public static OptionalLong getSystemFreeMemoryBytes() {
    return getSystemMemoryBytes().stream()
      .map(value -> value - getMaxMemoryBytes())
      .filter(value -> value > 0)
      .findFirst();
  }
Returns the amount of free memory on this system outside the JVM heap, if available.
planetiler-core/src/main/java/com/onthegomap/planetiler/stats/ProcessInfo.java