On management of free space in compressed memory systems

Abstract

This paper considers issues relevant to Operating System control of systems with compressed main memory. The notion of `allocated but unused storage' is introduced. This represents storage which has been recently allocated by the Operating System, but which does not yet occupy physical memory because the lines have not yet been cast out of the cache. We propose that control policies incorporate estimates of allocated but unused storage, as such storage represents a major way in which compressibility can dramatically change. The paper addresses the estimation of allocated but unused storage and analyzes its accuracy on system traces.