php上载：Fatal error: Allowed memory size of

    function download($filepath, $filename = '') {
        if(!$filename) $filename = basename($filepath);
        if(is_ie()) $filename = rawurlencode($filename);
        $filetype = fileext($filename);
        $filesize = sprintf("%u", filesize($filepath));
        if(ob_get_length() !== false) @ob_end_clean();
        header('Pragma: public');
        header('Last-Modified: '.gmdate('D, d M Y H:i:s') . ' GMT');
        header('Cache-Control: no-store, no-cache, must-revalidate');
        header('Cache-Control: pre-check=0, post-check=0, max-age=0');
        header('Content-Transfer-Encoding: binary');
        header('Content-Encoding: none');
        header('Content-type: '.$filetype);
        header('Content-Disposition: attachment; filename="'.$filename.'"');
        header('Content-length: '.$filesize);
        readfile($filepath);
        exit;
    }

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 750743553 bytes) in /var/www/nms/framebase/libs/functions/extention.func.php on line 233