From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx139.postini.com [74.125.245.139]) by kanga.kvack.org (Postfix) with SMTP id D08FE6B0044 for ; Fri, 12 Oct 2012 14:54:29 -0400 (EDT) Received: by mail-oa0-f41.google.com with SMTP id k14so3904646oag.14 for ; Fri, 12 Oct 2012 11:54:29 -0700 (PDT) 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 Message-ID: Subject: Re: [PATCH] add some drop_caches documentation and info messsge Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-mm@kvack.org, Dave Hansen , KAMEZAWA Hiroyuki , Andrew Morton , LKML 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, 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