code: private boolean incSlotLimit(JobInfo info, TaskType type, LimitType limit) {
      switch (limit) {
        case MIN:
          if (type == TaskType.MAP) {
            if (info.minMaps < runnableTasks(info, type)) {
              info.minMaps += 1;
              return true;
            }
          } else {
            if (info.minReduces < runnableTasks(info, type)) {
              info.minReduces += 1;
              return true;
            }
          }
          return false;
        case MAX:
          if (type == TaskType.MAP) {
            if (info.maxMaps < runnableTasks(info, type)) {
              info.maxMaps += 1;
              return true;
            }
          } else {
            if (info.maxReduces < runnableTasks(info, type)) {
              info.maxReduces += 1;
              return true;
            }
          }
          return false;
      }
      // Never come here
      return false;
    }
docs: Increment the slot limit of a job
  @param info The JobInfo of the job
  @param type Map or Reduce
  @param limit Max or Min
  @return true if we can increment