Hi,
I have a machine with 1G RAM, running Xen 3.0.1, and Linux.
I want to create two domU VMs and move ALL the memory, flexibly, back
and
forth between the two VMs.
To do this, I created two domU VMs running Linux, both with kernel boot
parameters mem=1G, to tell Linux to prepare memory tables for 1G RAM.
I booted
the VMs, with xm parameter 'memory=256', i.e. telling Xen to only
give them
256Mb RAM during the startup.
I wanted to later be able to give 700M RAM to one machine and 300M to
the
other, by using the balloon driver ('xm mem-set' command)
Creating and booting the VMs worked fine.
But then I tried to use 'xm mem-set' to give more memory to the VMs,
and that
did *not* work. It's because Xen has set the 'Xen hard memory
limit' (visible
in the VMs' /proc/xen/balloon) to 256M.
I tried to use 'xm mem-max' to change that up to 1G, but 'mem-max'
does not
seem to do anything. Is that correct? Can it be fixed?
There is a bugzilla entry asking for 'mem-max' to be removed, but it
would be
nice to have a way to boot up a domain with less memory than it is
allowed to
have in the future.
http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=212
Is what I'm trying to do perhaps doable in some way, without using
mem-max?
One way that I thought could be an alternative way is this:
I tried to create the VMs one by one, each with 1G of RAM, and
ballooning them
with mem-set down to 256M before saving them. Then I wanted to
restore them, as
they then would have the mem-max paramters and Linux memory tables
set up
correctly.
Sadly, they couldn't be restored, because Xen tries to allocate all
the memory
(= the memory given at the first boot) when it restores the VMs. So
only the
first VM could be restored, even though they only used 256M each.
I mentioned this about a year ago, and got the impression that it was
being
worked on. Was it ever fixed?
"out-of-memory problem when restoring ballooned domains"
http://lists.xensource.com/archives/html/xen-devel/2005-03/msg00480.html
http://lists.xensource.com/archives/html/xen-devel/2005-03/msg00498.html
http://lists.xensource.com/archives/html/xen-devel/2005-03/msg00502.html
Kindly
Lars Rasmusson
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