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Date: Fri, 7 Feb 2014 11:53:57 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
To: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [RFC PATCH 2/3] topology: support node_numa_mem() for determining
 the fallback node
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Cc: Han Pingtian <hanpt@linux.vnet.ibm.com>,
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On Fri, 7 Feb 2014, Joonsoo Kim wrote:

> >
> > It seems like a better approach would be to do this when a node is brought
> > online and determine the fallback node based not on the zonelists as you
> > do here but rather on locality (such as through a SLIT if provided, see
> > node_distance()).
>
> Hmm...
> I guess that zonelist is base on locality. Zonelist is generated using
> node_distance(), so I think that it reflects locality. But, I'm not expert
> on NUMA, so please let me know what I am missing here :)

The next node can be found by going through the zonelist of a node and
checking for available memory. See fallback_alloc().

There is a function node_distance() that determines the relative
performance of a memory access from one to the other node.
The building of the fallback list for every node in build_zonelists()
relies on that.