Operating system management of large partially allocated objects

This paper describes issues relating to the management of partially allocated objects by persistent object systems. A partially allocated object is one which has not been allocated physical disk space (backing store) for its entire address range. Partially allocated objects can be used to efficiently implement many types of large data structures such as stacks, buffers and sparse arrays. We look at the problem of garbage collecting partially allocated objects and show that to manage such objects correctly, access to the underlying page table information is necessary. Finally we describe the Monads-PC garbage collector which uses the ideas presented in this paper to correctly support partially allocated objects