A study of large object spaces

Abstract

This paper examines the design space for copying garbage collectors (GCs) in which "large objects" are managed in a separate, non-copy-collected space. We focus on two main issues: 1. how to set the policy for classifying objects as "large" 2. how to manage the large object space We explore these issues experimentally using the Oscar GC testbed. In particular, we vary the threshold size of large objects and also whether the objects may contain pointers. Furthermore, we compare the performance of treadmill collection to that of mark-and-sweep collection for managing the large object space. We find that for some heaps there is a minimum cutoff size below which adding objects to the large object space does not result in a performance improvement, while for others no such cutoff exists. In general, including pointer-containing objects in the large object space seems beneficial. Finally, the exact method used to collect the large object space does not significantly influence overall performance.