linux-kernel - Re: [patch] mm: speedup in __early_pfn_to

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Date:	Fri, 22 Mar 2013 08:25:32 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Russ Anderson <rja@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com
Subject: Re: [patch] mm: speedup in __early_pfn_to_nid


* David Rientjes <rientjes@...gle.com> wrote:

> On Thu, 21 Mar 2013, Ingo Molnar wrote:
> 
> > > Index: linux/mm/page_alloc.c
> > > ===================================================================
> > > --- linux.orig/mm/page_alloc.c	2013-03-18 10:52:11.510988843 -0500
> > > +++ linux/mm/page_alloc.c	2013-03-18 10:52:14.214931348 -0500
> > > @@ -4161,10 +4161,19 @@ int __meminit __early_pfn_to_nid(unsigne
> > >  {
> > >  	unsigned long start_pfn, end_pfn;
> > >  	int i, nid;
> > > +	static unsigned long last_start_pfn, last_end_pfn;
> > > +	static int last_nid;
> > 
> > Please move these globals out of function local scope, to make it more 
> > apparent that they are not on-stack. I only noticed it in the second pass.
> 
> The way they're currently defined places these in meminit.data as 
> appropriate; if they are moved out, please make sure to annotate their 
> definitions with __meminitdata.

I'm fine with having them within the function as well in this special 
case, as long as a heavy /* NOTE: ... */ warning is put before them - 
which explains why these SMP-unsafe globals are safe.

( That warning will also act as a visual delimiter that breaks the 
  normally confusing and misleading 'globals mixed amongst stack 
  variables' pattern. )

Thanks,

	Ingo
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