linux-kernel - [PATCH] kswapd: assign new_order and new_classzone

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Message-Id: <1311903908-18263-1-git-send-email-alex.shi@intel.com>
Date:	Fri, 29 Jul 2011 09:45:08 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	linux-mm@...ck.org, P@...igBrady.com
Cc:	mgorman@...e.de, minchan.kim@...il.com,
	linux-kernel@...r.kernel.org, andrea@...share.com,
	tim.c.chen@...el.com, shaohua.li@...el.com,
	akpm@...ux-foundation.org, riel@...hat.com, luto@....edu
Subject: [PATCH] kswapd: assign new_order and new_classzone_idx after wakeup in sleeping

There 2 place to read pgdat in kswapd. One is return from a successful
balance, another is waked up from sleeping. But the new_order and
new_classzone_idx are not assigned after kswapd_try_to_sleep(), that
will cause a bug in the following scenario.

After the last time successful balance, kswapd goes to sleep. So the
new_order and new_classzone_idx were assigned to 0 and MAX-1 since there
is no new wakeup during last time balancing. Now, a new wakeup came and
finish balancing successful with order > 0. But since new_order is still
0, this time successful balancing were judged as a failed balance. so,
if there is another new wakeup coming during balancing, kswapd cann't
read this and still want to try to sleep. And if the new wakeup is a
tighter request, kswapd may goes to sleep, not to do balancing. That is
incorrect.

So, to avoid above problem, the new_order and new_classzone_idx need to
be assigned for later successful comparison.

Paidrag Brady, Could like do a retry for your problem on this patch?

Signed-off-by: Alex Shi <alex.shi@...el.com>
Acked-by: Mel Gorman <mgorman@...e.de>
---
 mm/vmscan.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7ef6912..eb7bcce 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2850,6 +2850,8 @@ static int kswapd(void *p)
 			kswapd_try_to_sleep(pgdat, order, classzone_idx);
 			order = pgdat->kswapd_max_order;
 			classzone_idx = pgdat->classzone_idx;
+			new_order = order;
+			new_classzone_idx = classzone_idx;
 			pgdat->kswapd_max_order = 0;
 			pgdat->classzone_idx = pgdat->nr_zones - 1;
 		}
-- 
1.6.3.3

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