netdev - Re: [PATCH 1/5] page allocator: Always wake kswapd when restarting an allocation attempt after direct reclaim failed

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Message-ID: <alpine.DEB.2.00.0910260005500.15361@chino.kir.corp.google.com>
Date:	Mon, 26 Oct 2009 00:10:25 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	Mel Gorman <mel@....ul.ie>, Frans Pop <elendil@...net.nl>,
	Jiri Kosina <jkosina@...e.cz>,
	Sven Geggus <lists@...hsschwanzdomain.de>,
	Karol Lewandowski <karol.k.lewandowski@...il.com>,
	Tobias Oetiker <tobi@...iker.ch>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	David Miller <davem@...emloft.net>,
	Reinette Chatre <reinette.chatre@...el.com>,
	Kalle Valo <kalle.valo@....fi>,
	Mohamed Abbas <mohamed.abbas@...el.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	"John W. Linville" <linville@...driver.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Stephan von Krawczynski <skraw@...net.com>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	"linux-mm@...ck.org\"" <linux-mm@...ck.org>
Subject: Re: [PATCH 1/5] page allocator: Always wake kswapd when restarting
 an allocation attempt after direct reclaim failed

On Mon, 26 Oct 2009, KOSAKI Motohiro wrote:

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index bf72055..5a27896 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1899,6 +1899,12 @@ rebalance:
>  	if (should_alloc_retry(gfp_mask, order, pages_reclaimed)) {
>  		/* Wait for some write requests to complete then retry */
>  		congestion_wait(BLK_RW_ASYNC, HZ/50);
> +
> +		/*
> +		 * While we wait congestion wait, Amount of free memory can
> +		 * be changed dramatically. Thus, we kick kswapd again.
> +		 */
> +		wake_all_kswapd(order, zonelist, high_zoneidx);
>  		goto rebalance;
>  	}
>  

We're blocking to finish writeback of the directly reclaimed memory, why 
do we need to wake kswapd afterwards?
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