protected void putbackBuffer(ByteBuffer buf) {
    if (buf.capacity() != bufSize || (reservoirEnabled ^ buf.isDirect())) {
      LOG.warn("Trying to put a buffer, not created by this pool! Will be just ignored");
      return;
    }
    buffers.offer(buf);
  }
Return back a ByteBuffer after its use. Don't read/write the ByteBuffer after the returning.
@param buf ByteBuffer to return.
hbase-common/src/main/java/org/apache/hadoop/hbase/io/ByteBuffAllocator.java