Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758608AbZCZOs1 (ORCPT ); Thu, 26 Mar 2009 10:48:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758293AbZCZOsN (ORCPT ); Thu, 26 Mar 2009 10:48:13 -0400 Received: from THUNK.ORG ([69.25.196.29]:36722 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758801AbZCZOsM (ORCPT ); Thu, 26 Mar 2009 10:48:12 -0400 Date: Thu, 26 Mar 2009 10:47:07 -0400 From: Theodore Tso To: Ingo Molnar Cc: Jan Kara , Linus Torvalds , Andrew Morton , Alan Cox , Arjan van de Ven , Peter Zijlstra , Nick Piggin , Jens Axboe , David Rees , Jesper Krogh , Linux Kernel Mailing List , Oleg Nesterov , Roland McGrath Subject: Re: ext3 IO latency measurements (was: Linux 2.6.29) Message-ID: <20090326144707.GA6239@mit.edu> Mail-Followup-To: Theodore Tso , Ingo Molnar , Jan Kara , Linus Torvalds , Andrew Morton , Alan Cox , Arjan van de Ven , Peter Zijlstra , Nick Piggin , Jens Axboe , David Rees , Jesper Krogh , Linux Kernel Mailing List , Oleg Nesterov , Roland McGrath References: <20090325150041.GM32307@mit.edu> <20090325185824.GO32307@mit.edu> <20090325215137.GQ32307@mit.edu> <20090325235041.GA11024@duck.suse.cz> <20090326090630.GA9369@elte.hu> <20090326113705.GV32307@mit.edu> <20090326140312.GB14822@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090326140312.GB14822@elte.hu> User-Agent: Mutt/1.5.18 (2008-05-17) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@mit.edu X-SA-Exim-Scanned: No (on thunker.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1697 Lines: 36 On Thu, Mar 26, 2009 at 03:03:12PM +0100, Ingo Molnar wrote: > That's in good deal atime update latencies. We still appear to > default to atime enabled in ext4. > > That's stupid - only around 0.01% of all Linux systems relies on > atime - and even those who rely on it would be well served by > relatime. Why arent the relatime patches upstream? Why isnt it the > default? They have been submitted several times. The relatime patches are upstream. Both noatime and relatime are handled at the VFS layer, not at the per-filesystem level. The reason why it sin't the default is because of a desire for POSIX compliance, I suspect. Most distributions are putting relatime into /etc/fstab by default, but we haven't changed the mount option. It wouldn't be hard to add an "atime" option to turn on atime updates, and make either "noatime" or "relatime" the default. This is a simple patch to fs/namespace.c > Atime in its current mandatory do-a-write-for-every-read form is a > stupid relic and we have been paying the fool's tax for it in the > past 10 years. No argument here. I use noatime, myself. It actually saves a lot more than relatime, and unless you are using mutt with local Maildir delivery, relatime isn't really that helpful, and the benefit of noatime is roughly double that of relatime vs normal atime update, in my measurements: http://thunk.org/tytso/blog/2009/03/01/ssds-journaling-and-noatimerelatime/ - Ted -- 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/