module.freeze_bn()

As an AI language model, I do not have sufficient context to determine what module is being referred to in this code snippet. However, assuming that the module refers to a deep learning framework or library, the function freeze_bn() might be used to freeze the batch normalization layers during training. This can be useful in certain scenarios where the batch normalization parameters are already well-trained and should not be updated further to prevent overfitting. By freezing the batch normalization layers, the training process can focus on updating the other parameters of the model.