AVM: application-level virtual memory

Virtual memory (VM) is a notoriously complicated abstraction to implement, and is hard to change, specialize, or replace. Although a certain degree of flexibility is achieved by user-level pagers, the control they provide is limited: they leave much of the VM system fixed in the kernel, unreachable by the application. As applications become more diverse and the opportunity cost of bad memory policies grows, it is essential for applications to have more control over the VM abstraction. We motivate and describe a VM system that is implemented completely at the application level. To the best of our knowledge this system is the first complete example of application-level virtual memory (AVM). AVM allows applications to easily specialize, modify, or even replace the VM abstractions offered. For example, on architectures with software TLB management, applications can even select their own page-table structures. In addition, AVM simplifies the OS kernel, since the kernel only multiplexes and does not abstract physical memory. A prototype AVM system is implemented for Aegis, an experimental exokernel.