linux-ext4 - Re: Help on Implementation of EXT3 type Ordered Mode in EXT4

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Message-ID: <20100209160522.GE15318@atrey.karlin.mff.cuni.cz>
Date:	Tue, 9 Feb 2010 17:05:22 +0100
From:	Jan Kara <jack@...e.cz>
To:	Kailas Joshi <kailas.joshi@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Help on Implementation of EXT3 type Ordered Mode in EXT4

  Hi,

> I recently found that in EXT4 with delayed block the Ordered mode does not
> bahave same as in EXT3.
> I found a patch for this at http://lwn.net/Articles/324023/, but it has some
> journal block estimation problem resulting into deadlock.
> 
> I would like to know if it has been solved.
> If not, is it possible to solve it? What are the complexities involved?
  It has not been solved. The problem is that to commit data on transaction
commit (which is what data=ordered mode has historically done), you have to
allocate space for these blocks. But that allocation needs to modify a
filesystem and thus journal more blocks... And that is tricky - we would have
to reserve space in the current transaction for allocation of delayed data.  So
it gets a bit messy...
  Why exactly do you need the old data=ordered guarantees?

									Honza

-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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