Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759048AbZC1TyE (ORCPT ); Sat, 28 Mar 2009 15:54:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759210AbZC1TwT (ORCPT ); Sat, 28 Mar 2009 15:52:19 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:40835 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759227AbZC1TwR (ORCPT ); Sat, 28 Mar 2009 15:52:17 -0400 Date: Sat, 28 Mar 2009 12:43:03 -0700 From: Andrew Morton To: Linus Torvalds Cc: Jan Kara , Ingo Molnar , Theodore Tso , 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: <20090328124303.d902fb57.akpm@linux-foundation.org> In-Reply-To: References: <20090325185824.GO32307@mit.edu> <20090325215137.GQ32307@mit.edu> <20090325235041.GA11024@duck.suse.cz> <20090326090630.GA9369@elte.hu> <20090326181106.GC17159@duck.suse.cz> <20090326155725.c2150ab2.akpm@linux-foundation.org> <20090327213806.GG31071@duck.suse.cz> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.5; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1266 Lines: 29 On Fri, 27 Mar 2009 15:10:56 -0700 (PDT) Linus Torvalds wrote: > On Fri, 27 Mar 2009, Jan Kara wrote: > > > > Doable but not fairly simple ;) Firstly you have to restart a transaction > > when you've used up all the credits you originally started with (easy), > > secondly ext3 uses lock order PageLock -> "transaction start" which is > > unusable for the scheme you suggest. So we'd have to revert that - which > > needs larger audit of our locking scheme and that's probably the reason > > why noone has done it yet. > > It's also not clear that ext3 can really do much better than the regular > generic_writepages() logic. I mean, seriously, what's there to improve on? - opening a single transaction for many pages in the cases when a transaction _is_ needed. - single large BIO versus zillions of single-page BIOs. Relatively minor benefits, but it's a bit odd that we never got around to doing it. It just got quite a bit harder to do, so I expect we won't be doing it. -- 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/