code: public static long getMultipartSizeProperty(Configuration conf,
        String property, long defVal) {
      long partSize = conf.getLongBytes(property, defVal);
      if (partSize < MULTIPART_MIN_SIZE) {
        LOG.warn("{} must be at least 5 MB; configured value is {}", property, partSize);
        partSize = MULTIPART_MIN_SIZE;
      }
      return partSize;
    }
docs: Get a size property from the configuration: this property must be at least
  equal to {@link COSConstants#MULTIPART_MIN_SIZE}. If it is too small, it is
  rounded up to that minimum, and a warning printed.
  
  @param conf configuration
  @param property property name
  @param defVal default value
  @return the value, guaranteed to be above the minimum size