Lars Rasmusson
2006-Mar-01 16:25 UTC
[Xen-users] Changing Xen hard memory limit in running domain
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 _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users