linux-kernel - Re: [PATCH 1/2] clean up for early_pfn_to

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Date:	Mon, 16 Feb 2009 09:50:42 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Miller <davem@...emloft.net>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, kosaki.motohiro@...fujitsu.com,
	davem@...emlloft.net, heiko.carstens@...ibm.com, stable@...nel.org
Subject: Re: [PATCH 1/2] clean up for early_pfn_to_nid

On Fri, 13 Feb 2009 22:12:26 -0800 (PST)
David Miller <davem@...emloft.net> wrote:

> From: Andrew Morton <akpm@...ux-foundation.org>
> Date: Fri, 13 Feb 2009 14:20:32 -0800
> 
> > I queued these as
> > 
> > mm-clean-up-for-early_pfn_to_nid.patch
> > mm-fix-memmap-init-for-handling-memory-hole.patch
> > 
> > and tagged them as needed-in-2.6.28.x.  I don't recall whether they are
> > needed in earlier -stable releases?
> 
> Every kernel going back to at least 2.6.24 has this bug.  It's likely
> been around even longer, I didn't bother checking.
> 

Sparc64's one is broken from this commit.

09337f501ebdd224cd69df6d168a5c4fe75d86fa
sparc64: Kill CONFIG_SPARC32_COMPAT

CONFIG_NODES_SPAN_OTEHR_NODES is set and config allows following kind of NUMA
This is requirements from powerpc.

low address ---<-   max order     ->---- high address
               [Node0][Node1][Node0]
So, nid is checked at memmap init.

But it included this bug in following case.
low address ---<-   max order     ->---- high address
               [Node0][Hole][Node0]

Hmm..I'm not sure how many kind of machines will see this bug. But there may be
some.

[kamezawa@...extal linux-2.6.28]$ grep  -R CONFIG_NODES_SPAN arch/*
arch/powerpc/configs/celleb_defconfig:CONFIG_NODES_SPAN_OTHER_NODES=y
arch/powerpc/configs/pseries_defconfig:CONFIG_NODES_SPAN_OTHER_NODES=y
arch/powerpc/configs/cell_defconfig:CONFIG_NODES_SPAN_OTHER_NODES=y
arch/sparc64/defconfig:CONFIG_NODES_SPAN_OTHER_NODES=y
arch/x86/configs/x86_64_defconfig:CONFIG_NODES_SPAN_OTHER_NODES=y

powerpc/sparc64/x86 can see this bug.

IMHO, following 2 arch will be safe because..
On x86-64, it seems it doesn't allows above style of memmap. (BUG_ON() will hit)
Powerpc is originator of this CONFIG_NODES_SPAN_OTHER_NODES and they did test.

Thanks,
-Kame

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