Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759397AbZC3TKn (ORCPT ); Mon, 30 Mar 2009 15:10:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759361AbZC3TKQ (ORCPT ); Mon, 30 Mar 2009 15:10:16 -0400 Received: from srv5.dvmed.net ([207.36.208.214]:38796 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759362AbZC3TKO (ORCPT ); Mon, 30 Mar 2009 15:10:14 -0400 Message-ID: <49D118E5.4060209@garzik.org> Date: Mon, 30 Mar 2009 15:09:25 -0400 From: Jeff Garzik User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Jens Axboe CC: Bartlomiej Zolnierkiewicz , =?ISO-8859-1?Q?Fernan?= =?ISO-8859-1?Q?do_Luis_V=E1zquez_Cao?= , 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 References: <49D0B535.2010106@oss.ntt.co.jp> <49D0B978.5030107@oss.ntt.co.jp> <200903301714.13174.bzolnier@gmail.com> <20090330175121.GW5178@kernel.dk> <49D10797.9080306@garzik.org> <20090330175953.GY5178@kernel.dk> In-Reply-To: <20090330175953.GY5178@kernel.dk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Score: -4.4 (----) X-Spam-Report: SpamAssassin version 3.2.5 on srv5.dvmed.net summary: Content analysis details: (-4.4 points, 5.0 required) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1769 Lines: 38 Jens Axboe wrote: > On Mon, Mar 30 2009, Jeff Garzik wrote: >> Jens Axboe wrote: >>> 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. >> How do installers and/or kernels detect a battery-backed cache that does >> not need flush? > > They obviously can't, otherwise it would not be an issue at all. And > whether it's an issue is up for debate, until someone can point at such > a device. You could add a white/blacklist. Sorry, I guess I misinterpreted your dual "IFF" statement :) I completely agree that the suggested knob, for disabling cache flush for these battery-backed devices, is at the present time addressing an entirely theoretical argument AFAICS. Jeff -- 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/