linux-kernel - [PATCH 3.2 139/221] writeback: add missing INITIAL_JIFFIES init in global_update

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Date:	Tue, 05 May 2015 02:16:39 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Jan Kara" <jack@...e.cz>,
	"Tejun Heo" <tj@...nel.org>, "Jens Axboe" <axboe@...com>,
	"Jens Axboe" <axboe@...nel.dk>,
	"Wu Fengguang" <fengguang.wu@...el.com>
Subject: [PATCH 3.2 139/221] writeback: add missing INITIAL_JIFFIES init
 in global_update_bandwidth()

3.2.69-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Tejun Heo <tj@...nel.org>

commit 7d70e15480c0450d2bfafaad338a32e884fc215e upstream.

global_update_bandwidth() uses static variable update_time as the
timestamp for the last update but forgets to initialize it to
INITIALIZE_JIFFIES.

This means that global_dirty_limit will be 5 mins into the future on
32bit and some large amount jiffies into the past on 64bit.  This
isn't critical as the only effect is that global_dirty_limit won't be
updated for the first 5 mins after booting on 32bit machines,
especially given the auxiliary nature of global_dirty_limit's role -
protecting against global dirty threshold's sudden dips; however, it
does lead to unintended suboptimal behavior.  Fix it.

Fixes: c42843f2f0bb ("writeback: introduce smoothed global dirty limit")
Signed-off-by: Tejun Heo <tj@...nel.org>
Acked-by: Jan Kara <jack@...e.cz>
Cc: Wu Fengguang <fengguang.wu@...el.com>
Cc: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Jens Axboe <axboe@...com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 mm/page-writeback.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -726,7 +726,7 @@ static void global_update_bandwidth(unsi
 				    unsigned long now)
 {
 	static DEFINE_SPINLOCK(dirty_lock);
-	static unsigned long update_time;
+	static unsigned long update_time = INITIAL_JIFFIES;

 	/*
 	 * check locklessly first to optimize away locking for the most time

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