From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 42C4B6B01EF for ; Thu, 1 Apr 2010 18:16:48 -0400 (EDT) Date: Thu, 1 Apr 2010 15:16:39 -0700 From: Andrew Morton Subject: Re: [PATCH]vmscan: handle underflow for get_scan_ratio Message-Id: <20100401151639.a030fb10.akpm@linux-foundation.org> In-Reply-To: <20100331145602.03A7.A69D9226@jp.fujitsu.com> References: <20100331142708.039E.A69D9226@jp.fujitsu.com> <20100331055108.GA21963@localhost> <20100331145602.03A7.A69D9226@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: Wu Fengguang , "Li, Shaohua" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" List-ID: On Wed, 31 Mar 2010 15:00:52 +0900 (JST) KOSAKI Motohiro wrote: > > KOSAKI-san, > > > > On Wed, Mar 31, 2010 at 01:38:12PM +0800, KOSAKI Motohiro wrote: > > > > On Tue, Mar 30, 2010 at 02:08:53PM +0800, KOSAKI Motohiro wrote: > > > > > 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. > > > > if 1% is still big, how about below patch? > > > > > > This patch makes a lot of sense than previous. however I think <1% anon ratio > > > shouldn't happen anyway because file lru doesn't have reclaimable pages. > > > <1% seems no good reclaim rate. > > > > > > perhaps I'll take your patch for stable tree. but we need to attack the root > > > cause. iow, I guess we need to fix scan ratio equation itself. > > > > I tend to regard this patch as a general improvement for both > > .33-stable and .34. > > > > I do agree with you that it's desirable to do more test&analyze and > > check further for possibly hidden problems. > > Yeah, I don't want ignore .33-stable too. if I can't find the root cause > in 2-3 days, I'll revert guilty patch anyway. > It's a good idea to avoid fixing a bug one-way-in-stable, other-way-in-mainline. Because then we have new code in both trees which is different. And the -stable guys sensibly like to see code get a bit of a shakedown in mainline before backporting it. So it would be better to merge the "simple" patch into mainline, tagged for -stable backporting. Then we can later implement the larger fix in mainline, perhaps starting by reverting the "simple" fix. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org