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From:   mateusznosek0@gmail.com
To:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc:     Mateusz Nosek <mateusznosek0@gmail.com>, akpm@linux-foundation.org
Subject: [PATCH] mm/page_poison.c: replace bool variable with static key
Date:   Mon, 21 Sep 2020 17:29:31 +0200
Message-Id: <20200921152931.938-1-mateusznosek0@gmail.com>
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From: Mateusz Nosek <mateusznosek0@gmail.com>

Variable 'want_page_poisoning' is a switch deciding if page poisoning
should be enabled. This patch changes it to be static key.

Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
---
 mm/page_poison.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/mm/page_poison.c b/mm/page_poison.c
index 34b9181ee5d1..ae0482cded87 100644
--- a/mm/page_poison.c
+++ b/mm/page_poison.c
@@ -8,13 +8,23 @@
 #include <linux/ratelimit.h>
 #include <linux/kasan.h>
 
-static bool want_page_poisoning __read_mostly;
+static DEFINE_STATIC_KEY_FALSE_RO(want_page_poisoning);
 
 static int __init early_page_poison_param(char *buf)
 {
-	if (!buf)
-		return -EINVAL;
-	return strtobool(buf, &want_page_poisoning);
+	int ret;
+	bool tmp;
+
+	ret = strtobool(buf, &tmp);
+	if (ret)
+		return ret;
+
+	if (tmp)
+		static_branch_enable(&want_page_poisoning);
+	else
+		static_branch_disable(&want_page_poisoning);
+
+	return 0;
 }
 early_param("page_poison", early_page_poison_param);
 
@@ -31,7 +41,7 @@ bool page_poisoning_enabled(void)
 	 * Page poisoning is debug page alloc for some arches. If
 	 * either of those options are enabled, enable poisoning.
 	 */
-	return (want_page_poisoning ||
+	return (static_branch_unlikely(&want_page_poisoning) ||
 		(!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
 		debug_pagealloc_enabled()));
 }
-- 
2.20.1