Re: [Xen-devel] more than 16 GB in a 32 Bit dom0

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Tue, Feb 08, 2011 at 12:32:19PM +0100, Daniel Bauer wrote:
> From: "Ian Campbell"
>> On Tue, 2011-02-08 at 10:42 +0000, Daniel Bauer wrote:
>>> From: "Keir Fraser"
>>> > On 08/02/2011 07:27, "Daniel Bauer" <mlist@xxxxxxxxxxx> wrote:
>>> >> I've read in many posts, that XEN limits the 32 bit PAE kernel to  
>>> >> 16
>>> >> GB
>>> >> RAM, but I don't find were to enable more. Starting linux without  
>>> >> XEN
>>> >> shows the whole memory. Is there still no solution?
>>> >>
>>> >> I don't have the possibility to upgrade the server to 64 bit.
>>> >
>>> > Then no.
>>>
>>> maybe a silly question, but who sets this limit? IMHO xen, because a
>>> "normal" bigmem kernel accepts upto 64 GB RAM. Is there really no  
>>> switch
>>> to increase the RAM under a 32 bit kernel?
>>
>> The limitation is due to the 32 bit hypervisor, not the kernel.
>
> I know, but I don't find the switch to configure more RAM than 16 GB. I  
> thought that XEN limits it to 16 GB and I could change it and recompile  
> everything.
>
>
>> In my experience a 32 bit (PAE) kernel running on a 64 bit hypervisor
>> works just fine with up to 32GB. In theory up to 160GB is possible in
>> the hypervisor<->PAE-kernel ABI but the kernel tends to run out of
>> lowmem in the 50-60GB range depending on your .config -- this true of
>> native too.
>
> It will be great if I could use 48 GB.
>

Hopefully you have realized having 48 GB of RAM 
on a 32bit Linux (no matter virtualized or not) 
will make it almost unusable? That's because 
you're running out of lowmem.

-- Pasi


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