Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756448AbZC3Rvl (ORCPT ); Mon, 30 Mar 2009 13:51:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753968AbZC3RvZ (ORCPT ); Mon, 30 Mar 2009 13:51:25 -0400 Received: from brick.kernel.dk ([93.163.65.50]:39286 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753221AbZC3RvY (ORCPT ); Mon, 30 Mar 2009 13:51:24 -0400 Date: Mon, 30 Mar 2009 19:51:21 +0200 From: Jens Axboe To: Bartlomiej Zolnierkiewicz Cc: Fernando Luis =?iso-8859-1?Q?V=E1zquez?= Cao , Jeff Garzik , Christoph Hellwig , Linus Torvalds , Theodore Tso , Ingo Molnar , Alan Cox , Arjan van de Ven , Andrew Morton , Peter Zijlstra , Nick Piggin , David Rees , Jesper Krogh , Linux Kernel Mailing List , chris.mason@oracle.com, david@fromorbit.com, tj@kernel.org Subject: Re: [PATCH 5/7] vfs: Add wbcflush sysfs knob to disable storage device writeback cache flushes Message-ID: <20090330175121.GW5178@kernel.dk> References: <49D0B535.2010106@oss.ntt.co.jp> <49D0B978.5030107@oss.ntt.co.jp> <200903301714.13174.bzolnier@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <200903301714.13174.bzolnier@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1346 Lines: 30 On Mon, Mar 30 2009, Bartlomiej Zolnierkiewicz wrote: > On Monday 30 March 2009, Fernando Luis V?zquez Cao wrote: > > Add a sysfs knob to disable storage device writeback cache flushes. > > The horde of casual desktop users (with me included) would probably prefer > having two settings -- one for filesystem barriers and one for fsync(). > > IOW I prefer higher performance at the cost of risking losing few last > seconds/minutes of work in case of crash / powerfailure but I would still > like to have the filesystem in the consistent state after such accident. The knob is meant to control whether we really need to send a flush to the device or not, so it's an orthogonal issue to what you are talking about. For battery backed caches, we never need to flush. This knob is useful IFF we have devices with write back caches that STILL do a cache flush. As such, I'd also prefer waiting with adding such a knob until such a device has actually be observed. No point in adding something just in case it may exist. And even then, it's probably even better handled in the driver. -- 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/