From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx181.postini.com [74.125.245.181]) by kanga.kvack.org (Postfix) with SMTP id F11206B0075 for ; Thu, 25 Oct 2012 10:25:08 -0400 (EDT) Date: Thu, 25 Oct 2012 16:25:06 +0200 From: Michal Hocko Subject: Re: [PATCH] add some drop_caches documentation and info messsge Message-ID: <20121025142506.GH11105@dhcp22.suse.cz> References: <20121024125439.c17a510e.akpm@linux-foundation.org> <50884F63.8030606@linux.vnet.ibm.com> <20121024134836.a28d223a.akpm@linux-foundation.org> <20121024210600.GA17037@liondog.tnic> <50885B2E.5050500@linux.vnet.ibm.com> <20121024224817.GB8828@liondog.tnic> <5088725B.2090700@linux.vnet.ibm.com> <20121025092424.GA16601@liondog.tnic> <50892917.30201@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50892917.30201@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: Borislav Petkov , KOSAKI Motohiro , Andrew Morton , linux-mm@kvack.org, KAMEZAWA Hiroyuki , LKML On Thu 25-10-12 04:57:11, Dave Hansen wrote: [...] > Here's the problem: Joe Kernel Developer gets a bug report, usually > something like "the kernel is slow", or "the kernel is eating up all my > memory". We then start going and digging in to the problem with the > usual tools. We almost *ALWAYS* get dmesg, and it's reasonably common, > but less likely, that we get things like vmstat along with such a bug > report. > > Joe Kernel Developer digs in the statistics or the dmesg and tries to > figure out what happened. I've run in to a couple of cases in practice > (and I assume Michal has too) where the bug reporter was using > drop_caches _heavily_ and did not realize the implications. It was > quite hard to track down exactly how the page cache and dentries/inodes > were getting purged. Yes, very same here. Not that I would meet issues like that often but it happened in the past few times and it was always a lot of burnt time. > There are rarely oopses involved in these scenarios. > > The primary goal of this patch is to make debugging those scenarios > easier so that we can quickly realize that drop_caches is the reason our > caches went away, not some anomalous VM activity. A secondary goal is > to tell the user: "Hey, maybe this isn't something you want to be doing > all the time." -- Michal Hocko SUSE Labs -- 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