linux-kernel - Re: [PATCH 9/9] mm: Remove ifdef condition in include/linux/mm.h

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Message-Id: <20140207143050.6bd35ed5c670a3ca143ba59a@linux-foundation.org>
Date:	Fri, 7 Feb 2014 14:30:50 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Josh Triplett <josh@...htriplett.org>,
	Rashika Kheria <rashika.kheria@...il.com>,
	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Jiang Liu <jiang.liu@...wei.com>,
	Michel Lespinasse <walken@...gle.com>, linux-mm@...ck.org
Subject: Re: [PATCH 9/9] mm: Remove ifdef condition in include/linux/mm.h

On Fri, 7 Feb 2014 13:15:29 -0800 (PST) David Rientjes <rientjes@...gle.com> wrote:

> On Fri, 7 Feb 2014, Josh Triplett wrote:
> 
> > > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > > index 1cedd00..5f8348f 100644
> > > > --- a/include/linux/mm.h
> > > > +++ b/include/linux/mm.h
> > > > @@ -1589,10 +1589,8 @@ static inline int __early_pfn_to_nid(unsigned long pfn)
> > > >  #else
> > > >  /* please see mm/page_alloc.c */
> > > >  extern int __meminit early_pfn_to_nid(unsigned long pfn);
> > > > -#ifdef CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID
> > > >  /* there is a per-arch backend function. */
> > > >  extern int __meminit __early_pfn_to_nid(unsigned long pfn);
> > > > -#endif /* CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID */
> > > >  #endif
> > > >  
> > > >  extern void set_dma_reserve(unsigned long new_dma_reserve);
> > > 
> > > Wouldn't it be better to just declare the __early_pfn_to_nid() in 
> > > mm/page_alloc.c to be static?
> > 
> > Won't that break the ability to override that function in
> > architecture-specific code (as arch/ia64/mm/numa.c does)?
> > 
> 
> Why?  CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID should define where this function 
> is defined so ia64 should have it set and the definition which I'm 
> suggesting be static is only compiled when this is undefined in 
> mm/page_alloc.c.  I'm not sure why we'd want to be messing with the 
> declaration?

__early_pfn_to_nid() must be global if it is implemented in arch/. 

Making it static when it is implemented in core mm makes a bit of
sense, in that it cleans up the non-ia64 namespace and discourages
usage from other compilation units.  But it's is a bit odd and
unexpected to do such a thing.  I'm inclined to happily nuke the ifdef
then go think about something else ;)




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