From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda2.sgi.com [192.48.176.25]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id q8K650uJ040398 for ; Thu, 20 Sep 2012 01:05:01 -0500 Received: from ipmail04.adl6.internode.on.net (ipmail04.adl6.internode.on.net [150.101.137.141]) by cuda.sgi.com with ESMTP id V0PYKRS8aTlIAcP6 for ; Wed, 19 Sep 2012 23:06:11 -0700 (PDT) Date: Thu, 20 Sep 2012 16:05:43 +1000 From: Dave Chinner Subject: Re: Writeback Stalls Message-ID: <20120920060543.GH31501@dastard> References: <12EF8D94C6F8734FB2FF37B9FBEDD1735831B7A3@EXCHANGE.collogia.de> <20120919213427.GD31501@dastard> <12EF8D94C6F8734FB2FF37B9FBEDD1735831B7C9@EXCHANGE.collogia.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <12EF8D94C6F8734FB2FF37B9FBEDD1735831B7C9@EXCHANGE.collogia.de> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Markus Stockhausen Cc: "xfs@oss.sgi.com" On Thu, Sep 20, 2012 at 04:33:09AM +0000, Markus Stockhausen wrote: > > Fundamentally, you are doing it all wrong. High throughput, low > > latency NFS servers write dirty data to disk fast, not leave it > > memory until you run out of clean memory because that causes > > everything to block waiting for writeback IO completion to be ale to > > free memory... > > Maybe I did not make it clear enough. Plenty clear enough. Maybe I did not make it clear enough: Nobody has the time to try to diagnose a problem on a configuration that is obviously broken and pessimal for writeback behaviour. The first step is to report your actual problem, not an artificial behaviour you *think* demonstrates the same problem.... > The above setup is only > for demonstration purposes. To expose the problem better. In > real life we can see stalls tat thange from 0.5-1 seconds. Even > with all caches active, small dirty writeback settings and unlimited > bandwidth. So describe the application, etc that you see this problem. Start with: http://xfs.org/index.php/XFS_FAQ#Q:_What_information_should_I_include_when_reporting_a_problem.3F and we can go from there. > In between I found others complaining about the same problem: > > http://lwn.net/Articles/486313/ > http://oss.sgi.com/archives/xfs/2011-09/msg00189.html How do you know they are the same problem? Indeed, they aren't even writeback problems - they are application IO latency issues caused by the introduction of stable pages during writeback. > So just one last question: Can I savely revert the the mentioned > commit d76ee18a8551e33ad7dbd55cac38bc7b094f3abb if I only > write data to a battery backed up hardware raid controller on a > server that is attached to an UPS? NFS servers don't use mmap, so that patch is not causing your writeback problems. Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs