Re: [Xen-devel] Xen - Mosix cluster

["Mark A. Williamson" <mark.williamson@xxxxxxxxxxxx>]

> This may seems a bit of a strange question, but has any thought been given
> to merging the ideas of Xen with Mosix?  A client asked me this, and I
> can't come up with a clear answer.  I understand that both provide
> clustering, but at a different granularity.  A Xen cluster can migrate an
> entire server OS environment, while a Mosix cluster migrates specific
> processes.
>
> I presume there is a basic assumption to Xen usage that the hardware
> resource pool, represented by the resources of any single physical computer
> system, smp or not, is always mayfold greater than the demands of any guest
> domain.  Many OS images running concurently on the same machine is the
> idea.  As a side effect, the resource usage of any on OS environment is
> also limited at a maximum by the limites on any single node machine. (It's
> also limited by configuration, I know.)

All true.  If a node is overloaded, you might migrate some domains off it.

> Would building Xen on top of Mosix allow that resource pool to expand to
> that of the entire Mosix cluster? 

Through Xen migration, you effectively get the resource pool of your entire 
Xen cluster but you can only run processes on their domain's current home 
CPU.

If you were going to use Mosix, it would be *on top* of Xen (not vice-versa) 
and would allow processes to migrate to other domains on other nodes.  Xen 
wouldn't know / care that this was going on, however - it just cares about 
scheduling domains on it's local CPU and doesn't really know about the 
processes within them.

> This would, if feasible, allow not only 
> more domains to be managed by a single Xen kernel, but also allow dynamic
> expansion of single domain images beyond the limits of single hardware
> nodes.

You could theoretically run Mosix in your Xen domains, allowing Mosix to 
migrate processes to other nodes in the cluster.  Xen wouldn't be involved in 
this though.

So, you can run (theoretically - the OpenMosix patches are currently against 
an older Linux kernel) Mosix in XenLinux on top of Xen itself, without 
requiring changes to Xen.  But you can't do this transparently to the guest 
OS.

Btw, somebody was talking about using OpenSSI on top of Xen some time last 
year but I don't know haw they got on.

HTH,
Mark


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