[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] RAM allocation and miscellaneous questions

It certainly does Mark (help, that is). I would like to learn more about this 
balloon driver, which could make things very managable. Is there any 
documentation or tutorial-like info about?

Also, though my domains are running happily, I am seeing plenty of 
memory-related errors. I've just hooked up a serial cable between my 
development servers and my desktop (I live with fans) so I'll be able to 
furnish the list with more details.

I have been wondering why my Domain-0 machine hasn't been using swap! :o) So I 
should just dump that partition? I suppose I'll have to be very rigorous when 
it comes to keeping that domain lean yes? (Especially as I only have 4GB to 
play with!). Out side of basic OS functionality, are there any Xen or LVM2 
related processes I have to account for when setting the amount of RAM I can 
use for Domain-0?

I don't suppose I could use the ballon driver for Domain-0 too!?!

Thanks for your reply.


On Wednesday 29 September 2004 03:30 pm, Mark A. Williamson wrote:
> > I'm running 10 VMs now quite happily, using LVM2 with distinct storage
> > areas for each VM filesystem.
> Cool!
> > can I allocate more RAM to each VM than arithmetic would suggest?
> Yes and no ;-)
> Xen does not do paging to disk, so you can't (for instance) tell a domain
> it has 256MB but only give it 128MB and then fake out the extra capacity
> using disk.  The solution under Xen would be to just get the domain to do
> its own paging - this has the same end result and avoids certain
> performance and implementation nasties associated with paging in the VMM.
> Using the balloon driver, you can have a setup where you add and remove
> memory to / from domains according to their need, so that you can shrink
> the memory footprints of domains that don't (currently) need as much in
> core.  This is done manually.
> Of course, you can also use suspend / resume and live migration to move
> domains around in order to balance memory load.
> > Is there some kind of compression or COW
> > that goes on in the Xen memory management code?
> Not right now.  There is a plan to implement a shared buffer cache, which
> would allow domains to share unmodified pages of data that have been read
> from disk.  This is planned as a performance optimisation not a space
> optimisation, however.
> > Would it be best to run one replicated MySQL server (or several with
> > different versions) loaded into a VM on each physical machine, and have
> > all the other machines use that over virtual network connections?
> It probably depends.  I guess you'd save some memory footprint that way
> (compared to running many copies of the servers) but I really don't know
> how much.
> > [64 bit machines]
> > Does Xen work well with Opterons?
> In 32-bit mode, it works.  In 64-bit mode, not quite yet.  x86_64 support
> is under development at the moment and is scheduled as a post-2.0 feature.
> However that will be the preferred path to large memory configurations.
> HTH,
> Mark

This SF.net email is sponsored by: IT Product Guide on ITManagersJournal
Use IT products in your business? Tell us what you think of them. Give us
Your Opinions, Get Free ThinkGeek Gift Certificates! Click to find out more
Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.