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

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.


Joshua West
Systems Engineer
Brandeis University

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