Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754337Ab2JLSyb (ORCPT ); Fri, 12 Oct 2012 14:54:31 -0400 Received: from mail-oa0-f46.google.com ([209.85.219.46]:35940 "EHLO mail-oa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752248Ab2JLSy3 (ORCPT ); Fri, 12 Oct 2012 14:54:29 -0400 MIME-Version: 1.0 In-Reply-To: <20121012125708.GJ10110@dhcp22.suse.cz> References: <20121012125708.GJ10110@dhcp22.suse.cz> From: KOSAKI Motohiro Date: Fri, 12 Oct 2012 14:54:08 -0400 X-Google-Sender-Auth: wsUzi3o2pYRj7PrTxEO22zdfIgU Message-ID: Subject: Re: [PATCH] add some drop_caches documentation and info messsge To: Michal Hocko Cc: linux-mm@kvack.org, Dave Hansen , KAMEZAWA Hiroyuki , Andrew Morton , LKML Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2686 Lines: 54 On Fri, Oct 12, 2012 at 8:57 AM, 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 Looks fine. Acked-by: KOSAKI Motohiro -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/