Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756139AbZC3R4c (ORCPT ); Mon, 30 Mar 2009 13:56:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753192AbZC3R4W (ORCPT ); Mon, 30 Mar 2009 13:56:22 -0400 Received: from srv5.dvmed.net ([207.36.208.214]:56840 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753474AbZC3R4W (ORCPT ); Mon, 30 Mar 2009 13:56:22 -0400 Message-ID: <49D10797.9080306@garzik.org> Date: Mon, 30 Mar 2009 13:55:35 -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> In-Reply-To: <20090330175121.GW5178@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: 1241 Lines: 29 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? 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/