linux-kernel - Re: Opteron box and 4Gb memory

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Message-ID: <kjmsl3yuwlz.fsf@pelargir.dolphinics.no>
Date:	Fri, 26 Oct 2007 10:08:08 +0200
From:	Arne Georg Gleditsch <argggh@...phinics.no>
To:	J.A. Magallón <jamagallon@....com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Opteron box and 4Gb memory

"J.A. Magallón" <jamagallon@....com> writes:
> Software Memory Hole
> When "Enabled", allows software memory remapping around the memory
> hole. Options are Enabled and Disabled.
>
> Hardware Memory Hole
> When "Enabled", allows software memory remapping around the memory
> hole. Options are Enabled and Disabled. Note: this is only supported by
> Rev E0 processors and above.
> ( I have two Opteron 275 processors, no idea about revision)

The configuration register used to to reclaim DRAM lost to an MMIO
hole was introduced with revision E of the gen1 Opterons.  (This
feature is supposed to work both in interleaved and non-interleaved
mode.)  What does /proc/cpuinfo say?  (On both?)

(Still, even without this your BIOS should be able to map your memory
so that you are able to use all 4G.  Provided you disable
interleaving, I can't see that there's anything stopping the BIOS from
mapping the memory from node 1 to 0-2G and the memory from node 2 to
4-6G, leaving a 2G hole for MMIO and other junk.  Whether your BIOS
actually supports this is another matter.)

-- 
								Arne.
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