linux-kernel - Re: [PATCH 5/6] mm: kswapd: Treat zone->all_unreclaimable in sleeping_prematurely similar to balance

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Date:	Fri, 10 Dec 2010 10:23:37 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
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>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] mm: kswapd: Treat zone->all_unreclaimable in
 sleeping_prematurely similar to balance_pgdat()

On Thu,  9 Dec 2010 11:18:19 +0000
Mel Gorman <mel@....ul.ie> wrote:

> After DEF_PRIORITY, balance_pgdat() considers all_unreclaimable zones to
> be balanced but sleeping_prematurely does not. This can force kswapd to
> stay awake longer than it should. This patch fixes it.
> 
> Signed-off-by: Mel Gorman <mel@....ul.ie>

Hmm, maybe the logic works well but I don't like very much.

How about adding below instead of pgdat->node_present_pages ?

static unsigned long required_balanced_pages(pgdat, classzone_idx)
{
	unsigned long present = 0;

	for_each_zone_in_node(zone, pgdat) {
		if (zone->all_unreclaimable) /* Ignore unreclaimable zone at checking balance */
			continue;
		if (zone_idx(zone) > classzone_idx)
			continue;
		present = zone->present_pages;
	}
	return present;
}

> ---
>  mm/vmscan.c |   10 +++++++++-
>  1 files changed, 9 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index bc233d8..d7b0a3c 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2149,8 +2149,16 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
>  		if (!populated_zone(zone))
>  			continue;
>  
> -		if (zone->all_unreclaimable)
> +		/*
> +		 * balance_pgdat() skips over all_unreclaimable after
> +		 * DEF_PRIORITY. Effectively, it considers them balanced so
> +		 * they must be considered balanced here as well if kswapd
> +		 * is to sleep
> +		 */
> +		if (zone->all_unreclaimable) {
> +			balanced += zone->present_pages;
>  			continue;
> +		}
>  
>  		if (!zone_watermark_ok(zone, order, high_wmark_pages(zone),
>  								0, 0))
> -- 
> 1.7.1
> 
> --
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