CentOS 5.4 x86_64 only detects 32GB RAM while Fedora x86_64 correctly lists 128GB
 

Diederick Stoffers wrote:
> Hi,
>
> We have a new 24-core Dell PowerEdge R905 server with 128GB's RAM. The
> 64 bits version of Fedora 12 lists the correct amount of 128GB, CentOS
> only finds 32GB (and so does Scientific Linux). I would much prefer to
> use CentOS (most of the software we use is specifically designed for
> CentOS). Does anyone know what is causing this/how to fix it?
>
> Many Thanks,
>
> Diederick
>
Hi

Very strange. I have a Dell Precision T7500 with 48GB of memory and
CentOS-5.4 finds everything:
kalyke (Linux)$ uname -rm; free
2.6.18-164.6.1.el5 x86_64
total used free shared buffers cached
Mem: 49453972 48273592 1180380 0 219116 41775056
-/+ buffers/cache: 6279420 43174552
Swap: 50331604 0 50331604
kalyke (Linux)$

Regards

mg.

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CentOS 5.4 x86_64 only detects 32GB RAM while Fedora x86_64 correctly lists 128GB
 

On 12/7/2009 7:24 AM, Diederick Stoffers wrote:
> [root@localhost ~]# uname -a
> Linux localhost.localdomain 2.6.18-164.6.1.el5xen #1 SMP Tue Nov 3
> 16:48:13 EST 2009 x86_64 x86_64 x86_64 GNU/Linux
>

If you dig back through the xen-users mailing list, there's a thread
that discusses this recently. Look for a subject of "[Xen-users] Memory
not seen in Dom0" back around Nov 8th. I tried to get GMane's web
interface to toss up a direct link to the thread, but gave up.

nntp://news.gmane.org/gmane.comp.emulators.xen.user

Supposedly, it's not an issue unless you really really want >32GB in the
Dom0 host. The Xen 64bit kernel (currently?) limits the Dom0 to 32GB.
But any guest VMs that you create will initially use the RAM not used by
the Dom0.

Most folks recommend that you limit Dom0's memory usage in grub.conf
(using the dom0_mem= argument). Or you can set it later using "xm
mem-set 0 ###M".

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