Date: Mon, 27 Oct 2008 12:57:00 +0100
From: Jens Axboe <jens.axboe@oracle.com>
To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>,
       linux-kernel@vger.kernel.org, mingo@elte.hu
Subject: Re: [PATCH 2/2] x86: replace BIO_VMERGE_BOUNDARY with BIOVEC_PHYS_MERGEABLE
Message-ID: <20081027115659.GZ22217@kernel.dk>
References: <49057A15.7030007@goop.org> <20081027173739Q.fujita.tomonori@lab.ntt.co.jp> <49058774.3030506@goop.org> <20081027183604V.fujita.tomonori@lab.ntt.co.jp> <20081027094111.GU22217@kernel.dk> <4905A961.9000603@goop.org>
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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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