linux-kernel - [PATCH 4/6] mm: kswapd: Reset kswapd_max_order and classzone

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Date:	Fri, 10 Dec 2010 15:46:23 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Simon Kirby <sim@...tway.ca>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Shaohua Li <shaohua.li@...el.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Mel Gorman <mel@....ul.ie>
Subject: [PATCH 4/6] mm: kswapd: Reset kswapd_max_order and classzone_idx after reading

When kswapd wakes up, it reads its order and classzone from pgdat and
calls balance_pgdat. While its awake, it potentially reclaimes at a high
order and a low classzone index. This might have been a once-off that
was not required by subsequent callers. However, because the pgdat
values were not reset, they remain artifically high while
balance_pgdat() is running and potentially kswapd enters a second
unnecessary reclaim cycle. Reset the pgdat order and classzone index
after reading.

Signed-off-by: Mel Gorman <mel@....ul.ie>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
 mm/vmscan.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4d968b0..e1be4e8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2646,6 +2646,8 @@ static int kswapd(void *p)
 			kswapd_try_to_sleep(pgdat, order);
 			order = pgdat->kswapd_max_order;
 			classzone_idx = pgdat->classzone_idx;
+			pgdat->kswapd_max_order = 0;
+			pgdat->classzone_idx = MAX_NR_ZONES - 1;
 		}
 
 		ret = try_to_freeze();
-- 
1.7.1

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