Re: [RFC][PATCH 2/7] ia64 generic PAGE_SIZE

[Dave Hansen <haveblue@us.ibm.com>]

On Mon, 2006-08-28 at 10:04 -0700, Christoph Lameter wrote:
> On Mon, 28 Aug 2006, Dave Hansen wrote:
> > -config IA64_PAGE_SIZE_64KB
> > -     depends on !ITANIUM
> > -     bool "64KB"
> > -
> > -endchoice
> 
> Uhh.. arch specific stuff in mm/Kconfig. Each arch needs to modify the 
> mm/Kconfig?

Yes and no.  First of all, 15 of the 24 architectures use the Kconfig
default of 4k pages.  Anybody adding an architecture with 4k pages only
has to include asm-generic/page.h in their arch, and they don't add
*anything* to Kconfig.  If they want completely fixed page sizes other
than 4k, they only add '|| ARCH' on one line in the Kconfig.

There are a couple of ways to go about enabling the configurable page
sizes.  One is to do what I did, hand have all of the architectures
enumerated in mm/Kconfig.  The other is to have something along the
lines of:

        choice
                prompt "Kernel Page Size"
                depends on ARCH_CHOOSES_PAGE_SIZE
        	...
        
Then in arch/{ia64,...}/Kconfig, have
        
        config ARCH_CHOOSES_PAGE_SIZE
        	def_bool y
        
That would be easy enough to do.  However, what I wanted to get out of
this was to be able to look at mm/Kconfig and get a really nice overview
of what *everybody* is doing.  I'd be more inclined to do the
ARCH_CHOOSES... stuff if the architecture-specific conditions were
actually complicated.  They really aren't.

Admittedly, this is a bit different from how it has been done
traditionally, but is is a really great tool for anyone working on
arch-generic code that wants to know "what architectures have an 8k page
size", or "what arches have a configurable page size".  This makes one
place to go look, with zero grepping.  

> Also cc linux-ia64@vger.kernel.org on these. 

Sure thing.

-- Dave

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