From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759545AbZBMGIT (ORCPT ); Fri, 13 Feb 2009 01:08:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750928AbZBMGIJ (ORCPT ); Fri, 13 Feb 2009 01:08:09 -0500 Received: from mx2.redhat.com ([66.187.237.31]:58462 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750876AbZBMGII (ORCPT ); Fri, 13 Feb 2009 01:08:08 -0500 Message-ID: <49950E1E.8040307@redhat.com> Date: Fri, 13 Feb 2009 00:07:26 -0600 From: Eric Sandeen User-Agent: Thunderbird 2.0.0.19 (Macintosh/20081209) MIME-Version: 1.0 To: =?ISO-8859-1?Q?Fernando_Luis_V=E1zquez_Cao?= CC: Jan Kara , Theodore Tso , Alan Cox , Pavel Machek , kernel list , Jens Axboe , fernando@kic.ac.jp, Ric Wheeler Subject: Re: vfs: Add MS_FLUSHONFSYNC mount flag References: <1232114101.13775.63.camel@sebastian.kern.oss.ntt.co.jp> <20090116163039.GE10617@duck.suse.cz> <1232185639.4831.18.camel@sebastian.kern.oss.ntt.co.jp> <1232186449.4831.29.camel@sebastian.kern.oss.ntt.co.jp> <20090119120349.GA10193@duck.suse.cz> <1233135913.5399.57.camel@sebastian.kern.oss.ntt.co.jp> <20090128095518.GA16554@duck.suse.cz> <1234434811.15270.7.camel@sebastian.kern.oss.ntt.co.jp> <1234434970.15433.4.camel@sebastian.kern.oss.ntt.co.jp> <499458C1.90105@redhat.com> <20090212212304.GA7935@duck.suse.cz> <499494E2.3060006@redhat.com> <1234489622.3795.49.camel@sebastian.kern.oss.ntt.co.jp> In-Reply-To: <1234489622.3795.49.camel@sebastian.kern.oss.ntt.co.jp> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Fernando Luis Vázquez Cao wrote: > On Thu, 2009-02-12 at 15:30 -0600, Eric Sandeen wrote: >> Jan Kara wrote: >>> On Thu 12-02-09 11:13:37, Eric Sandeen wrote: >> ... >> >>>> Also that way if you have 8 partitions on a battery-backed blockdev, you >>>> can tune it once, instead of needing to mount all 8 filesystems with the >>>> new option. >>> Yes, but OTOH we should give sysadmin a possibility to enable / disable >>> it on just some partitions. I don't see a reasonable use for that but people >>> tend to do strange things ;) and here isn't probably a strong reason to not >>> allow them. >>> >>> Honza >> But nobody has asked for that, have they? So why offer it up a this point? >> >> They could use LD_PRELOAD to make fsync a no-op if they really don't >> care for it, I guess... though that's not easily per-fs either. >> >> But do we really want to go out of our way to enable people to >> short-circuit data integrity paths and then file bugs when their files >> go missing? :) > > Well, it is just a matter of using safe defaults. IMHO, a scenario where > the administrator wants to optimize writes to a certain partition and > _explicitly_ clears MS_FLUSHONFSYNC on that superblock is not completely > unreasonable. One case is "this device is safe with a write cache and flush is not necessary for data consistency" - that's the per-bdev setting. The other case is "I don't really care and I just want to go faster" - that's the per-mount setting. I'd be much more likely to support the first case, as it's needed for maximum performance w/o sacrificing correctness, when properly used. The latter case is really only for cutting corners and giving people more rope than they need to hang themselves. >> (I guess the blockdev tunable is similarly dangerous, but it more >> clearly meets the explicit need (writecache-safe devices)) > > If distributions use sane defaults and we document the mount option or > bdev tunable properly I guess it might make sense to allow system > administrators to shoot themselves in the foot. > > (By the way, in this patch-set a patch for mount(8) is included.) ... one of the advantages of making it a bdev tunable is that you don't have to mess with mount(8) :) -Eric