memcg: update menuconfig help text

page_cgroup is now allocated at boot and memmap doesn't includes pointer
for page_cgroup.  Fix the menu help text.

Reviewed-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-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>

init/Kconfig

@@ -401,16 +401,20 @@ config CGROUP_MEM_RES_CTLR
 	depends on CGROUPS && RESOURCE_COUNTERS
 	select MM_OWNER
 	help
-	  Provides a memory resource controller that manages both page cache and
-	  RSS memory.
+	  Provides a memory resource controller that manages both anonymous
+	  memory and page cache. (See Documentation/controllers/memory.txt)
 
 	  Note that setting this option increases fixed memory overhead
-	  associated with each page of memory in the system by 4/8 bytes
-	  and also increases cache misses because struct page on many 64bit
-	  systems will not fit into a single cache line anymore.
+	  associated with each page of memory in the system. By this,
+	  20(40)bytes/PAGE_SIZE on 32(64)bit system will be occupied by memory
+	  usage tracking struct at boot. Total amount of this is printed out
+	  at boot.
 
 	  Only enable when you're ok with these trade offs and really
-	  sure you need the memory resource controller.
+	  sure you need the memory resource controller. Even when you enable
+	  this, you can set "cgroup_disable=memory" at your boot option to
+	  disable memory resource controller and you can avoid overheads.
+	  (and lose benefits of memory resource contoller)
 
 	  This config option also selects MM_OWNER config option, which
 	  could in turn add some fork/exit overhead.