Is your model with the Dropout working or are you getting the OOM error now all the time?
Maybe a process still lives and uses all your GPU memory? Could you check it? I don’t know, if nvidia-smi works on a windows machine.
The volatile flag is deprecated. Since you are using pytorch 0.4.0, you should use with torch.no_grad() instead.
Did you observe the memory? Is it growing once you add Dropout to your model?