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

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Message-ID: <4AF80AA3.9020400@amd.com>
Date:	Mon, 9 Nov 2009 13:27:15 +0100
From:	Andre Przywara <andre.przywara@....com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Linux-kernel <linux-kernel@...r.kernel.org>
Subject: x86/NUMA: Reason for ignoring too small NUMA nodes?

Hi Andi,

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?
Another comments reads:
      /*
      * Don't confuse VM with a node that doesn't have the
      * minimum amount of memory:
      */
Is that still a valid statement? How can the VM get confused by a node 
with already exhausted memory resources?
(found in arch/x86/mm/{srat,numa}_64.c)

I'd be grateful for some hints!

Thanks,
Andre.

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448 3567 12
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