[libvirt] no check of freeMem before restoring a VM in libxl-driver, is it a bug?

in func 'libxlDomainRestoreFlags',it doesn't use 'libxlFreeMem' to check whether there are enough memory before restoring the vm!It just restore the vm anyway,until xenlight found no enough space in the middle of the process Is this a bug?or It's designed this way by purpose?Thanks in advance.