RE: [Xen-users] Few Questions / Application of Xen

["M.A. Williamson" <maw48@xxxxxxxxx>]

> I am also somehow new to xen, so somebody correct me if I am wrong.
> But as fas as I understand:
>
> Every domU has it's own kernel which manages it's own memory.
> So every domU also has it's own drive cache.
Yep.

> Most OSs tend to simly use all free memory for drive caches. So does 
> Windows and so does linux. This makes sence for real hardware, since 
> unused free memory is a waste of resources and using every available 
> memory as cache speeds up the mashine extremely. However, if there are 
> other systems that share the same memory, It might be better for one 
> system to have less cache memory and therefor preventing another system 
> from swaping. But to take control of this, every system would need to 
> know about the memory usage of the other systems. That would be totally 
> against system separation.
It depends. If you're (for instance) a hosting company, you might want to 
prevent domains from impacting each other completely. If you run your own 
services in multiple domains, you might want to allow them to grow / shrink 
according to demand, but with limits on how far one domain could grow at 
the expense of others. This is (more or less) something that can be solved 
in the management tools - each domain would report its current load 
statistics and the management tools would reallocate memory between them 
accordingly. You might want an administrator alarm bell so that potential 
resource hogs can be checked out and killed by the sysadmin ;-)
Another thing you'd want to do is share the IO caches between domains - if 
they have a common basic root filesystem, this could be a big win in 
performance and memory utilisation.
Cheers,
Mark

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