Effect of batch size on training dynamics by Kevin Shen Mini Distill

The purely formal difference of using the average of the local gradients instead of the sum has favoured the conclusion that using a larger batch size could provide more ‘accurate’ gradient estimates and allow the use of larger learning rates. However, the above analysis shows that, from the perspective of maintaining the expected value of the weight update per unit cost of computation, this may not be true. In fact, using smaller batch sizes allows gradients based on more up-to-date weights to be calculated, which in turn allows the use of higher base learning rates, as each SGD update has lower variance. Both of these factors potentially allow for faster and more robust convergence. In the neural network training, the selection of the minibatch size affects not only the computational cost but also the training performance, as it underlies the loss function. Generally, an approach based on increasing the batch size according to the linear and step functions during the training process is known to be effective in improving the generalization performance of a network.

Effect of batch size on training dynamics

On top of the model architecture and the number of parameters, the batch size is the most effective hyperparameter to control the amount of GPU memory an experiment uses. The proper method to find the optimal batch size that can fully utilize the accelerator is via GPU profiling, a process to monitor processes on the computing device. Both TensorFlow and PyTorch provide detailed guides and tutorials on how to perform profiling in their framework.

Adaptive subgradient methods for online learning and stochastic optimization

Finally, here are some articles and papers on the topic of batch size and its effects on deep neural networks. We trained 6 different models, each with a different batch size of 32, 64, 128, 256, 512, and 1024 samples, keeping all other hyperparameters same in all the models. We see that Batch Sizes are extremely important in the model training process. This is why in most cases, you will see models trained with different batch sizes.

As also pointed out in Wilson & Martinez (2003) and Goyal et al. (2017). It is important to note that (9) is a better approximation if the batch size and/or the base learning rate are small. In this paper, we review common assumptions on learning rate scaling and training duration, as a basis for an experimental comparison of test performance for different mini-batch sizes. This section presents numerical results for the training performance of convolutional neural network architectures for a range of batch sizes m and base learning rates ~η. Jastrzebski et al. (2017) claim that both the SGD generalization performance and training dynamics are controlled by a noise factor given by the ratio between the learning rate and the batch size, which corresponds to linearly scaling the learning rate.

On large-batch training for deep learning: generalization gap and sharp minima

However, it is well known that too large of a batch size will lead to poor generalization (although currently it’s not known why this is so). For convex functions that we are trying to optimize, there is an inherent tug-of-war between the benefits of smaller and bigger batch sizes. On the one extreme, using a batch equal to the entire dataset guarantees convergence to the global optima of the objective function. However, this is at the cost of slower, empirical convergence to that optima. On the other hand, using smaller batch sizes have been empirically shown to have faster convergence to “good” solutions.

How does batch size affect training loss?

higher batch sizes leads to lower asymptotic test accuracy. we can recover the lost test accuracy from a larger batch size by increasing the learning rate.

Overall, the experimental results support the broad conclusion that using small batch sizes for training provides benefits both in terms of range of learning rates that provide stable convergence and achieved test performance for a given number of epochs. The reported experiments have explored the training dynamics and generalization performance of small batch training for different datasets and neural networks. In the SGD weight update formulation (5), the learning rate ~η corresponds to the base learning rate that would be obtained from a linear increase of the learning rate η of (2), (3) with the batch size m, i.e. To investigate these issues, we have performed a comprehensive set of experiments for a range of network architectures. Some works in the optimization literature have shown that increasing the learning rate can compensate for larger batch sizes. With this in mind, we ramp up the learning rate for our model to see if we can recover the asymptotic test accuracy we lost by increasing the batch size.

Entropy guided adversarial model for weakly supervised object localization

We’re justified in scaling mean and standard deviation of the gradient norm because doing so is equivalent to scaling the learning rate up for the experiment with smaller batch sizes. Essentially we want to know “for the same distance moved away from the initial weights, what is the variance in gradient norms for different batch sizes”? Keep in mind we’re measuring the variance in the gradient norms and not variance in Effect of batch size on training dynamics the gradients themselves, which is a much finer metric. This implies that, when increasing the batch size, a linear increase of the learning rate η with the batch size m is required to keep the mean SGD weight update per training example constant. In experiments, we aim to investigate in detail the effectiveness of the proposed method by analyzing the transition for the value of loss function and prediction accuracy.

  • You then increase the value if the model is underutilizing the GPU memory, and repeat the process until you hit the memory capacity.
  • Batch size is one of the important hyperparameters to tune in modern deep learning systems.
  • If you want a breakdown of this paper, let me know in the comments/texts.
  • Following the procedure of Goyal et al. (2017), the implementation of the gradual warm-up corresponds to the use of an initial learning rate of η/32, with a linear increase from η/32 to η over the first 5% of training.
  • Larger batch sizes has many more large gradient values (about 10⁵ for batch size 1024) than smaller batch sizes (about 10² for batch size 2).

Instead what we find is that larger batch sizes make larger gradient steps than smaller batch sizes for the same number of samples seen. Note that the Euclidean norm can be interpreted as the Euclidean distance between the new set of weights and starting set of weights. Therefore, training with large batch sizes tends to move further away from the starting weights after seeing a fixed number of samples than training with smaller batch sizes. In other words, the relationship between batch size and the squared gradient norm is linear.

The results presented in Figure 14 show that the performance with BN generally improves by reducing the overall batch size for the SGD weight updates. The collected data supports the conclusion that the possibility of achieving the best test performance depends on the use of a small batch size for the overall SGD optimization. This implies that, adopting the linear scaling rule, an increase in the batch size would also result in a linear increase in the covariance matrix of the weight update ηΔθ.

  • From the plots, we observe similar convergence for some of the curves corresponding to the same value of ~η with batch sizes in the range 4≤m≤64, but with degraded training performance for larger batch sizes.
  • However, keep in mind that PyTorch/TensorFlow or other processes might request more GPU memory in the middle of an experiment and you risk OOM, I hence prefer having some wiggle room.
  • We will investigate batch size in the context of image classification.
  • Where the bars represent normalized values and i denotes a certain batch size.
  • There’s an excellent discussion of the trade offs of large and small batch sizes here.
  • Running the example creates a figure with eight line plots showing the classification accuracy on the train and test sets of models with different batch sizes when using mini-batch gradient descent.

This is intuitively explained by the fact that smaller batch sizes allow the model to “start learning before having to see all the data.” The downside of using a smaller batch size is that the model is not guaranteed to converge to the global optima. It will bounce around the global optima, staying outside some ϵ-ball of the optima where ϵ depends on the ratio of the batch size to the dataset size. The orange and purple curves are for reference and are copied from the previous set of figures. Like the purple curve, the blue curve trains with a large batch size of 1024.

Because neural network systems are extremely prone overfitting, the idea is that seeing many small batch size, each batch being a “noisy” representation of the entire dataset, will cause a sort of “tug-and-pull” dynamic. This “tug-and-pull” dynamic prevents the neural network from overfitting on the training set and hence performing badly on the test set. Smith et al. (2017) have recently suggested using the linear scaling rule to increase the batch size instead of decreasing the learning rate during training. It may however be approximately applicable in the last part of the convergence trajectory, after having reached the region corresponding to the final minimum. Finally, it is worth noting that in practice increasing the batch size during training is more difficult than decreasing the learning rate, since it may require, for example, modifying the computation graph.

However, it requires specifying the way of increasing the batch size beforehand. In this study, we propose a more flexible method that implies temporarily varying a small batch size to destabilize the loss function when a change in the training loss satisfies the predefined stopping criterion. Repeating the destabilization step allows a parameter to avoid being trapped at the local minima and to converge at a robust minimum, thereby improving generalization performance.