mm: memcontrol: remove unnecessary PCG_USED pc->mem_cgroup valid flag

pc->mem_cgroup had to be left intact after uncharge for the final LRU
removal, and !PCG_USED indicated whether the page was uncharged.  But
since commit 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API") pages
are uncharged after the final LRU removal.  Uncharge can simply clear
the pointer and the PCG_USED/PageCgroupUsed sites can test that instead.

Because this is the last page_cgroup flag, this patch reduces the memcg
per-page overhead to a single pointer.

[akpm@linux-foundation.org: remove unneeded initialization of `memcg', per Michal]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 10 deletions

diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index 97536e685843..1289be6b436c 100644
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h
@@ -1,11 +1,6 @@
 #ifndef __LINUX_PAGE_CGROUP_H
 #define __LINUX_PAGE_CGROUP_H
 
-enum {
-        /* flags for mem_cgroup */
-        PCG_USED = 0x01,        /* This page is charged to a memcg */
-};
-
 struct pglist_data;
 
 #ifdef CONFIG_MEMCG
@@ -19,7 +14,6 @@ struct mem_cgroup;
  * then the page cgroup for pfn always exists.
  */
 struct page_cgroup {
-        unsigned long flags;
         struct mem_cgroup *mem_cgroup;
 };
 
@@ -39,10 +33,6 @@ static inline void page_cgroup_init(void)
 
 struct page_cgroup *lookup_page_cgroup(struct page *page);
 
-static inline int PageCgroupUsed(struct page_cgroup *pc)
-{
-        return !!(pc->flags & PCG_USED);
-}
 #else /* !CONFIG_MEMCG */
 struct page_cgroup;