code: void setQuota(String src, long namespaceQuota, long diskspaceQuota)
                                                   throws IOException {
      // sanity check
      if ((namespaceQuota <= 0 && namespaceQuota != FSConstants.QUOTA_DONT_SET &&
           namespaceQuota != FSConstants.QUOTA_RESET) ||
          (diskspaceQuota <= 0 && diskspaceQuota != FSConstants.QUOTA_DONT_SET &&
           diskspaceQuota != FSConstants.QUOTA_RESET)) {
        throw new IllegalArgumentException("Invalid values for quota : " +
                                           namespaceQuota + " and " +
                                           diskspaceQuota);
  
      }
  
      try {
        namenode.setQuota(src, namespaceQuota, diskspaceQuota);
      } catch(RemoteException re) {
        throw re.unwrapRemoteException(AccessControlException.class,
                                       FileNotFoundException.class,
                                       NSQuotaExceededException.class,
                                       DSQuotaExceededException.class);
      }
    }
docs: Sets or resets quotas for a directory.
  @see org.apache.hadoop.hdfs.protocol.ClientProtocol#setQuota(String, long, long)