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

To: Joshua West <jwest@xxxxxxxxxxxx>, "dan.magenheimer@xxxxxxxxxx" <dan.magenheimer@xxxxxxxxxx>
Subject: Re: [Xen-devel] Migrate/Save of 32-bit domU Broken on Xen 3.1.2 64-bit dom0
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Sat, 19 Jan 2008 08:04:40 +0000
Cc: Kurt Hackel <kurt.hackel@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On 18/1/08 23:29, "Joshua West" <jwest@xxxxxxxxxxxx> wrote:

> 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?).

As long as you run 64-bit Xen you can run 32-bit dom0 and domUs and use the
full memory of your system. The 32-bit guests are not even limited to 16GB
each, let alone jointly. This is true even without Kurt's patches. What
Kurt's patches fix is save/restore/migrate of a 64-bit domU from a 32-bit
dom0.

 -- Keir



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