linux-kernel - Re: [PATCH x86/mm UPDATED] x86-64, NUMA: Fix distance table handling

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Date:	Wed, 2 Mar 2011 06:30:59 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Tejun Heo <tj@...nel.org>
cc:	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	tglx@...utronix.de, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH x86/mm UPDATED] x86-64, NUMA: Fix distance table
 handling

On Wed, 2 Mar 2011, Tejun Heo wrote:

> From d968be2ff381c667bfd09795f82248558902a1ae Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@...nel.org>
> Date: Wed, 2 Mar 2011 11:22:14 +0100
> 
> NUMA distance table handling has the following problems.
> 
> * numa_reset_distance() uses numa_distance * sizeof(numa_distance[0])
>   as the table size when it should be using the square of
>   numa_distance.
> 
> * The same size miscalculation when allocation space for phys_dist in
>   numa_emulation().
> 
> * In numa_emulation(), phys_dist must be reserved; otherwise, the new
>   emulated distance table may overlap it.
> 
> Fix them and, while at it, take numa_distance_cnt resetting in
> numa_reset_distance() out of the if block to simplify the code a bit.
> 
> David Rientjes reported incorrect handling of distance table during
> emulation and Yinghai identified the above problems and wrote the
> original patch to fix the problems.  This patch is based on Yinghai's
> patch.
> 
> -v2: Ingo was unhappy with 80-column limit induced linebreaks.  Let
>      lines run over 80-column.
> 
> Reported-by: David Rientjes <rientjes@...gle.com>
> Patch-originally-from: Yinghai Lu <yinghai@...nel.org>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Ingo Molnar <mingo@...e.hu>

Acked-by: David Rientjes <rientjes@...gle.com>

There's also this in numa_emulation() that isn't a safe assumption:

        /* make sure all emulated nodes are mapped to a physical node */
        for (i = 0; i < ARRAY_SIZE(emu_nid_to_phys); i++)
                if (emu_nid_to_phys[i] == NUMA_NO_NODE)
                        emu_nid_to_phys[i] = 0;

Node id 0 is not always online depending on how you setup your SRAT.  I'm 
not sure why emu_nid_to_phys[] would ever map a fake node id that doesn't 
exist to a physical node id rather than NUMA_NO_NODE, so I think it can 
just be removed.  Otherwise, it should be mapped to a physical node id 
that is known to be online.
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