I am using the code from https://github.com/meetshah1995/pytorch-semseg 1 to train a model.  I have been training on 1 NVIDIA Titan V and am now trying training on 2 NVIDIA Titan Vs.
I am wrapping the model in DataParallel.  My understanding is that using 2 GPUs should enable me to increase my batch size but that is not the case.  When I increase the batch size by any amount over the number I had for one GPU, I get the same CUDA runtime out of memory  error  in THCStorage.cu that I got when I was finding the max batch size for 1 GPU.
Using nvidia-smi -a I see that in the 2-GPU setup, one GPU is using the same amount of frame buffer memory as in the 1-GPU setup and the second GPU is using about 2/3 of the frame buffer memory.