Optimized Masked Autoencoders (MAEs)

A lean, optimized implementation of masked autoencoders (MAEs). The skeleton of the code is recycled from Facebook's MAE repository with various simplifications. The following optimizations are implemented:

• [x] FlashAttention-2
• [x] torch.compile
• [x] fused AdamW
• [x] mixed precision training (torch.cuda.amp)
• [x] DDP for distributed training

Dependence of model definitions on the timm library is also removed in this implementation, so the code is self-contained except for the standard libraries. The code was tested with pytorch==2.2.0 and torchvision==0.17.0.

Notes:

• Pretraining (train.py): On a single A100 (with 80 GB GPU memory), it is currently possible to train an MAE with a ViT-H/14 encoder on 1792x1792 images! With 80% masking ratio, you can fit a minibatch size of 8 on a single GPU in this configuration.
• Finetuning (finetune.py): The same model can then be finetuned on a downstream recognition task (again with 1792x1792 images). A single 80GB A100 can fit a batch size of 2 in this setting (this is smaller than in pretraining, because there is no masking in this case).
• The code currently uses DDP for distributed training and it can be scaled up painlessly to multinode training setups without any modifications. See the scripts folder for example distributed training scripts for a SLURM cluster.
• torch.compile yields marginal improvements in my experience (typically around 3-4% improvement in pretraining runtime).