A Localized Tracing Scheme Applied to Garbage Collection

We present a method to visit all nodes in a forest of data structures while taking into account object placement. We call the technique a Localized Tracing Scheme as it improves locality of reference during object tracing activity. The method organizes the heap into regions and uses trace queues to defer and group tracing of remote objects. The principle of localized tracing reduces memory traffic and can be used as an optimization to improve performance at several levels of the memory hierarchy. The method is applicable to a wide range of uniprocessor garbage collection algorithms as well as to shared memory multiprocessor collectors. Experiments with a mark-and-sweep collector show performance improvements up to 75% at the virtual memory level.