[PATCH 4/4] mm/swap: Enable "use_pvec_lock" nohz_full dependent

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

From: Anna-Maria Gleixner <anna-maria@linutronix.de>

When a system runs with CONFIG_NO_HZ_FULL enabled, the tick of CPUs listed
in 'nohz_full=' kernel command line parameter should be stopped whenever
possible. The tick stays longer stopped, when work for this CPU is handled
by another CPU.

With the already introduced static key 'use_pvec_lock' there is the
possibility to prevent firing a worker for mm/swap work on a remote CPU
with a stopped tick.

Therefore enabling the static key in case kernel command line parameter
'nohz_full=' setup was successful, which implies that CONFIG_NO_HZ_FULL is
set.

Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/sched/isolation.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index b02d148e76727..b532f448cab42 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -7,6 +7,7 @@
  *
  */
 #include "sched.h"
+#include "../../mm/internal.h"
 
 DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
 EXPORT_SYMBOL_GPL(housekeeping_overridden);
@@ -116,10 +117,21 @@ static int __init housekeeping_setup(char *str, enum hk_flags flags)
 static int __init housekeeping_nohz_full_setup(char *str)
 {
 	unsigned int flags;
+	int ret;
 
 	flags = HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | HK_FLAG_RCU | HK_FLAG_MISC;
 
-	return housekeeping_setup(str, flags);
+	ret = housekeeping_setup(str, flags);
+
+	/*
+	 * Protect struct pagevec with a lock instead using preemption disable;
+	 * with lock protection, remote handling of events instead of queue
+	 * work on remote cpu is default behavior.
+	 */
+	if (ret)
+		static_branch_enable(&use_pvec_lock);
+
+	return ret;
 }
 __setup("nohz_full=", housekeeping_nohz_full_setup);
 
-- 
2.20.1