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

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Message-Id: <20100330150453.8E9F.A69D9226@jp.fujitsu.com>
Date:	Tue, 30 Mar 2010 15:08:53 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	kosaki.motohiro@...fujitsu.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	fengguang.wu@...el.com
Subject: Re: [PATCH]vmscan: handle underflow for get_scan_ratio

Hi

> Commit 84b18490d1f1bc7ed5095c929f78bc002eb70f26 introduces a regression.
> With it, our tmpfs test always oom. The test has a lot of rotated anon
> pages and cause percent[0] zero. Actually the percent[0] is a very small
> value, but our calculation round it to zero. The commit makes vmscan
> completely skip anon pages and cause oops.
> An option is if percent[x] is zero in get_scan_ratio(), forces it
> to 1. See below patch.
> But the offending commit still changes behavior. Without the commit, we scan
> all pages if priority is zero, below patch doesn't fix this. Don't know if
> It's required to fix this too.

Can you please post your /proc/meminfo and reproduce program? I'll digg it.

Very unfortunately, this patch isn't acceptable. In past time, vmscan 
had similar logic, but 1% swap-out made lots bug reports. 



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