Date: Thu, 26 Mar 2009 14:47:34 +0000 (GMT)
From: Hugh Dickins <hugh@veritas.com>
To: Jens Axboe <jens.axboe@oracle.com>
cc: Ric Wheeler <rwheeler@redhat.com>, Jeff Garzik <jeff@garzik.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Theodore Tso <tytso@mit.edu>, Ingo Molnar <mingo@elte.hu>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Arjan van de Ven <arjan@infradead.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, Nick Piggin <npiggin@suse.de>,
       David Rees <drees76@gmail.com>, Jesper Krogh <jesper@krogh.cc>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Linux 2.6.29
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On Thu, 26 Mar 2009, Jens Axboe wrote:
> On Wed, Mar 25 2009, Hugh Dickins wrote:
> > 
> > Tangential question, but am I right in thinking that BIO_RW_BARRIER
> > similarly bars across all partitions, whereas its WRITE_BARRIER and
> > DISCARD_BARRIER users would actually prefer it to apply to just one?
> 
> All the barriers refer to just that range which the barrier itself
> references.

Ah, thank you: then I had a fundamental misunderstanding of them,
and need to go away and work that out some more.

Though I didn't read it before asking, doesn't the I/O Barriers section
of Documentation/block/biodoc.txt give a very different impression?

> The problem with the full device flushes is implementation
> on the hardware side, since we can't do small range flushes. So it's not
> as-designed, but rather the best we can do...

Right, that part of it I did get.

Hugh
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