FastGECToR

1. Introduction

A faster and simpler implementation of GECToR – Grammatical Error Correction: Tag, Not Rewrite with amp and distributed support by deepspeed.

Note: To make it faster and more readable, we remove allennlp dependencies and reconstruct related codes.

2. Requirements

1. Install Pytorch with cuda support pip3 install torch torchvision torchaudio --index-url https://download.pytorch.org/whl/cu118
2. Install NVIDIA-Apex with CUDA and C++ extensions
3. Install the rest packages with pip install -r ./requirements.txt

3. Data Processing

1. Tokenize your data (one sentence per line, split words by space)
2. Generate edits from parallel sents bash scripts/prepare_data.sh
3. (Optional) Define your own target vocab (data/vocabulary/labels.txt)

4. Configuration

• We use deepspeed configs to support distributed training and fp16/bf16 data types. Please refer to the deepspeed config-json for more details.
• We use max_num_tokens to limit the max length of a sequence after tokenization instead of max_len (in word level) as it's not aligned with the length of input_ids and might be misleading.
• --segmented 1 should be used if your input file has spaces between words. If it's set to 0, it will split words by char.

5. Training

• Edit deepspeed_config.json according to your config params. Edit deepspeed_config.json according to your config params. lr, train_batch_size, gradient_accumulation_steps will be inherited from deepspeed config file.

bash scripts/train.sh

* Performance Tuning

• Suppose you want to train a GECToR model with bert-base-uncased (with 110M params), and the max seq len is set to 256 for all cases. There’re some configurations you may need to consider in order to achieve better performance / efficiency.

• The basic config is to use single GPU without any tricks. Then you may get the following statistics.

  global batch size	n_gpus	MaxMemAllocated (CUDA)	GPU Mem Usage (NVIDIA-SMI)
  8	1	3.3GB	5880MiB
  16	1	5.33GB	7610MiB
  32	1	9.28GB	11712MiB
  64	1	17.28GB	20344MiB
  128	1	33.25GB	36654MiB
  256	1	65.21GB	69864MiB

• As you can see, The max batch size you can set is limited by the GPU memory allocation. The simplest way to get a larger batch size is to use gradient accumulation, which accumulates the gradients several steps and update at a given interval. In this case, you can reduce the memory usage a lot.

  global batch size	effective batch size	gradient accumulation steps	n_gpus	MaxMemAllocated (CUDA)	GPU Mem Usage (NVIDIA-SMI)
  256	256	1	1	65.21GB	69864MiB
  256	128	2	1	33.68GB	36654MiB
  256	64	4	1	17.71GB	20152MiB
  256	32	8	1	9.7GB	12344MiB
  256	16	16	1	5.76GB	8018MiB
  256	8	32	1	3.72GB	5872MiB

• Another way to train with a large batch size is to use data parallel strategy, which make model replicas and data batch slices across DP ranks to alleviate the memory consumed per GPU.

  global batch size	n_gpus	MaxMemAllocated (CUDA)	Per GPU Mem Usage (NVIDIA-SMI)
  256	1	65.21GB	69864MiB
  256	2	33.25GB	37038MiB
  256	4	17.28GB	21160MiB
  256	8	9.28GB	12616MiB

• It’s also possible to further reduce the memory usage. For example, you can use FP16 data types for training efficiently at the cost of lower precision. Furthermore, deepspeed’s zero optimizations can also be used alone / together in distributed training. Note that for small models, higher zero stages may not help. For most cases, zero1 (optimizer states partitioning) is enough.

  global batch size	n_gpus	use fp16	use zero1	MaxMemAllocated (CUDA)	Per GPU Mem Usage (NVIDIA-SMI)
  256	1	False	False	65.21GB	69864MiB
  256	1	True	False	35.18GB	38594MiB
  256	8	False	False	9.28GB	12616MiB
  256	8	True	False	5.71GB	9066MiB
  256	8	False	True	8.59GB	12172MiB
  256	8	True	True	4.64GB	7610MiB

• There are other strategies to maximize hardware usage to gain a better performance. Check https://www.deepspeed.ai/ for more details.

6. Inference

• Edit deepspeed_config.json according to your config params

bash scripts/predict.sh

Reference

[1] Omelianchuk, K., Atrasevych, V., Chernodub, A., & Skurzhanskyi, O. (2020). GECToR – Grammatical Error Correction: Tag, Not Rewrite. arXiv:2005.12592 [cs]. http://arxiv.org/abs/2005.12592