linux-kernel - Re: [PATCH] Fix crash with FLAT_MEMORY and ARCH_PFN

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Message-ID: <20071218123152.GA19536@alpha.franken.de>
Date:	Tue, 18 Dec 2007 13:31:52 +0100
From:	tsbogend@...ha.franken.de (Thomas Bogendoerfer)
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Mel Gorman <mel@....ul.ie>,
	Bob Picco <bob.picco@...com>,
	Dave Hansen <haveblue@...ibm.com>,
	Andy Whitcroft <apw@...dowen.org>, Andi Kleen <ak@....de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Keith Mannthey <kmannth@...il.com>,
	"Luck, Tony" <tony.luck@...el.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yasunori Goto <y-goto@...fujitsu.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] Fix crash with FLAT_MEMORY and ARCH_PFN_OFFSET != 0

On Tue, Dec 18, 2007 at 04:24:04AM -0800, Andrew Morton wrote:
> On Tue, 18 Dec 2007 13:03:00 +0100 (CET) Thomas Bogendoerfer <tsbogend@...ha.franken.de> wrote:
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -3427,7 +3427,7 @@ static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat)
> >  		mem_map = NODE_DATA(0)->node_mem_map;
> >  #ifdef CONFIG_ARCH_POPULATES_NODE_MAP
> >  		if (page_to_pfn(mem_map) != pgdat->node_start_pfn)
> > -			mem_map -= pgdat->node_start_pfn;
> > +			mem_map -= (pgdat->node_start_pfn - ARCH_PFN_OFFSET);
> >  #endif /* CONFIG_ARCH_POPULATES_NODE_MAP */
> >  	}
> >  #endif
> 
> hm.  It's rather non-trivial to verify that this will compile OK on all
> architectures.

I grepped through include/asm-* and found:

#if defined(CONFIG_FLATMEM)

#ifndef ARCH_PFN_OFFSET
#define ARCH_PFN_OFFSET         (0UL)
#endif

in include/asm-generic/memory_model.h. So I'm still confident, that
this works on all architectures. It's tested on MIPS.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessary a
good idea.                                                [ RFC1925, 2.3 ]
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