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, 2 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e286e1603e4f..660dfc27d971 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1080,7 +1080,7 @@ unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
                 if (unlikely(!PageCgroupUsed(pc)))
                         continue;
 
-                page = pc->page;
+                page = lookup_cgroup_page(pc);
 
                 if (unlikely(!PageLRU(page)))
                         continue;
@@ -3344,7 +3344,7 @@ static int mem_cgroup_force_empty_list(struct mem_cgroup *mem,
                 }
                 spin_unlock_irqrestore(&zone->lru_lock, flags);
 
-                page = pc->page;
+                page = lookup_cgroup_page(pc);
 
                 ret = mem_cgroup_move_parent(page, pc, mem, GFP_KERNEL);
                 if (ret == -ENOMEM)