Re: Migrate/Save of 32-bit domU Broken on Xen 3.1.2 64-bit dom0

[Joshua West <jwest@brandeis.edu>]

Joshua West wrote:
> Hi Dan,
>
> Dan Magenheimer wrote:
>> Joshua --
>>
>> Why do you need so much memory on dom0?  Are you thinking
>> that the total memory available to guests is limited to
>> what dom0 has?  Or are you running some memory-hungry
>> applications on dom0?
>>   
>
> Hmm, I thought that a 32-bit dom0 system can only have up to 16GB of 
> memory available to it and its domU's -- and a 64-bit dom0 can have a 
> max of 32GB.  I only allocate ~512MB of memory to the dom0's 
> themselves.  "xm info" shows us the rest of whats available for use by 
> domU's.
>
> Thus, even if I have 32GB of RAM in a server, the total memory that 
> will be used in dom0 + all domU's can only add up to 16GB.  Am I just 
> plain old wrong?
>
>> Note that 64-bit Xen + 32-bit Dom0 will support both 32-bit
>> and 64-bit domU's. (Oracle VM uses this configuration by
>> default on 64-bit capable machines.)  And save/restore/migration
>> has been tested to work for this (with the patch Kurt posted).
>>   
>
> Interesting.  For some reason I thought that the Hypervisor had to 
> match the dom0's kernel.  So you're saying that if I compile the Xen 
> Hypervisor as 64-bit and my dom0 + domU's both as 32-bit, I can reach 
> the full capacity of my servers with respect to RAM (32GB) instead of 
> being limited to 16GB?  (And this only works with Kurt's patches?).

Sorry about this second question.  Looks like you already answered it in 
your first message :-/  I'm going to give it a whirl (64-bit Xen 
Hypervisor, 32-bit dom0, 64-bit and 32-bit domU's -- all with Kurt's 
patches).  Thanks.

>
>> Dan  
>
>


-- 
Joshua West
Systems Engineer
Brandeis University
http://www.brandeis.edu