        struct page_cgroup *pc;
@@ -2905,8 +2905,7 @@ void mem_cgroup_end_migration(struct mem_cgroup *mem,
                return;
        /* blocks rmdir() */
        cgroup_exclude_rmdir(&mem->css);
-       /* at migration success, oldpage->mapping is NULL. */
-       if (oldpage->mapping) {
+       if (!migration_ok) {
                used = oldpage;
                unused = newpage;
        } else {

diff --git a/mm/migrate.c b/mm/migrate.c
index 5b7d1fd..46fe8cc 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -768,7 +768,7 @@ skip_unmap:
 
 uncharge:
        if (!charge)
-               mem_cgroup_end_migration(mem, page, newpage);
+               mem_cgroup_end_migration(mem, page, newpage, rc == 0);
 unlock:
        unlock_page(page);