From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751843Ab2JOJEt (ORCPT ); Mon, 15 Oct 2012 05:04:49 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:37013 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751605Ab2JOJEs (ORCPT ); Mon, 15 Oct 2012 05:04:48 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v1.8.4 Message-ID: <507BD1A3.3040004@jp.fujitsu.com> Date: Mon, 15 Oct 2012 18:04:35 +0900 From: Kamezawa Hiroyuki User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:15.0) Gecko/20120907 Thunderbird/15.0.1 MIME-Version: 1.0 To: Michal Hocko CC: linux-mm@kvack.org, Dave Hansen , KOSAKI Motohiro , Andrew Morton , LKML Subject: Re: [PATCH] add some drop_caches documentation and info messsge References: <20121012125708.GJ10110@dhcp22.suse.cz> In-Reply-To: <20121012125708.GJ10110@dhcp22.suse.cz> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2012/10/12 21:57), Michal Hocko wrote: > Hi, > I would like to resurrect the following Dave's patch. The last time it > has been posted was here https://lkml.org/lkml/2010/9/16/250 and there > didn't seem to be any strong opposition. > Kosaki was worried about possible excessive logging when somebody drops > caches too often (but then he claimed he didn't have a strong opinion > on that) but I would say opposite. If somebody does that then I would > really like to know that from the log when supporting a system because > it almost for sure means that there is something fishy going on. It is > also worth mentioning that only root can write drop caches so this is > not an flooding attack vector. > I am bringing that up again because this can be really helpful when > chasing strange performance issues which (surprise surprise) turn out to > be related to artificially dropped caches done because the admin thinks > this would help... > > I have just refreshed the original patch on top of the current mm tree > but I could live with KERN_INFO as well if people think that KERN_NOTICE > is too hysterical. > --- > From 1f4058be9b089bc9d43d71bc63989335d7637d8d Mon Sep 17 00:00:00 2001 > From: Dave Hansen > Date: Fri, 12 Oct 2012 14:30:54 +0200 > Subject: [PATCH] add some drop_caches documentation and info messsge > > There is plenty of anecdotal evidence and a load of blog posts > suggesting that using "drop_caches" periodically keeps your system > running in "tip top shape". Perhaps adding some kernel > documentation will increase the amount of accurate data on its use. > > If we are not shrinking caches effectively, then we have real bugs. > Using drop_caches will simply mask the bugs and make them harder > to find, but certainly does not fix them, nor is it an appropriate > "workaround" to limit the size of the caches. > > It's a great debugging tool, and is really handy for doing things > like repeatable benchmark runs. So, add a bit more documentation > about it, and add a little KERN_NOTICE. It should help developers > who are chasing down reclaim-related bugs. > > [mhocko@suse.cz: refreshed to current -mm tree] > Signed-off-by: Dave Hansen > Reviewed-by: KAMEZAWA Hiroyuki > Acked-by: Michal Hocko Acked-by: KAMEZAWA Hiroyuki