text: Title: GPU not using more than 2
  Body: Hi. I am trying to train the model.
  
  Currently, I am training the model with the following configurations : 
  
  num_threads = 64
  batch_size = 2
  
  load_size = 1024
  crop_size = 512
  
  In this setting, it only uses 2 gpus.
  
  If I increase the batch size, the number of GPU usage increases accordingly. 
  
  That is, batch size of 4 results to using 4 GPUs, batch size of 8 results to using 8 GPUs and etc.
  
  However, if I increase the batch size more than 2, CUDA out of memory error pops out.
  
  How can I increase the batch size? is decreasing the load_size only option?
  
  Thank you
  
  