text: Title: train meachine translation  OOM 
  Body: ### Description
  ![屏幕快照 2021-04-22 上午10 18 34](https://user-images.githubusercontent.com/33311822/115646780-5f383980-a355-11eb-93f0-f8438d825f55.png)
  
  Can you tell me why even I set batch_size to 4, also occur OOM problem ？
  I know maybe the OOM problem because of model save and eval, but I don't know the OOM problem more specific.
  ### Environment information
  python /root/anaconda3/lib/python3.6/site-packages/tensor2tensor/bin/t2t_trainer.py --data_dir=./data_dir \
                                                                                      --problem=translate_enzh_bpe50k \
                                                                                      --model=transformer \
                                                                                      --hparams="batch_size=4" \
                                                                                      --hparams_set=transformer_base_single_gpu \
                                                                                      --output_dir=./en_zh_model \
                                                                                      --schedule=continuous_train_and_eval \
                                                                                      --train_steps=900000 \
                                                                                      --t2t_usr_dir=user_dir
  process the english data with bpe. 
  python 3.7
  tensor2tensor == 1.9.0
  tensorflow-gpu == 1.12.0
  ![屏幕快照 2021-04-22 上午10 30 12](https://user-images.githubusercontent.com/33311822/115647151-e71e4380-a355-11eb-81f4-fa8e3e0e1b88.png)
  
  ```
  OS: <your answer here>
  
  $ pip freeze | grep tensor
  # your output here
  
  $ python -V
  # your output here
  ```
  
  ### For bugs: reproduction and error logs
  
  ```
  # Steps to reproduce:
  ...
  ```
  
  ```
  # Error logs:
  ...
  ```
  