memcg: remove direct page_cgroup-to-page pointer

In struct page_cgroup, we have a full word for flags but only a few are
reserved.  Use the remaining upper bits to encode, depending on
configuration, the node or the section, to enable page_cgroup-to-page
lookups without a direct pointer.

This saves a full word for every page in a system with memory cgroups
enabled.

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

1 files changed, 2 insertions, 0 deletions

diff --git a/kernel/bounds.c b/kernel/bounds.c
index 98a51f26c136..0c9b862292b2 100644
--- a/kernel/bounds.c
+++ b/kernel/bounds.c
@@ -9,11 +9,13 @@
 #include <linux/page-flags.h>
 #include <linux/mmzone.h>
 #include <linux/kbuild.h>
+#include <linux/page_cgroup.h>
 
 void foo(void)
 {
         /* The enum constants to put into include/generated/bounds.h */
         DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
         DEFINE(MAX_NR_ZONES, __MAX_NR_ZONES);
+        DEFINE(NR_PCG_FLAGS, __NR_PCG_FLAGS);
         /* End of constants */
 }