linux-kernel - Re: FW: [PATCH] powerpc/mm: Export HPAGE

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Date:	Wed, 4 Feb 2009 16:00:37 -0500
From:	wli@...ementarian.org
To:	Roland Dreier <rdreier@...co.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Eli Cohen <eli@...lanox.co.il>, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org
Subject: Re: FW: [PATCH] powerpc/mm: Export HPAGE_SHIFT

On Wed, Feb 04, 2009 at 11:11:22AM -0800, Roland Dreier wrote:
> Heh.  Looking into the implementation, it seems that I could actually do
> 	PAGE_SIZE << compound_order(page)
> directly (since there's no reason to go from size to hstate and back to
> size.  I don't know all the details of these VM internals, but that
> seems to only work on the first (small) page of a giant page?  Which
> causes problems for what we're trying to do here...

You should be able to find the head of a compound page using the
compound_head() inline, so try

	PAGE_SIZE << compound_order(compound_head(page))


-- wli
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