Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765052AbXHKXOr (ORCPT ); Sat, 11 Aug 2007 19:14:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759108AbXHKXOi (ORCPT ); Sat, 11 Aug 2007 19:14:38 -0400 Received: from mailhost.nmt.edu ([129.138.4.52]:52190 "EHLO mailhost.nmt.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756740AbXHKXOh (ORCPT ); Sat, 11 Aug 2007 19:14:37 -0400 Date: Sat, 11 Aug 2007 17:14:28 -0600 From: Valerie Henson To: Martin Bligh Cc: Andrew Morton , Christoph Hellwig , J??rn Engel , Ingo Molnar , Jeff Garzik , Linus Torvalds , Peter Zijlstra , linux-mm@kvack.org, Linux Kernel Mailing List , miklos@szeredi.hu, neilb@suse.de, dgc@sgi.com, tomoki.sekiyama.qu@hitachi.com, nikita@clusterfs.com, trond.myklebust@fys.uio.no, yingchao.zhou@gmail.com, richard@rsk.demon.co.uk, david@lang.hm Subject: Re: [PATCH 00/23] per device dirty throttling -v8 Message-ID: <20070811231428.GA16355@rainbow> References: <46B4C0A8.1000902@garzik.org> <20070804191205.GA24723@lazybastard.org> <20070804192130.GA25346@elte.hu> <20070804192615.GA25600@lazybastard.org> <20070804194259.GA25753@lazybastard.org> <20070805203602.GB25107@infradead.org> <46BA3137.3020701@mbligh.org> <20070808142146.c85ab8d7.akpm@linux-foundation.org> <46BA65E1.8010704@mbligh.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <46BA65E1.8010704@mbligh.org> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1615 Lines: 36 On Wed, Aug 08, 2007 at 05:54:57PM -0700, Martin Bligh wrote: > Andrew Morton wrote: > >On Wed, 08 Aug 2007 14:10:15 -0700 > >"Martin J. Bligh" wrote: > > > >>Why isn't this easily fixable by just adding an additional dirty > >>flag that says atime has changed? Then we only cause a write > >>when we remove the inode from the inode cache, if only atime > >>is updated. > > > >I think that could be made to work, and it would fix the performance > >issue. > > > >It is a behaviour change. At present ext3 (for example) commits everything > >every five seconds. After a change like this, a crash+recovery could cause > >a file's atime to go backwards by an arbitrarily large time interval - it > >could easily be months. > > A second pdflush / workqueue at a slower rate would alleviate that. This becomes delayed atime writes. I'm not sure that it's better to batch up the writes and do them all in one big seeky go, or to trickle them out as they are done. Best of all is not to do them at all. Note when talking about saving up atime updates to write out that the final write is going to be sloooooow. Inodes are typically 128 bytes, and you may have to do a seek between every one. Currents disks can do on the order of 100 seeks a second. So do a find on 1000 files and you've just created 10 seconds of I/O hanging out in memory. -VAL - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/