1. A data processing control method comprising: first assigning, when assigning input data to first Reduce tasks and a second Reduce task that are performed by using a result of Map processes in a MapReduce process, input data with smaller amount than any of amounts of the input data which is assigned to the first Reduce tasks to the second Reduce task; and second assigning the first Reduce tasks and the second Reduce task, to which the input data is assigned, to a server that performs Reduce processes in the MapReduce process such that the second Reduce task is started after the assignment of each of the first Reduce tasks.