请问一下，对于ByteBuffer makeSpace函数会经常把数据往前移动，也就是说拷贝，这个会比较费吗？

[asynchronous]

上图中的

 void makeSpace(size_t len)
        {
            //kCheapPrepend为保留的空间
            if (writableBytes() + prependableBytes() < len + kCheapPrepend)
            {
                // FIXME: move readable data
                m_buffer.resize(m_writerIndex + len);
            }
            else
            {
                // move readable data to the front, make space inside buffer
                //assert(kCheapPrepend < readerIndex_);
                if (kCheapPrepend >= m_readerIndex)
                    return;

                size_t readable = readableBytes();
                std::copy(begin() + m_readerIndex,
                    begin() + m_writerIndex,
                    begin() + kCheapPrepend);
                m_readerIndex = kCheapPrepend;
                m_writerIndex = m_readerIndex + readable;
            }
        }

应该在收包的过程中，这种copy数据应该是很常发生的