linux-ext4 - Re: [PATCH] ext4: don't give the "disabling delalloc" if not explicitly specified

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Date:	Mon, 15 Aug 2011 20:13:45 +0200 (CEST)
From:	Lukas Czerner <lczerner@...hat.com>
To:	"Ted Ts'o" <tytso@....edu>
cc:	Eric Sandeen <sandeen@...hat.com>,
	Lukas Czerner <lczerner@...hat.com>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: don't give the "disabling delalloc" if not explicitly
 specified

On Mon, 15 Aug 2011, Ted Ts'o wrote:

> On Mon, Aug 15, 2011 at 10:59:02AM -0500, Eric Sandeen wrote:
> > 
> > The giant behavior-options switch in ext4 is confusing enough; if enabling
> > one option disables another default option, I think that explicitly stating
> > it in the logs is useful.  Doing so silently just covers up the behavior.
> > 
> > If users are unhappy with the message, it's probably more because of 
> > the fact of the matter, and not because of the presentation of the fact.  :)
> 
> Most users probably have no idea what "delalloc" actually means.  So
> when they get a message that saying that data=journalled has disabled
> delalloc, it could easily be seen as noise.  I was moved to do it
> because I got tired of seeing the message over, and over, and over
> again when running xfstests.

So the actual users of data=journal does not care all that much about
it apparently. If the information for some of the users is "noise" than
be it, there is a lot of "noise" in the logs but it is useful for people
who do understand it, or to people who can search for it.

> 
> Maybe an improvement would be (1) to document what data=journal
> implies in the Documentation/filesystems/ext4.txt, (2) change the
> message to explicitly say "delayed allocation" instead of "delalloc"
> (although many people won't have any idea what "delayed allocation"
> means either), and (3) make it a printk_once thing.

That information actually already is in
Documentation/filesystems/ext4.txt but not in the Options section.
However important is to have this information in mount man page, because
that is where usually users go for info right ?

I like the "delayed allocation" version of the warning, but I do not
think we should do it with printk_once as it seems even more confusing
to me.

> 
> I guess I don't agree with the fundamental presumption which is that
> users should be looking at the dmesg output to understand what various
> things mean, and if they didn't explicitly specify delalloc, why
> should we complain about the fact that both delalloc and data=journal
> were specified (when in fact it wasn't specified).

Yeah, we should probably say that we are "disabling delayed allocation".

> 
> 						- Ted
> 

Thanks!
-Lukas
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