Re: [Xen-users] Increase Domain 0 memory

[Mark van Dijk <mark@xxxxxxxxxxxxxx>]

Hi,

> For example see this:
> http://fclose.com/b/linux/2258/managing-xen-dom0s-cpu-and-memory/
>
> There's lots of other information recommending to avoid ballooning of 
> dom0 memory. That it is possible, doesn't necessary imply that it's a 
> good thing.

In general, and applicable to the article above, it's indeed wise to
avoid ballooning *down* and/or *automatically*. It's not about avoiding
ballooning at all costs, although this does seem to be the common idea.
I still consider it a wrongful interpretation as there's no objection to
manual ballooning, up or down, for as far as I know. 

In the article I also read:
"Even after booting the system, the VCPU number can be configured by xm
command. We can set Domain-0 have two VCPUs and processor 0 and 1 to be
dedicated to Dom0 by these commands:"

Have you ever tried to do this with dom0_vcpus_pin? Because if my
systems boot with 'dom0_max_vcpus=1 dom0_vcpus_pin' I can't give them
an extra core later on. So either the article is false or my system
refuses things that his system allows.

> I notice performance improvements and "smoothness" in the Xen system, 
> giving dom0 a fixed amount of memory and pinning a couple of cores
> for exclusive use by dom0.

That's my point. Allocating a core for exclusive use by dom0 does not
mean you need to pin them. If I pin the vcpus then I cannot raise/lower
the amount of vcpus. So I am not disagreeing with you that you notice
performance improvements. My whole point there was about (not) having to
pin them.


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