mm: introduce "clear_freelist" kernel parameter

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4XB9H
CVE: NA

--------------------------------

CONFIG_CLEAR_FREELIST_PAGE specifies the default value for clear
freelist. Add a kernel parameter to make it possible to
override the default. Keep clear_freelist disabled unless
"clear_freelist" is explicitly specified.
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NLaibin Qiu <qiulaibin@huawei.com>

Documentation/admin-guide/kernel-parameters.txt

@@ -516,6 +516,10 @@
 
 	cio_ignore=	[S390]
 			See Documentation/s390/CommonIO for details.
+
+	clear_freelist
+			Enable clear_freelist feature.
+
 	clk_ignore_unused
 			[CLK]
 			Prevents the clock framework from automatically gating

mm/clear_freelist_page.c

@@ -154,9 +154,18 @@ static struct ctl_table sys_ctl_table[] = {
 	{ }
 };
 
+static bool clear_freelist_enabled;
+static int __init setup_clear_freelist(char *str)
+{
+	clear_freelist_enabled = true;
+	return 1;
+}
+__setup("clear_freelist", setup_clear_freelist);
+
 static int __init clear_freelist_init(void)
 {
-	register_sysctl_table(sys_ctl_table);
+	if (clear_freelist_enabled)
+		register_sysctl_table(sys_ctl_table);
 
 	return 0;
 }