linux-kernel - Re: [PATCH 1/7] block: Add block_flush

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Date:	Mon, 30 Mar 2009 16:15:08 -0400
From:	Chris Mason <chris.mason@...cle.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Jeff Garzik <jeff@...zik.org>, Jens Axboe <jens.axboe@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>, Christoph Hellwig <hch@...radead.org>,
	Theodore Tso <tytso@....edu>, Ingo Molnar <mingo@...e.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>, David Rees <drees76@...il.com>,
	Jesper Krogh <jesper@...gh.cc>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	david@...morbit.com, tj@...nel.org
Subject: Re: [PATCH 1/7] block: Add block_flush_device()

On Mon, 2009-03-30 at 22:09 +0200, Andi Kleen wrote:
> Chris Mason <chris.mason@...cle.com> writes:
> >
> > As far as I know, reiserfs is the only one actively using it to choose
> > different code.  It moves a single wait_on_buffer when barriers are on,
> > which I took out once to simplify the code.  Ric saw it in some
> > benchmark numbers and I put it back in.
> >
> > Given that it was a long time ago, I don't have a problem with changing
> > it to work like all the other filesystems.
> 
> When it was a win on reiserfs back then maybe it would be a win
> on ext4 or xfs today too?

It could be, but you get into some larger changes.  The theory behind
the code was that writeback cache is on, so wait_on_buffer isn't really
going to give you a worthwhile error return anyway.  Might as well do
the wait_on_buffer some time later and fix up the commit blocks if it
didn't work out.

We're still arguing about barriers being a good idea all these years
later, and the drives are better at them than they used to be.  So, I'd
rather see less complex code in the filesystems than more.

-chris


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