linux-kernel - Re: [PATCH 1/1] mm: Inconsistent use of node IDs

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Message-Id: <200703130019.30953.ak@suse.de>
Date:	Tue, 13 Mar 2007 00:19:30 +0100
From:	Andi Kleen <ak@...e.de>
To:	Ethan Solomita <solo@...gle.com>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/1] mm: Inconsistent use of node IDs

On Monday 12 March 2007 23:51, Ethan Solomita wrote:
> This patch corrects inconsistent use of node numbers (variously "nid" or
> "node") in the presence of fake NUMA.

I think it's very consistent -- your patch would make it inconsistent though.

> Both AMD and Intel x86_64 discovery code will determine a CPU's physical
> node and use that node when calling numa_add_cpu() to associate that CPU
> with the node, but numa_add_cpu() treats the node argument as a fake
> node. This physical node may not exist within the fake nodespace, and
> even if it does, it will likely incorrectly associate a CPU with a fake
> memory node that may not share the same underlying physical NUMA node.
> 
> Similarly, the PCI code which determines the node of the PCI bus saves
> it in the pci_sysdata structure. This node then propagates down to other
> buses and devices which hang off the PCI bus, and is used to specify a
> node when allocating memory. The purpose is to provide NUMA locality,
> but the node is a physical node, and the memory allocation code expects
> a fake node argument.

Sorry, but when you ask for NUMA emulation you will get it. I don't see
any point in a "half way only for some subsystems I like" NUMA emulation. 
It's unlikely that your ideas of where it is useful and where is not
matches other NUMA emulation user's ideas too.

Besides adding such a secondary node space would be likely a huge long term 
mainteance issue. I just can it see breaking with every non trivial change.

NACK.

-Andi
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