Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263601AbUCUJna (ORCPT ); Sun, 21 Mar 2004 04:43:30 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263622AbUCUJna (ORCPT ); Sun, 21 Mar 2004 04:43:30 -0500 Received: from ns.virtualhost.dk ([195.184.98.160]:21165 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S263601AbUCUJn2 (ORCPT ); Sun, 21 Mar 2004 04:43:28 -0500 Date: Sun, 21 Mar 2004 10:43:25 +0100 From: Jens Axboe To: Bartlomiej Zolnierkiewicz Cc: Chris Mason , Jeff Garzik , Linux Kernel Subject: Re: [PATCH] barrier patch set Message-ID: <20040321094324.GC1627@suse.de> References: <20040319153554.GC2933@suse.de> <200403201805.26211.bzolnier@elka.pw.edu.pl> <1079802604.11058.292.camel@watt.suse.com> <200403202116.57949.bzolnier@elka.pw.edu.pl> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200403202116.57949.bzolnier@elka.pw.edu.pl> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1674 Lines: 37 On Sat, Mar 20 2004, Bartlomiej Zolnierkiewicz wrote: > On Saturday 20 of March 2004 18:10, Chris Mason wrote: > > On Sat, 2004-03-20 at 12:05, Bartlomiej Zolnierkiewicz wrote: > > > On Saturday 20 of March 2004 17:32, Chris Mason wrote: > > > > On Sat, 2004-03-20 at 11:23, Bartlomiej Zolnierkiewicz wrote: > > > > > > > - why are we doing pre-flush? > > > > > > > > The journaled filesystems need this. We need to make sure that before > > > > we write the commit block for a transaction, all the previous log > > > > blocks we're written are safely on media. Then we also need to make > > > > sure the commit block is on media. > > > > > > For low-level driver it shouldn't really matter whether sectors to be > > > written are the commit block for a transaction or the previous log blocks > > > and in the current implementation it does matter. > > > > As Jens said, it depends on how you define barrier ;-) I define it as > > this io will be written after all the previous io and before any later > > io. It was originally written with scsi tags in mind as well, the FS > > side was the same for both. > > Yes, thanks for explaining this. > > I took a quick look at fs/jbd/ and now I think I understand the way barriers > currently work. I assume that SCSI handles barriers by ordered tags, right? That's the idea, yes. Needs some SCSI error handling work though, to always ensure correct ordering. -- Jens Axboe - 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/