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Subject: Re: [hwloc-devel] Memory affinity
From: Bernd Kallies (kallies_at_[hidden])
Date: 2011-02-28 12:24:44

On Mon, 2011-02-28 at 11:51 -0500, Jeff Squyres wrote:
> Someone just made a fairly disturbing statement to me in an Open MPI bug ticket: if you bind some memory to a particular NUMA node, and that memory later gets paged out, then it loses its memory binding information -- meaning that it can effectively get paged back in at any physical location. Possibly even on a different NUMA node. (he said this in the context of the Linux kernel)
> 1. I have no reason to doubt this person, but was wondering if someone could confirm this (for Linux).

set_mempolicy(2) of recent 2.6 kernels says:
Process policy is not remembered if the page is swapped out. When such a
page is paged back in, it will use the policy of the process or memory
range that is in effect at the time the page is allocated.

> 2. If it is true for Linux, can it also happen on other OSs? Or do other OSs track memory binding information when pages are swapped out?

Dr. Bernd Kallies
Konrad-Zuse-Zentrum für Informationstechnik Berlin
Takustr. 7
14195 Berlin
Tel: +49-30-84185-270
Fax: +49-30-84185-311
e-mail: kallies_at_[hidden]