linux-kernel - Re: [PATCH] [7/8] CPA: Implement GBpages support in change_page

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Message-Id: <200801192027.46689.ak@suse.de>
Date:	Sat, 19 Jan 2008 20:27:46 +0100
From:	Andi Kleen <ak@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	tglx@...utronix.de, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] [7/8] CPA: Implement GBpages support in change_page_attr()

On Saturday 19 January 2008 19:53:14 Ingo Molnar wrote:
> 
> * Andi Kleen <ak@...e.de> wrote:
> 
> >  arch/x86/mm/pageattr_64.c | 150 
> >  ++++++++++++++++++++++++++++++++++++----------
> >  1 file changed, 119 insertions(+), 31 deletions(-)
> 
> please unify the files first, we dont want to let pageattr_32.c and 
> pageattr_64.c diverge even more. Once we get these files unified we 
> layer more features ontop of it. 

They work significantly differently in a few important areas (e.g. particularly 
regarding NX  handling and the kernel mapping) Off the top of my 
head I don't know of a clean way to unify them. 32bit and 64bit kernel 
mappings differ in many significant ways. Maybe it's possible, but it's 
certainly not something I would want to tackle short term in a hurry.
The kernel mappings between 32bit and 64bit are quite different.

However I would like GBPAGES definitely to make the .25 merge window
and they won't work without the upgraded c_p_a().

So please reconsider.

> While gbpages is not available on  
> 32-bit and probably wont ever be, this code has been historically very 
> fragile, 

I'm sure a hurried up unification would make it even more fragile.

-Andi
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