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Re: Only 3.6gb of 64gb RAM recognized by 64bit squeeze



On Tue, May 15, 2012 at 4:30 AM, Henrique de Moraes Holschuh <hmh@debian.org> wrote:
On Mon, 14 May 2012, Stan Hoeppner wrote:
> On 5/13/2012 7:02 PM, Henrique de Moraes Holschuh wrote:
> > On Fri, 11 May 2012, Seyyed Mohtadin Hashemi wrote:
> >> On 5/10/2012 1:16 PM, Stan Hoeppner wrote:
> >>> If this doesn't fix the issue, and memtest and other utils can see all
> >>> 64GB just fine, then I'd say you're dealing with a BIOS bug.
> >>
> >> The very top of /var/log/dmesg has the kernel debug output about the memory
> >> map.  It might well tell us very quickly who is the culprit, if the user
> >> with the problem can post it for the best working case and the non-working
> >> [    0.000000] e820 update range: 00000000e0000000 - 000000101f000000
> >> (usable) ==> (reserved)
> >> [    0.000000] WARNING: BIOS bug: CPU MTRRs don't cover all of memory,
> >> losing 61936MB of RAM.
> >
> > There you have it.
>
> I'm not surprised I was correct WRT a BIOS bug, but I am a little
> embarrassed I didn't know and suggest this would be reported in dmesg.
> I admit I just don't see this very often--this being the 1st time
> actually seeing this WARNING.

Well, it is the first time I've seen a BIOS screw it up so badly as to
have someone lose 61GiB of RAM over it.

> > Any of the latest versions of the longterm kernels (2.6.32, 3.0), or
> > latest 3.2 should be able to repair MTRRs properly, but you have to
> > compile the kernel with that option enabled.  It might be already
> > available, but not enabled by default.  In that case, this might help
> > you:
>
> Yep.  In vanilla 3.2.6 it's selected by default in menuconfig, and you
> can't un-select it.

We _really_ need to have that enabled by default on the Debian kernels
IMO, if we don't enable it already.

--
 "One disk to rule them all, One disk to find them. One disk to bring
 them all and in the darkness grind them. In the Land of Redmond
 where the shadows lie." -- The Silicon Valley Tarot
 Henrique Holschuh

Thank you for the tips Henrique and Stan, unfortunately i don't have time to build/test new kernels this week because i have to finish my thesis. I will have time next week to look at it and report back the results.

best regards,
Mohtadin

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