Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753542AbZC3SAM (ORCPT ); Mon, 30 Mar 2009 14:00:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752572AbZC3R75 (ORCPT ); Mon, 30 Mar 2009 13:59:57 -0400 Received: from brick.kernel.dk ([93.163.65.50]:45378 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752324AbZC3R74 (ORCPT ); Mon, 30 Mar 2009 13:59:56 -0400 Date: Mon, 30 Mar 2009 19:59:53 +0200 From: Jens Axboe To: Jeff Garzik Cc: Bartlomiej Zolnierkiewicz , Fernando Luis =?iso-8859-1?Q?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 Message-ID: <20090330175953.GY5178@kernel.dk> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <49D10797.9080306@garzik.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1626 Lines: 36 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. So either that knob has to be turned by an administrator (yeah...), or the in-kernel info would have to be updated. Or a udev rule. -- 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/