From: Eric Sandeen Subject: Re: [PATCH] ext4: add fallocate mode blocking for debugging purposes Date: Tue, 15 Apr 2014 14:13:59 -0500 Message-ID: <534D84F7.30003@redhat.com> References: <1397420518-29218-1-git-send-email-tytso@mit.edu> <20140413220016.GD8122@thunk.org> <534D5B2D.70408@redhat.com> <20140415184442.GC4456@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: =?windows-1252?Q?Luk=E1=9A_Czerner?= , Ext4 Developers List , Namjae Jeon To: "Theodore Ts'o" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:25969 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751012AbaDOTOD (ORCPT ); Tue, 15 Apr 2014 15:14:03 -0400 In-Reply-To: <20140415184442.GC4456@thunk.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 4/15/14, 1:44 PM, Theodore Ts'o wrote: > On Tue, Apr 15, 2014 at 11:15:41AM -0500, Eric Sandeen wrote: >> >> I tend to agree, better to fix the kernel than to add a knob to turn it >> off. And fsx changes can happen a lot quicker than kernel changes. [1] >> >> And if it's really unsafe, and you really want to add a knob, I'd at least >> default it to off until it's non-corrupting, and add a message that >> this tunable will go away as soon as it's stable, so you'll have no >> qualms about quickly deprecating it... > > Yeah, I went back and forth on this. One of there reasons why I added > a kernel knob is that *I* can make the kernel change a lot faster than > it would be to tweak all of the various xfstests program to globally > disable certain operations in fsx, fstress, etc. > > I also had a sneaking suspicion that we might have a similar issue > with the INSERT RANGE patches which are coming down the pike, and so > having a general way of also being able INSERT RANGE if to be able to > quickly determine whether a potential bug was caused by INSERT RANGE > or some other pending changes might also be useful. > > I freely admit it is a bit of a hack, though. Does the hack smell > less bad if we wrap it in CONFIG_EXT4FS_DEBUG? > >> [1] it'd be nifty to make an env. var in xfstests which can globally >> disable certain fsx operations across all tests which run fsx... > > Yes, although as I mentioned above, it would be really nice if it > worked across all of the various tests, and not just be limited to > fsx, or even just fsx and fstress. Well, for tests which are specific to collapse range, it'd be trivial to add a "collapse" group, and exclude it. For generic stress tests which happen to do collapse range, it'd take a bit more. But that'd probably still be the generic solution. XFS got bitten too, there were collapse range problems. But the fixes are already in the pipe AFAIK. -Eric > - Ted > > >