[Fedora-xen] Not seeing all RAM

[Daniel P. Berrange]

On Tue, Jul 03, 2007 at 12:27:54AM -0400, Kanwar Ranbir Sandhu wrote:
> Hello,
> 
> I'm running a FC6 dom0, with kernel version,
> kernel-xen-2.6.19-1.2895.fc6 on a Dell PowerEdge 1600SC.  I just
> upgraded it from 1 GB (2 x 512 MB modules) to 3 GB (2 x 1 GB + 2 x 512
> MB).  The BIOS sees all of the ram, but kernel does not.  All I see when
> I run free is this:
> 
>              total       used       free     shared    buffers
> cached
> Mem:       2454528     207876    2246652          0      11032
> 47380
> -/+ buffers/cache:     149464    2305064
> Swap:       524280          0     524280
> 
> It looks like 512 MB is missing.

Let me guest - you are running a 32-bit kernel on the machine ? If so
the problem is likely that the BOIS is remapping a portion of memory
above the 4 GB mark, to make room for PCI device DMA zones. A 32-bit
kernel though can only access physical addrs upto 4 GB, so it can't
see the remapped memory.

> BTW, I appear to be having problems with one of my domUs now too (after
> the ram upgrade).  A PCI device I was handing to the domU is now causing
> the domU kernel to panic, crashing the domU.  I'll try to get a copy of
> the error message.

PCI device mapping to DomUs is insanely fragile, whether it works or not
is mostly luck. In this case since you added more memory, the locaiton of
the PCI device's DMA zone probably changed and by (bad) luck is no longer
accessible to the DomU or something like that.

Dan.
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