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 o4RE2ijM137846 for ; Thu, 27 May 2010 09:02:44 -0500 Received: from kaylee.flamingspork.com (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id EE70437BE01 for ; Thu, 27 May 2010 07:05:07 -0700 (PDT) Received: from kaylee.flamingspork.com (kaylee.flamingspork.com [74.207.245.61]) by cuda.sgi.com with ESMTP id haLaXHFKo2JunpKE for ; Thu, 27 May 2010 07:05:07 -0700 (PDT) From: Stewart Smith Subject: Re: NOW: o_direct -- WAS: Re: WARNING in xfs_lwr.c, xfs_write() In-Reply-To: <4BFD3926.6040208@hardwarefreak.com> References: <20100523002023.41f5a5c8@aaa.pulp.binarylife.net> <20100523101856.GL2150@dastard> <20100523092344.0fcaab42@aaa.pulp.binarylife.net> <4BF9FCA8.8090906@hardwarefreak.com> <20100524143428.6f3a117c@abend.internal.xtremedata.com> <20100526070620.GT2150@dastard> <4BFD3926.6040208@hardwarefreak.com> Date: Fri, 28 May 2010 00:05:05 +1000 Message-ID: <87mxvlbfu6.fsf@willster.local.flamingspork.com> MIME-Version: 1.0 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: Stan Hoeppner , xfs@oss.sgi.com On Wed, 26 May 2010 10:07:18 -0500, Stan Hoeppner wrote: > Please educate the ignorant a little bit Dave. I'm not a programmer, or at > least, haven't been one for a couple of decades. If o_direct is superior to > mmap, why then don't, say, Postfix and Dovecot use it instead of mmap? Email > servers are some of the most disk I/O bound applications on the planet. I > would think on heavily loaded mail servers (smtp or imap), at $big_isp for > example, buffer cache would yield very little performance gain, and may even > slow the system down due to buffer cache thrashing. email servers are metadata heavy workloads, not data heavy. They do lots of create/rename/delete of small files. O_DIRECT requires you to do IO in multiples of 512bytes aligned to 512byte boundaries. things like email servers... generally don't need/do that. Database servers tend to do that, so they use O_DIRECT. Also, email smtpd delivering a message on a machine, you could quite likely have imapd come along and read that soon after, so using the cache makes sense. > Why do you think Wietse and Timo don't use o_direct instead of mmap? Timo is > working on a complex and aggressive totally asynchronous I/O subsystem for a > future Dovecot release in an effort to speed up I/O on loaded systems. Could > o_direct not be the solution? AFAIK, both Postfix and Dovecot support running > on just about every Unix like OS on the planet. Is o_direct not a portable > interface, limited to Linux only? Is o_direct a POSIX standard? not posix. but you can get the functionality out of linux through opening with O_DIRECT, solaris by doing o_direct(), and who cares about the rest :) -- Stewart Smith _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs