[libvirt-users] start a domain, minimal memory request.

Hi: I use libvirt manage virtual guest, When I start many virtual domain(my host 128G physical memory）, example, I start 100 guest, 1G per guest。sometime I will encounter "cannot allocate memory", "cannot set up guest memory \'pc.ram\'： cannot allocate memory". sometime encounter qemu process killed by system(oom), I want to know what minimal memory need when start a domain ? and how many host free memory reserve can ensure vm running steady. Thanks