Method and system for memory oversubscription for virtual machines
A method for oversubscribing a host memory of a host running a virtual machine monitor (VMM), comprising, examining a virtual machine (VM) memory for a VM for metadata associated with the VM memory, the metadata maintained by a guest OS running on the VM, collecting the metadata for the VM memory, and managing the VM memory using the metadata for oversubscribing a host memory.
1. A method for oversubscribing a host memory of a host running a virtual machine monitor (VMM), comprising:
examining a virtual machine (VM) memory for the VM for metadata associated with the VM memory, the metadata including information from a physical frame number (PFN) database extracted from a kernel of the guest OS, the PFN database maintaining state information for each PFN the guest OS the VM knows about;
collecting the metadata for the VM memory; and
managing the VM memory using the metadata for oversubscribing a host memory.
2. The method of claim 1 , wherein the step of managing comprises:
selecting a portion of the VM memory for removal based on the metadata for the portion of the VM memory; and
removing the portion of the VM memory from the VM.
3. The method of claim 1 , wherein the step of managing comprises:
selecting one or more memory pages of the VM memory for removal based on the metadata for the one or more memory pages; and
removing the selected memory pages from the VM.
4. The method of claim 3 , wherein the selecting for removal is based on the metadata indicating the memory page is free or zero.
5. The method of claim 2 , wherein the memory where the metadata is non-pageable is not selected for removal.
6. The method of claim 1 , wherein the metadata for the memory is one of: free, zero, or non-pageable.
7. The method of claim 6 , wherein the step of collecting comprises:
inspecting the physical frame number (PFN) database for the free or zero metadata for the memory.
8. The method of claim 5 , wherein the step of collecting comprises:
searching kernel virtual address ranges for the memory with the non-pageable metadata.
9. The method of claim 7 , wherein the step of collecting further comprises:
searching kernel virtual address ranges for the memory with the non-pageable metadata.
10. The method of claim 1 , wherein the steps are performed by the virtual machine monitor (VMM).
11. The method of claim 1 , wherein the memory, the VM, and the guest OS are manipulated without the intervention by the guest OS.
12. A method for managing a host memory of a host by a virtual machine monitor (VMM), comprising:
introspecting a physical frame number (PFN) database of a virtual machine (VM) memory for a VM for metadata associated with the VM memory, the metadata maintained by a guest OS running on the VM, the metadata indicating whether a given frame is used and whether the given frame belongs to special regions that should not be removed or unmapped; and
oversubscribing the host memory by using the metadata.
13. The method of claim 12 , wherein the step of oversubscribing comprises:
selecting a portion of the VM memory for removal based on the metadata for the portion of the VM memory;
removing the portion of the VM memory from the VM.
14. The method of claim 13 , wherein the selecting for removal is based on the metadata indicating the memory is free or zero.
15. The method of claim 13 , wherein the memory that belongs to non-pageable kernel virtual address regions is not selected for removal.
16. The method of claim 12 , wherein the metadata for the memory or the memory page is one of: free, zero, or non-pageable.
17. The method of claim 16 , wherein the step of introspecting comprises:
inspecting the PFN database for the free or zero metadata for the memory.
18. The method of claim 12 , wherein the step of oversubscribing comprises:
selecting one or more memory pages of the VM memory for removal based on the metadata for the one or more memory pages;
removing the selected memory pages from the VM.
19. The method of claim 12 , wherein the memory, the VM, and the guest OS are manipulated without the knowledge of the VM and the guest OS.
20. A system for oversubscribing a host memory of a host running a virtual machine monitor (VMM), comprising:
a virtual machine (VM) memory on a VM, the VM running in the host memory;
a metadata database with metadata associated with the VM memory, the metadata maintained by a guest OS, the metadata including information from a physical frame number (PFN) database extracted from a kernel of the guest OS, the PFN database maintaining state information for each PFN the guest OS the VM knows about;
wherein, the VMM manages the VM memory using the metadata for oversubscribing a host memory.