linux-kernel - Re: [origin tree build failure] Re: [PULL] Please pull hwpoison code for 2.6.32

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Message-ID: <20090926151740.GN30185@one.firstfloor.org>
Date:	Sat, 26 Sep 2009 09:17:34 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>
CC:	torvalds@...ux-foundation.org, fengguang.wu@...el.com,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [origin tree build failure] Re: [PULL] Please pull hwpoison
 code for 2.6.32

Hardware is not the issue, but rather memory hotplug granularity for virtual environments.

Andi Kleen <andi@...stfloor.org> wrote:

>On Sat, Sep 26, 2009 at 04:13:53PM +0200, Ingo Molnar wrote:
>> 
>> >       HWPOISON: Add page flag for poisoned pages
>> 
>> -tip testing found that this change broke 32-bit NUMA builds:
>> 
>>   In file included from include/linux/suspend.h:8,
>>                  from arch/x86/kernel/asm-offsets_32.c:11,
>>                  from arch/x86/kernel/asm-offsets.c:2:
>>   include/linux/mm.h:503:2: error: #error SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > BITS_PER_LONG - NR_PAGEFLAGS
>> 
>> 32-bit NUMA works fine and it was quite useful in finding various bugs 
>> in the past so we dont want to kill it - would be nice to fix this 
>> regression instead. (and preferably not by hacking around this corner of 
>> the Kconfig space)
>
>Thanks for the report. The issue comes from NODES_SHIFT=4
>
>I think I tested the NUMA case, but perhaps not with full NODES_SHIFT.
>
>The easy fix would be to limit NODES_SHIFT to 3 for 32bit (8 nodes max). Do you
>have any problems with that? I doubt there are any >8 nodes NUMAQs left.
>(last time I heard the last machine at IBM was down to < 4)
>
>Another way would be to add a new hash table to move the nodes
>out of the page flags in this case, but that would have more overhead and be
>more complicated.
>
>> btw., this bit in mm/Kconfig:
>> 
>>  config MEMORY_FAILURE
>>         depends on MMU
>>         depends on X86_MCE
>>         bool "Enable recovery from hardware memory errors"
>> 
>> caught my attention. Why is a generic MM facility dependent on an x86 
>> specific config option?
>
>x86 mce is the only code that calls it currently (minus the injector)
>
>It builds on other architectures without trouble and doesn't
>depend on anything x86 specific, but just without a caller it's not very 
>useful, so i made it dependent. I expect other callers in the not too far
>future.
>
>At some point could probably switch over to ARCH_SUPPORTS_MCE_RECOVERY
>or so, but it seemed overkill for the first step.
>
>-Andi
>