linux-kernel - Re: Free memory never fully used, swapping

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Message-Id: <20101126195118.B6E7.A69D9226@jp.fujitsu.com>
Date:	Fri, 26 Nov 2010 20:03:04 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	kosaki.motohiro@...fujitsu.com, Simon Kirby <sim@...tway.ca>,
	Shaohua Li <shaohua.li@...el.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>
Subject: Re: Free memory never fully used, swapping

Two points.

> @@ -2310,10 +2324,12 @@ loop_again:
>  				 * spectulatively avoid congestion waits
>  				 */
>  				zone_clear_flag(zone, ZONE_CONGESTED);
> +				if (i <= pgdat->high_zoneidx)
> +					any_zone_ok = 1;
>  			}
>  
>  		}
> -		if (all_zones_ok)
> +		if (all_zones_ok || (order && any_zone_ok))
>  			break;		/* kswapd: all done */
>  		/*
>  		 * OK, kswapd is getting into trouble.  Take a nap, then take
> @@ -2336,7 +2352,7 @@ loop_again:
>  			break;
>  	}
>  out:
> -	if (!all_zones_ok) {
> +	if (!(all_zones_ok || (order && any_zone_ok))) {

This doesn't work ;)
kswapd have to clear ZONE_CONGESTED flag before enter sleeping.
otherwise nobody can clear it.

Say, we have to fill below condition.
 - All zone are successing zone_watermark_ok(order-0)
 - At least one zone are successing zone_watermark_ok(high-order)



> @@ -2417,6 +2439,7 @@ static int kswapd(void *p)
>  		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
>  		new_order = pgdat->kswapd_max_order;
>  		pgdat->kswapd_max_order = 0;
> +		pgdat->high_zoneidx = MAX_ORDER;

I don't think MAX_ORDER is correct ;)

        high_zoneidx = pgdat->high_zoneidx;
        pgdat->high_zoneidx = pgdat->nr_zones - 1;

?


And, we have another kswapd_max_order reading place. (after kswapd_try_to_sleep)
We need it too.




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