Memory controller: task migration

Allow tasks to migrate from one cgroup to the other.  We migrate
mm_struct's mem_cgroup only when the thread group id migrates.

Signed-off-by: Balbir Singh <[email protected]>
Cc: Pavel Emelianov <[email protected]>
Cc: Paul Menage <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Kirill Korotaev <[email protected]>
Cc: Herbert Poetzl <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Vaidyanathan Srinivasan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/memcontrol.c

@@ -326,11 +326,46 @@ static int mem_cgroup_populate(struct cgroup_subsys *ss,
 					ARRAY_SIZE(mem_cgroup_files));
 }
 
+static void mem_cgroup_move_task(struct cgroup_subsys *ss,
+				struct cgroup *cont,
+				struct cgroup *old_cont,
+				struct task_struct *p)
+{
+	struct mm_struct *mm;
+	struct mem_cgroup *mem, *old_mem;
+
+	mm = get_task_mm(p);
+	if (mm == NULL)
+		return;
+
+	mem = mem_cgroup_from_cont(cont);
+	old_mem = mem_cgroup_from_cont(old_cont);
+
+	if (mem == old_mem)
+		goto out;
+
+	/*
+	 * Only thread group leaders are allowed to migrate, the mm_struct is
+	 * in effect owned by the leader
+	 */
+	if (p->tgid != p->pid)
+		goto out;
+
+	css_get(&mem->css);
+	rcu_assign_pointer(mm->mem_cgroup, mem);
+	css_put(&old_mem->css);
+
+out:
+	mmput(mm);
+	return;
+}
+
 struct cgroup_subsys mem_cgroup_subsys = {
 	.name = "memory",
 	.subsys_id = mem_cgroup_subsys_id,
 	.create = mem_cgroup_create,
 	.destroy = mem_cgroup_destroy,
 	.populate = mem_cgroup_populate,
+	.attach = mem_cgroup_move_task,
 	.early_init = 1,
 };