public void refresh(LocalStatisticsImpl statistics) {
    int flags = statistics.getOsStatFlags();
    if ((flags & PROCESS_STAT_FLAG) != 0) {
      refreshProcess(statistics);
    } else if ((flags & SYSTEM_STAT_FLAG) != 0) {
      refreshSystem(statistics);
    } else {
      throw new RuntimeException(String.format("Unexpected os stats flags %s", flags));
    }
  }
The call should have already checked to make sure usesSystemCalls returns true.
geode-core/src/main/java/org/apache/geode/internal/statistics/OsStatisticsProvider.java