oom: make oom_unkillable_task() helper function

Presently we have the same task check in two places. Unify it.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Cc: David Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/oom_kill.c

@@ -101,6 +101,26 @@ static struct task_struct *find_lock_task_mm(struct task_struct *p)
 	return NULL;
 }
 
+/* return true if the task is not adequate as candidate victim task. */
+static bool oom_unkillable_task(struct task_struct *p, struct mem_cgroup *mem,
+			   const nodemask_t *nodemask)
+{
+	if (is_global_init(p))
+		return true;
+	if (p->flags & PF_KTHREAD)
+		return true;
+
+	/* When mem_cgroup_out_of_memory() and p is not member of the group */
+	if (mem && !task_in_mem_cgroup(p, mem))
+		return true;
+
+	/* p may not have freeable memory in nodemask */
+	if (!has_intersects_mems_allowed(p, nodemask))
+		return true;
+
+	return false;
+}
+
 /**
  * badness - calculate a numeric value for how bad this task has been
  * @p: task struct of which task we should calculate
@@ -295,12 +315,7 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
 	for_each_process(p) {
 		unsigned long points;
 
-		/* skip the init task and kthreads */
-		if (is_global_init(p) || (p->flags & PF_KTHREAD))
-			continue;
-		if (mem && !task_in_mem_cgroup(p, mem))
-			continue;
-		if (!has_intersects_mems_allowed(p, nodemask))
+		if (oom_unkillable_task(p, mem, nodemask))
 			continue;
 
 		/*
@@ -467,11 +482,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 
 			if (child->mm == p->mm)
 				continue;
-			if (child->flags & PF_KTHREAD)
-				continue;
-			if (mem && !task_in_mem_cgroup(child, mem))
-				continue;
-			if (!has_intersects_mems_allowed(child, nodemask))
+			if (oom_unkillable_task(p, mem, nodemask))
 				continue;
 
 			/* badness() returns 0 if the thread is unkillable */