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:

quoted

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