linux-kernel - Re: [PATCH] vmscan: skip freeing memory from zones with lots free

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Date:	Fri, 28 Nov 2008 12:30:14 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] vmscan: skip freeing memory from zones with lots free

On Fri, 2008-11-28 at 06:08 -0500, Rik van Riel wrote:
> Skip freeing memory from zones that already have lots of free memory.
> If one memory zone has harder to free memory, we want to avoid freeing
> excessive amounts of memory from other zones, if only because pageout
> IO from the other zones can slow down page freeing from the problem zone.
> 
> This is similar to the check already done by kswapd in balance_pgdat().
> 
> Signed-off-by: Rik van Riel <riel@...hat.com>

Make sense,

Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

> ---
> Kosaki-san, this should address point (3) from your list.
> 
>  mm/vmscan.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> Index: linux-2.6.28-rc5/mm/vmscan.c
> ===================================================================
> --- linux-2.6.28-rc5.orig/mm/vmscan.c	2008-11-28 05:53:56.000000000 -0500
> +++ linux-2.6.28-rc5/mm/vmscan.c	2008-11-28 06:05:29.000000000 -0500
> @@ -1510,6 +1510,9 @@ static unsigned long shrink_zones(int pr
>  			if (zone_is_all_unreclaimable(zone) &&
>  						priority != DEF_PRIORITY)
>  				continue;	/* Let kswapd poll it */
> +			if (zone_watermark_ok(zone, sc->order,
> +					4*zone->pages_high, high_zoneidx, 0))
> +				continue;	/* Lots free already */
>  			sc->all_unreclaimable = 0;
>  		} else {
>  			/*
> 
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