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Date: Tue, 29 May 2007 11:36:51 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
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To: Mel Gorman <mel@csn.ul.ie>
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       kamezawa.hiroyu@jp.fujitsu.com
Subject: Re: [PATCH 3/7] Allow CONFIG_MIGRATION to be set without CONFIG_NUMA
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On Tue, 29 May 2007, Mel Gorman wrote:

> > > +config SYSCALL_MOVE_PAGES
> > > +	def_bool y
> > > +	depends on MIGRATION && NUMA
> > > +
> > 
> > Do we really need the CONFIG_SYSCALL_MOVE_PAGES? I think you will directly
> > access the lower levels. So why have it? CONFIG_SYSCALL_MOVE_PAGES ==
> > CONFIG_NUMA.
> 
> Without SYSCALL_MOVE_PAGES, the check in migrate.h becomes
> 
> #if defined(CONFIG_NUMA) && defined(CONFIG_MIGRATION)
> /* Check if a vma is migratable */
> static inline int vma_migratable(struct vm_area_struct *vma)
> #endif

Why do you need vma_migratable for the CONFIG_MIGRATION case? The use of 
vma_migratable in a !NUMA sitation would not be working right as far as I 
can tell.

#ifdef CONFIG_NUMA

is fine.

> That in itself is fine but in mm/migrate.c I didn't want to define
> sys_move_pages() in the non-NUMA case. Whatever about the header file where
> SYSCALL_MOVE_PAGES obscures understanding, I think it makes sense to have
> SYSCALL_MOVE_PAGES for mm/migrate.c . What do you think?

Why do you need sys_move_pages for the non-NUMA case?

The low level function that I intended to be used by defrag is 
migrate_pages and that one is outside of #ifdef CONFIG_NUMA.