linux-kernel - Re: x86/NUMA: Reason for ignoring too small NUMA nodes?

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Message-ID: <20091109123824.GE26740@basil.fritz.box>
Date:	Mon, 9 Nov 2009 13:38:24 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Andre Przywara <andre.przywara@....com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: x86/NUMA: Reason for ignoring too small NUMA nodes?

On Mon, Nov 09, 2009 at 01:27:15PM +0100, Andre Przywara wrote:
> while experimenting with a system with a memory-less NUMA node I stumbled 
> upon code in the Linux kernel which ignores nodes containing less than a 
> certain amount of RAM, obviously to fix systems with a buggy BIOS.
> Can you elaborate on this? What kind of incorrect entry have you seen?
> To correctly map the memory less node I did a patch to accept at least 
> nodes with exactly zero bytes of memory (read: no SRAT memory entry), was 
> this special condition also present in the buggy machines?

It was a misparsed numa node, not zero. I don't remember if 
the bug was in Linux or in the BIOS. This was a sanity check
to catch all such cases. I haven't seen misparsed nodes for quite some 
time, so in theory it could be removed I guess.

Zero size node were back then not supported in the VM. I still think
the concept doesn't make too much sense: a memory range without
memory (and it bitrots all the time even today, see recent patches)

-Andi

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