Re: [Xen-devel] Xen + other stuff?

["Gregory Newby" <newby@xxxxxxxx>]

On Thu, Nov 13, 2003 at 07:24:25PM +0000, Keir Fraser wrote:
> > Bottom line: get enough RAM for each domain (domain0 + virtuals)
> > to share, but the limit will be ~2GB.  When high memory support
> > is added, I understand the limit will be 4GB total (since that's
> > all the domain0 can address).  So, for a new system, 4GB would
> > be the max that Xen can effectively utilize in the immediate future.
> 
> We are unlikely to support more than 4GB total memory on x86. Instead
> we may port Xen to a 64-bit architecture such as Opteron.
> 
> Adding 4GB high-memory support to Linux shouldn't be that hard. Lack
> of this support is why currently you can't give a domain more than
> 800MB. We plan to fix this soon.
> 
> > Or maybe I'm wrong - I'm still trying to learn all this stuff.
> > How, or whether, Xen is able to utilize swap space is not clear
> > to me.  But my advice is to consider everything to operate
> > in "real" mode (i.e., no swap at all) -- it's a good way of
> > having enough memory, even if swapping is available.
> 
> When you specify the memory parameter for a new domain, you are
> specifying a precise allocation of real memory. Xen does not ever swap
> to disc. However, individual guests can feel free to configure their
> own swap file or partition, and performing swapping themselves to/from
> their real memory allocation.

Just to clarify: Do you mean that domain0 can never swap, also?  Or,
are only the virtual domains unable to swap?  My system seems to
*think* that domain0 can swap, using the partitions specified in
/etc/fstab:

$ cat /proc/swaps
Filename                        Type            Size    Used    Priority
/dev/sda3                       partition       1855496 1764    42
/dev/sdb2                       partition       1855496 1768    42

The virtual domains do not have any swap devices allocated.

  -- Greg



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