linux-kernel - [PATCH] CPU hotplug, writeback: Don't call writeback_set

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Date:	Tue, 25 Sep 2012 02:18:20 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Borislav Petkov <bp@...64.org>
CC:	Conny Seidel <conny.seidel@....com>, Jan Kara <jack@...e.cz>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Fengguang Wu <fengguang.wu@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <jweiner@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] CPU hotplug, writeback: Don't call writeback_set_ratelimit()
 too often during hotplug


From: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

The CPU hotplug callback related to writeback calls writeback_set_ratelimit()
during every state change in the hotplug sequence. This is unnecessary
since num_online_cpus() changes only once during the entire hotplug operation.

So invoke the function only once per hotplug, thereby avoiding the
unnecessary repetition of those costly calculations.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
---

 mm/page-writeback.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 5ad5ce2..830893b 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1602,10 +1602,18 @@ void writeback_set_ratelimit(void)
 }
 
 static int __cpuinit
-ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
+ratelimit_handler(struct notifier_block *self, unsigned long action,
+		  void *hcpu)
 {
-	writeback_set_ratelimit();
-	return NOTIFY_DONE;
+
+	switch (action & ~CPU_TASKS_FROZEN) {
+	case CPU_ONLINE:
+	case CPU_DEAD:
+		writeback_set_ratelimit();
+		return NOTIFY_OK;
+	default:
+		return NOTIFY_DONE;
+	}
 }
 
 static struct notifier_block __cpuinitdata ratelimit_nb = {


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