From: Christoph Hellwig Subject: Re: ext4 writepages is making tiny bios? Date: Tue, 1 Sep 2009 17:27:40 -0400 Message-ID: <20090901212740.GA9930@infradead.org> References: <20090901184450.GB7885@think> <20090901205744.GE6996@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Chris Mason , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org To: Theodore Tso Return-path: Received: from bombadil.infradead.org ([18.85.46.34]:35753 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752331AbZIAV1i (ORCPT ); Tue, 1 Sep 2009 17:27:38 -0400 Content-Disposition: inline In-Reply-To: <20090901205744.GE6996@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Sep 01, 2009 at 04:57:44PM -0400, Theodore Tso wrote: > > This graph shows the difference: > > > > http://oss.oracle.com/~mason/seekwatcher/trace-buffered.png > > Wow, I'm surprised how seeky XFS was in these graphs compared to ext4 > and btrfs. I wonder what was going on. XFS did the mistake of trusting the VM, while everyone more or less overrode it. Removing all those checks and writing out much larger data fixes it with a relatively small patch: http://verein.lst.de/~hch/xfs/xfs-writeback-scaling when that code was last benchamrked extensively (on SLES9) it worked nicely to saturate extremly large machines using buffered I/O, since then VM tuning basically destroyed it.