Re: Enable asynchronous commits by default patch revoked?

[Theodore Tso <tytso@mit.edu>]

On Wed, Sep 02, 2009 at 10:48:33AM -0400, Tom Vier wrote:
> On Mon, Aug 24, 2009 at 06:07:39PM -0400, Theodore Tso wrote:
> > Sure, agreed.  But let's look a bit closer at what "async commit"
> > really means.
> > 
> > What ext3 and ext4 does by default is this:
> > 
> > 1)  Write data blocks required by data=ordered mode (if any)
> 
> Shouldn't there be a write barrier after data blocks, so that the journal
> blocks aren't written first? ie, mark the first journal block write with
> barrier flag on.

No, it doesn't matter, because the journal blocks are ignored until
the commit block is written.  So the order of the data blocks required
by data=ordered mode, and the journal blocks are written can be freely
reordered by the elevator and the hard drive without any risk of data
integrity problems.

						- Ted