When a virtual machine (VM) runs in the background in an idle state, its memory remains allocated and is unavailable for other host processes or other VMs on the host. This disclosure describes hypervisor-aware virtio ballooning in dynamic host-guest memory allocation. Per the techniques, memory can be dynamically transferred between the guest virtual machines and their host. The inflation operation that enables dynamic transfer of guest VM memory to the host notifies the hypervisor of pages to be freed and also requests the host kernel to free those pages. The techniques can function even in operating systems that lack a way for a hypervisor to subscribe to notifications of page addition or removal events.
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Saini, Udam; Hoyle, Michael; and Gold, Noah, "Dynamic Memory Allocation for a Guest Virtual Machine", Technical Disclosure Commons, (January 20, 2022)