linux-kernel - Re: [PATCH 5/6] introduce pmd_to_pte

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Date:	Wed, 15 Feb 2012 16:54:08 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	linux-mm@...ck.org, David Rientjes <rientjes@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] introduce pmd_to_pte_t()

On Wed,  8 Feb 2012 10:51:41 -0500
Naoya Horiguchi <n-horiguchi@...jp.nec.com> wrote:

> Casting pmd into pte_t to handle thp is strongly architecture dependent.
> This patch introduces a new function to separate this dependency from
> independent part.
> 
>
> ...
>
> --- 3.3-rc2.orig/include/asm-generic/pgtable.h
> +++ 3.3-rc2/include/asm-generic/pgtable.h
> @@ -434,6 +434,10 @@ static inline int pmd_trans_splitting(pmd_t pmd)
>  {
>  	return 0;
>  }
> +static inline pte_t pmd_to_pte_t(pmd_t *pmd)
> +{
> +	return 0;
> +}

This doesn't compile.

And I can't think of a sensible way of generating a stub for this
operation - if you have a pmd_t and want to convert it to a pte_t then
just convert it, dammit.  And there's no rationality behind making that
conversion unavailable or inoperative if CONFIG_TRANSPARENT_HUGEPAGE=n?

Shudder.  I'll drop the patch.  Rethink, please.
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