linux-kernel - Re: Is nobh code still useful?

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Message-ID: <20090918141226.GB26991@mit.edu>
Date:	Fri, 18 Sep 2009 10:12:26 -0400
From:	Theodore Tso <tytso@....edu>
To:	Badari Pulavarty <pbadari@...ibm.com>
Cc:	Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Is nobh code still useful?

On Thu, Sep 17, 2009 at 09:21:37PM -0700, Badari Pulavarty wrote:
>
> Originally it was supported on ext2. I added support nobh support for  
> ext3. At that time, the main
> issue/complaint was that, these bufferheads consume memory from  
> ZONE_NORMAL causing
> memory pressure on 32-bit (i386) configurations.

Specifically, it matters on very large configuration systems (i.e.,
32GB-64GB using PAE-36) that today we'd probably just say, "use
x86_64, you moron".  It would probably matter if someone were to want
to upgrade a non-64-bit capable machine to a newer kernel.  

Dropping nobh from ext3 at this point might prevent some of these
older systems from upgrading, I'm not sure how much we would care; on
the one hand, these machines tended to be pretty expensive, so people
would probably want to use them for a while.  On the other hand, it
has been over five years now since x86_64 machines have been
available, and many of these customers are highly unlikely to want to
upgrade anyway.

						- Ted

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