linux-kernel - Re: [PATCH]vmscan: handle underflow for get_scan

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Date:	Thu, 15 Apr 2010 12:25:42 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	kosaki.motohiro@...fujitsu.com, Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Wu, Fengguang" <fengguang.wu@...el.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH]vmscan: handle underflow for get_scan_ratio

Hi

sorry for the delay.

> > After solving streaming io issue, I'll put it to mainline.
> if the streaming io issue is popular, how about below patch against my last one?
> we take priority == DEF_PRIORITY an exception.

Your patch seems works. but it is obviously ugly and bandaid patch.
So, I like single your previous patch rather than combinate this one.
Even though both dropping makes sense rather than both merge.

Please consider attack root cause.



> Index: linux/mm/vmscan.c
> ===================================================================
> --- linux.orig/mm/vmscan.c	2010-04-14 09:03:28.000000000 +0800
> +++ linux/mm/vmscan.c	2010-04-14 09:19:56.000000000 +0800
> @@ -1629,6 +1629,22 @@ static void get_scan_count(struct zone *
>  	fraction[0] = ap;
>  	fraction[1] = fp;
>  	denominator = ap + fp + 1;
> +
> +	/*
> +	 * memory pressure isn't high, we allow percentage underflow. This
> +	 * avoids swap in stream io case.
> +	 */
> +	if (priority == DEF_PRIORITY) {
> +		if (fraction[0] * 99 < fraction[1]) {
> +			fraction[0] = 0;
> +			fraction[1] = 1;
> +			denominator = 1;
> +		} else if (fraction[1] * 99 < fraction[0]) {
> +			fraction[0] = 1;
> +			fraction[1] = 0;
> +			denominator = 1;
> +		}
> +	}
>  out:
>  	for_each_evictable_lru(l) {
>  		int file = is_file_lru(l);
> 
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