DomUs and memory allocation

some questions regarding DomUs and memory.

 

>From the man page for xm at http://linux.die.net/man/1/xm I read that it's not possible to allocate more memory to a DomU than the amount of memory the DomU was booted with:

 

Quote:

 

"vcpu-set domain-id vcpu-count

 

    Enables the vcpu-count virtual CPUs for the domain in question. [b]Like mem-set, this command can only allocate up to the maximum virtual CPU count configured at boot for the domain[/b].

 

    If the vcpu-count is smaller than the current number of active VCPUs, the highest number VCPUs will be hotplug removed. This may be important for pinning purposes.

 

    Attempting to set the VCPUs to a number larger than the initially configured VCPU count is an error. Trying to set VCPUs to < 1 will be quietly ignored.

"

 

I tested this behaviour with a Solaris DomU and it worked; trying to increase the memory behind the limit give the error message

 

# Jul 28 19:31:46 dhcppc5 unix: WARNING: New balloon target (0x19000 pages) is larger than original memory size (0x17000 pages). Ballooning beyond original memory size is not allowed.

 

on the console of the DomU.

 

Is this a permament restriction? Or will it be changed in a future version of Xen?

 

 

Another question:

 

There seems to be no limit in the other direction: I can limit the memory of a DomU to every value I want. And if it's not enough memory for the DomU anymore the DomU  crashes. There's only a lower memory limit for the Dom0 in the SMF properties.

 

So, can I set the minimum memory necessary for a DomU?

 

 

And next:

 

The default value for the mininum memory necessary for the Dom0 is 196 MB. But that's not enough if the Dom0 is running GNOME. This leads to a machine crash if you start to much domains and Xens trys to steal memory from the Dom0 for the DomUs (or if you increase the memory for the Dom0 manually by accident).

 

I think this value should be set dynamically depending on the processes running in the Dom0.