Man this dog can eat

I have been feeding Watson the sensitive stomach adult food that I had for Hermes and it didn't seem to be any problem for him. We always feed the big dogs at the shelter 2 cups adult in the morning and 2 in the evening. I have been feeding Watson 2 cups and he devours it and he wants more. Some times he will eat as much as 3 or 4 cups in the morning and come back for 3-4 cups in the evening. I don't know if I am overfeeding him. He is a growing pup and doesn't appear to be getting fat. Even with this volume of food, he still wants treats. He is an eating machine.