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This paper provides a comprehensive performance evaluation of job scheduling policies for parallel systems on which large jobs require the maximum or close to the maximum resource available on the system. A wide range of policies are evaluated, including nonpreemptive Backfill policies, time-sharing with Gang Scheduling, and dynamic Equi-spatial policies. Through detailed performance analysis, key problems of each class of policies are identified. As a simpler alternative to Gang Scheduling and Equi-spatial, we propose using a short runtime limit (e.g., one hour as opposed to 10's hours) for Backfill policies. Our simulation results show that applying a short runtime limit on jobs that request a sufficiently large number of processors has the potential to significantly improve FCFS-Backfill policies for all job classes in most workloads studied.