Re: [PATCH 2/2 v3] mm/compaction: Disable compact_unevictable_allowed on RT

On 3/4/20 12:56 AM, Andrew Morton wrote:

quoted

@@ -2572,6 +2577,26 @@ int proc_dointvec(struct ctl_table *table, int write,
 	return do_proc_dointvec(table, write, buffer, lenp, ppos, NULL, NULL);
 }
 
+#ifdef CONFIG_COMPACTION
+static int proc_dointvec_warn_RT_change(struct ctl_table *table, int write,
+					void __user *buffer, size_t *lenp,
+					loff_t *ppos)
+{
+	int ret, old;
+
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || !write)
+		return proc_dointvec(table, write, buffer, lenp, ppos);
+
+	old = *(int *)table->data;
+	ret = proc_dointvec(table, write, buffer, lenp, ppos);
+	if (ret)
+		return ret;
+	WARN_ONCE(old != *(int *)table->data, "sysctl attribute %s changed.",
+		  table->procname);

The WARN will include a stack trace which just isn't interesting.  A
pr_warn() would be better?

Yeah, the only interesting part of full WARN would possibly be, which process
changed it. That might be useful to print.

quoted

+	return ret;
+}
+#endif