linux-kernel - Re: [PATCH 2/6] mm: kswapd: Keep kswapd awake for high-order allocations until a percentage of the node is balanced

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Date:	Mon, 13 Dec 2010 11:03:01 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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>
Subject: Re: [PATCH 2/6] mm: kswapd: Keep kswapd awake for high-order
 allocations until a percentage of the node is balanced

On Fri, 10 Dec 2010 15:46:21 +0000
Mel Gorman <mel@....ul.ie> wrote:

> When reclaiming for high-orders, kswapd is responsible for balancing a
> node but it should not reclaim excessively. It avoids excessive reclaim by
> considering if any zone in a node is balanced then the node is balanced. In
> the cases where there are imbalanced zone sizes (e.g. ZONE_DMA with both
> ZONE_DMA32 and ZONE_NORMAL), kswapd can go to sleep prematurely as just
> one small zone was balanced.
> 
> This alters the sleep logic of kswapd slightly. It counts the number of pages
> that make up the balanced zones. If the total number of balanced pages is
> more than a quarter of the zone, kswapd will go back to sleep. This should
> keep a node balanced without reclaiming an excessive number of pages.
> 
> Signed-off-by: Mel Gorman <mel@....ul.ie>
> Reviewed-by: Minchan Kim <minchan.kim@...il.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

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