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Date: Mon, 19 May 2008 10:46:54 -0400
From: Theodore Tso <tytso@MIT.EDU>
To: Chris Mason <chris.mason@oracle.com>
Cc: Andi Kleen <andi@firstfloor.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Eric Sandeen <sandeen@redhat.com>, linux-ext4@vger.kernel.org,
       linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
       jamie@shareable.org
Subject: Re: [PATCH 0/4] (RESEND) ext3[34] barrier changes
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On Mon, May 19, 2008 at 09:26:41AM -0400, Chris Mason wrote:
> >
> > Didn't ext4 have some new checksum trick to avoid them?
> 
> I didn't think checksumming avoided barriers completely.  Just the barrier 
> before the commit block, not the barrier after.

Funny thing, I was looking in this over the weekend.  It currently
avoids barriers entirely if journal_async_commit is enabled (which is
not the default); if enabled, it effectively forces barrier=0.  This
is IMHO a bug.

I'm working on a patch where "barrier=1" will use a barrier before and
after, and "barrier=1,journal_async_commit" will use a barrier after.

       	   				    	     - Ted