memcg: update memcg_test.txt

Update memcg_test.txt to describe how to test the move-charge feature.
Signed-off-by: NDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: NBalbir Singh <balbir@linux.vnet.ibm.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/cgroups/memcg_test.txt

 Memory Resource Controller(Memcg)  Implementation Memo.
-Last Updated: 2009/1/20
-Base Kernel Version: based on 2.6.29-rc2.
+Last Updated: 2010/2
+Base Kernel Version: based on 2.6.33-rc7-mm(candidate for 34).
 
 Because VM is getting complex (one of reasons is memcg...), memcg's behavior
 is complex. This is a document for memcg's internal behavior.
@@ -378,3 +378,21 @@ Under below explanation, we assume CONFIG_MEM_RES_CTRL_SWAP=y.
 	#echo 50M > memory.limit_in_bytes
 	#echo 50M > memory.memsw.limit_in_bytes
 	run 51M of malloc
+
+ 9.9 Move charges at task migration
+	Charges associated with a task can be moved along with task migration.
+
+	(Shell-A)
+	#mkdir /cgroup/A
+	#echo $$ >/cgroup/A/tasks
+	run some programs which uses some amount of memory in /cgroup/A.
+
+	(Shell-B)
+	#mkdir /cgroup/B
+	#echo 1 >/cgroup/B/memory.move_charge_at_immigrate
+	#echo "pid of the program running in group A" >/cgroup/B/tasks
+
+	You can see charges have been moved by reading *.usage_in_bytes or
+	memory.stat of both A and B.
+	See 8.2 of Documentation/cgroups/memory.txt to see what value should be
+	written to move_charge_at_immigrate.