A first hypervisor uses a first version of a virtual-memory file system (VMemFS) suspends virtual machines. A second hypervisor uses a instance of the VMemFS, the version of which may be the same or different from the first version. The VMemFS is designed so that an instance of the same or a later version of the VMemFS can read and ingest information in memory written to memory by another instance of the VMemFS. Accordingly, the second hypervisor resumes the virtual machines, effecting an update or other swap of hypervisors with minimal interruption. In other examples, the swapped hypervisors support process containers or simply support virtual memory.