Introduction

This directory contains our pytorch implementation of Transformer-XL. Note that our state-of-the-art results reported in the paper were obtained by training the model on a large-scale TPU cluster, and our pytorch codebase currently does not support distributed training. Here we provide two sets of hyperparameters and scripts:

• *large.sh are for the SoTA setting with large models which might not be directly runnable on a local GPU machine.
• *base.sh are for the base models which can be run on a few GPUs.

The pytorch implementation produces similar results to the TF codebase under the same settings in our preliminary experiments.

Prerequisite

• Pytorch 0.4: conda install pytorch torchvision -c pytorch

Data Prepration

bash getdata.sh

Training and Evaluation

Replicate the "bpc = 1.06" result on enwik8 with a 12-layer Transformer-XL

• Make sure the machine have 4 GPUs, each with at least 11G memory

• Training

  bash run_enwik8_base.sh train --work_dir PATH_TO_WORK_DIR

• Evaluation

  bash run_enwik8_base.sh eval --work_dir PATH_TO_WORK_DIR

Replicate the "PPL = 24.03" result on wikitext-103 with Transformer-XL

• Make sure the machine have 4 GPUs, each with at least 11G memory

• Training

  bash run_wt103_base.sh train --work_dir PATH_TO_WORK_DIR

• Evaluation

  bash run_wt103_base.sh eval --work_dir PATH_TO_WORK_DIR

Other options:

• --batch_chunk: this option allows one to trade speed for memory. For batch_chunk > 1, the program will split each training batch into batch_chunk sub-batches and perform forward and backward on each sub-batch sequentially, with the gradient accumulated and divided by batch_chunk. Hence, the memory usage will propertionally lower while the computation time will inversely higher.
• --div_val: when using adaptive softmax and embedding, the embedding dimension is divided by div_val from bin $i$ to bin $i+1$. This saves both GPU memory and the parameter budget.
• --fp16 and --dynamic-loss-scale: Run in pseudo-fp16 mode (fp16 storage fp32 math) with dynamic loss scaling.
  • Note: to explore the --fp16 option, please make sure the apex package is installed (https://github.com/NVIDIA/apex/).
• To see performance without the recurrence mechanism, simply use mem_len=0 in all your scripts.
• To see performance of a standard Transformer without relative positional encodings or recurrence mechanisms, use attn_type=2 and mem_len=0.

Other datasets:

• Text8 character-level language modeling: check out run_text8_base.sh
• lm1b word-level language modeling: check out run_lm1b_base.sh