A high-performance personal computing environment must avoid perceptible pauses resulting from many page faults within a short period of time. Our performance goals for a paged virtual memory system for the Smalltalk-80 programming environment are both to decrease the average page fault rate and to minimize the pauses caused by clusters of page faults. We have applied program restructuring techniques to the Smalltalk-80 object memory in order to improve the locality of reference. The analysis in this paper considers the clustering of page faults over time and distinguishes between steady-state behavior and phase transitions. We compare the effectiveness of different restructuring strategies in reducing the amount of main memory needed to obtain desired levels of performance.