[Keras] 使用多 gpu 并行训练并使用 ModelCheckpoint() 可能遇到的问题

问题描述

在使用 callbacks.ModelCheckpoint() 并进行多 gpu 并行计算时，callbacks 函数会报错：

TypeError: can't pickle ...(different text at different situation) objects

这个错误形式其实跟使用多 gpu 训练时保存模型不当造成的错误比较相似：

To save the multi-gpu model, use .save(fname) or .save_weights(fname)
with the template model (the argument you passed to multi_gpu_model),
rather than the model returned by multi_gpu_model.

这个问题在我之前的文章中也有提到：[Keras] 使用Keras调用多GPU，并保存模型
。显然，在使用检查点时，默认还是使用了 paralleled_model.save() ，进而导致错误。为了解决这个问题，我们需要自己定义一个召回函数。

解决方法

法一

original_model = ...
parallel_model = multi_gpu_model(original_model, gpus=n)

class MyCbk(keras.callbacks.Callback):

    def __init__(self, model):
         self.model_to_save = model

    def on_epoch_end(self, epoch, logs=None):
        self.model_to_save.save('model_at_epoch_%d.h5' % epoch)

cbk = MyCbk(original_model)
parallel_model.fit(..., callbacks=[cbk])

---

法二

class ParallelModelCheckpoint(ModelCheckpoint):
    def __init__(self,model,filepath, monitor='val_loss', verbose=0,
                 save_best_only=False, save_weights_only=False,
                 mode='auto', period=1):
        self.single_model = model
        super(ParallelModelCheckpoint,self).__init__(filepath, monitor, verbose,save_best_only, save_weights_only,mode, period)

    def set_model(self, model):
        super(ParallelModelCheckpoint,self).set_model(self.single_model)

check_point = ParallelModelCheckpoint(single_model ,'best.hd5')

---

法三

class CustomModelCheckpoint(keras.callbacks.Callback):

    def __init__(self, model, path):
        self.model = model
        self.path = path
        self.best_loss = np.inf

    def on_epoch_end(self, epoch, logs=None):
        val_loss = logs['val_loss']
        if val_loss < self.best_loss:
            print("\nValidation loss decreased from {} to {}, saving model".format(self.best_loss, val_loss))
            self.model.save_weights(self.path, overwrite=True)
            self.best_loss = val_loss

model.fit(X_train, y_train,
              batch_size=batch_size*G, epochs=nb_epoch, verbose=0, shuffle=True,
              validation_data=(X_valid, y_valid),
              callbacks=[CustomModelCheckpoint(model, '/path/to/save/model.h5')])

参考资料

• Multi_gpu in keras not working with callbacks, but works fine if callback is removed #8649
• call_back_error when using multi_gpu_model #10218
• Keras同时用多张显卡训练网络
• ModelCheckpoint callback with multi_gpu fails to save the model, throws error after 1st epoch #8764