linux-kernel - Re: [PATCH 2/2] x86: replace BIO_VMERGE_BOUNDARY with BIOVEC_PHYS

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Message-ID: <20081027115659.GZ22217@kernel.dk>
Date:	Mon, 27 Oct 2008 12:57:00 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux-kernel@...r.kernel.org, mingo@...e.hu
Subject: Re: [PATCH 2/2] x86: replace BIO_VMERGE_BOUNDARY with BIOVEC_PHYS_MERGEABLE

On Mon, Oct 27 2008, Jeremy Fitzhardinge wrote:
> Jens Axboe wrote:
> >Pretty much baffles me as well, xen should just need to do
> >
> >#define BIOVEC_PHYS_MERGEABLE(vec1, vec2)       0
> >  
> 
> It needs to be a runtime switch, since we only want to do this when 
> actually running under Xen.  Also, its possible that the two pages might 
> actually be physically contiguous, so they could be merged anyway.

Alright, then add a xen_biovec_phys_mergeable(vec1, vec2) in the xen
code that actually checks this for real. You can add your switch there
as well. Then put the BIOVEC_PHYS_MERGEABLE() in the xen arch includes,
done.

What Tomo is saying is that this has nothing to do with virtual merging,
and he's right.

-- 
Jens Axboe

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