Re: [PATCH 1/6] mm, oom: do not loop over all tasks if there are no external tasks sharing mm

Michal Hocko wrote:

+bool task_has_external_users(struct task_struct *p)
+{
+	struct mm_struct *mm = NULL;
+	struct task_struct *t;
+	int active_threads = 0;
+	bool ret = true;	/* be pessimistic */
+
+	rcu_read_lock();
+	for_each_thread(p, t) {
+		task_lock(t);
+		if (likely(t->mm)) {
+			active_threads++;
+			if (!mm) {
+				mm = t->mm;
+				atomic_inc(&mm->mm_count);
+			}
+		}
+		task_unlock(t);
+	}
+	rcu_read_unlock();
+

I don't like this. We might sleep here long enough to change mm_users.

+	if (mm) {
+		if (atomic_read(&mm->mm_users) <= active_threads)
+			ret = false;
+		mmdrop(mm);
+	}
+	return ret;
+}

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>