mm: memcontrol: remove obsolete kmemcg pinning tricks

As charges now pin the css explicitely, there is no more need for kmemcg
to acquire a proxy reference for outstanding pages during offlining, or
maintain state to identify such "dead" groups.

This was the last user of the uncharge functions' return values, so remove
them as well.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h
index 7cce3be..9554215 100644
--- a/include/linux/page_counter.h
+++ b/include/linux/page_counter.h
@@ -34,12 +34,12 @@
 	return atomic_long_read(&counter->count);
 }
 
-int page_counter_cancel(struct page_counter *counter, unsigned long nr_pages);
+void page_counter_cancel(struct page_counter *counter, unsigned long nr_pages);
 void page_counter_charge(struct page_counter *counter, unsigned long nr_pages);
 int page_counter_try_charge(struct page_counter *counter,
 			    unsigned long nr_pages,
 			    struct page_counter **fail);
-int page_counter_uncharge(struct page_counter *counter, unsigned long nr_pages);
+void page_counter_uncharge(struct page_counter *counter, unsigned long nr_pages);
 int page_counter_limit(struct page_counter *counter, unsigned long limit);
 int page_counter_memparse(const char *buf, unsigned long *nr_pages);