Re: [Xen-users] understanding memory hot-plug in a paravitual domU

[George Shuklin <george.shuklin@xxxxxxxxx>]

AFAIK there is two different operational mode. When we running classic 
old kernels we using just ballooning. And newer kernel (3.1, 3.2) 
supports for memory-hotplug which allow to grow domU memory beyond 
initial memory.
Unfortunately I was not succeed at making memory-hotplug works. Sad.

But some older -xen kernel allow little trick - domain starts with 
'pre-inflated' balloon, allowing (not really, but looking like) grow at 
values higher then initial memory in domU.
On 18.11.2011 15:42, Jordi Moles Blanco wrote:
> Hi,
>
> thanks Kyle for the information.
>
> I had read a lot of documentation and posts in forums and somehow 
> missed that.
> As you say, I feel that people would be less confused with this if 
> mem-max clearly said that you can't grow the balloon higher than the 
> initial memory value.
> Thanks.
>
>
>
> Al 18/11/11 11:47, En/na Kyle Lexmond ha escrit:
> > Hi,
> > Everything that I've read said that you can't balloon the memory
> > beyond the maximum you specified in the config file when you created
> > the domain. (eg.
> > http://www.centos.org/docs/5/html/Virtualization-en-US/virt-task-xm-create-manage-doms.html#id2645186) 
> >
> > So, no, based on the docs, the behaviour that you're seeing is
> > expected, and, no, you can't balloon higher than the initial memory
> > value.
> >
> > Strange that xm mem-max isn't giving errors though.
> >
> > ...
> > > **********
> > > # xm mem-max server 4096
> > > # xm mem-set server 4096
> > > **********
> > >
> > >
> > > can i suppose then that this should work?
> > >
> > > the thing is that xen doesn't complain, but both 'xen top' and the 
> > > machine
> > > itself don't seem to show any increase in the memory.
> > >
> > > However, it works when setting a lower value.
> > >
> > > For example, I can create 'server' with 2048 and then go down to 
> > > 1024 and
> > > then to 2048 again, but never to a higher value. So... i guess that
> > > mem-hotplug works because I can go down and up, but It can never go up
> > > higher than the initial memory value.
> > >
> > > that's why yesterday I was asking if that's is even possible,

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