Sequence packing
# 🚀 Feature request

Add sequence packing support

## Motivation

Faster training, higher utilization, replicate experiments. 
See https://github.com/google-research/text-to-text-transfer-transformer/issues/365

## Your contribution

I think it makes sense doing something similar to other frameworks which already have this implemented (e.g https://github.com/tensorflow/mesh/blob/6a812c8bb847e081e976533ed497c7c5016bb1ec/mesh_tensorflow/transformer/dataset.py#L474-L504 )
This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
