Xen on RHEL Low Memory Bug

Sometimes when trying to create new Xen domains, my Xen server will refuse to create the domain, complaining with “Error creating domain: Out of memory. xc_dom_boot_mem_init: can’t allocate low memory for domain”.

This problem is a currently known bug, there are various patches and work arounds being discussed on the Red Hat bug tracker. If you don’t want to rebuild Xen with a patch to try and resolve the issue I found that manually reducing the amount of memory that the host (Domain-0) was consuming would resolve the issue.

You can do this by running (as root):

$ xm mem-set Domain-0 1024M

Set to whatever memory value you want, if your host does nothing other than running Xen for all the VMs, you can set it quite low, I recommend 256MB.

This error only seems to happen on x86_64 servers, according to the bug report the reason was “For each vcpu of xen/ia64, it requires 16M contiguous memory for vhpt, but balloon driver didn’t consider this case when it balloons memory.”

For details, refer to bug 466021 at Red Hat.

This entry was posted in Uncategorized and tagged . Bookmark the permalink.