linux-kernel - Re: [patch 09/10] Hugetlb common code update for System z.

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Message-Id: <1206719599.6592.10.camel@localhost>
Date:	Fri, 28 Mar 2008 16:53:19 +0100
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>, haveblue@...ibm.com,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Tony Luck <tony.luck@...el.com>,
	Paul Mackerras <paulus@...ba.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Mundt <lethal@...ux-sh.org>
Subject: Re: [patch 09/10] Hugetlb common code update for System z.

On Fri, 2008-03-28 at 15:06 +0100, Ingo Molnar wrote:
> * Gerald Schaefer <gerald.schaefer@...ibm.com> wrote:
> 
> >  include/asm-sh/hugetlb.h      |   28 +++++++++++++++++++++++++
> >  include/asm-sparc64/hugetlb.h |   30 +++++++++++++++++++++++++++
> >  include/asm-x86/hugetlb.h     |   28 +++++++++++++++++++++++++
> 
> these seem largely duplicated - shouldnt there be an 
> asm-generic/hugetlb.h instead, which asm/hugetlb.h could include to get 
> default behavior? It would probably reduce the linecount of your patch 
> as well.

Well the hugetlbfs primitives are architecture specific, aren't they?
Just like the other page table manipulation functions. I find the usual
method to use asm-generic/<xxx> and a lot of defines and #ifdefs to pick
up the correct definition from a generic header file rather hard to
read. In the end each arch that wants to use hugetlbfs has to define
each of the hugetlb primitives. Most of them are rather simple, e.g. the
x86 set_huge_pte_at is just a set_pte_at. One line to define the
primitive. Now we could have an #ifdef block around the default
definition that maps set_huge_pte_at to set_pte_at in asm-generic and an
ARCH_HAS_xx override for architecture that need to do something more
complicated. Somehow that was where we started ..
I think the best way to get rid of the ARCH_HAS_xxx fugliness is to let
each architecture define their primitives, even if it looks like code
duplication.

-- 
blue skies,
  Martin.

"Reality continues to ruin my life." - Calvin.

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