mm/page_owner: print memcg information

It was found that a number of offline memcgs were not freed because they
were pinned by some charged pages that were present.  Even "echo 1 >
/proc/sys/vm/drop_caches" wasn't able to free those pages.  These
offline but not freed memcgs tend to increase in number over time with
the side effect that percpu memory consumption as shown in /proc/meminfo
also increases over time.

In order to find out more information about those pages that pin offline
memcgs, the page_owner feature is extended to print memory cgroup
information especially whether the cgroup is offline or not.  RCU read
lock is taken when memcg is being accessed to make sure that it won't be
freed.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Waiman Long <[email protected]>
Acked-by: David Rientjes <[email protected]>
Acked-by: Roman Gushchin <[email protected]>
Acked-by: Rafael Aquini <[email protected]>
Acked-by: Mike Rapoport <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Ira Weiny <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Petr Mladek <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Steven Rostedt (Google) <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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