Goldfish will eat whatever you give them in what ever amount you give, they do not have a stomach as such. They do not stop eating.
You have to limit the amount and ignore the little pleading faces as over feeding can be very detrimental to their health as well as the water quality.
Provide partially cooked vegetables for them to graze on throughout the day, mine go nuts for Broccoli, my goldies get sinking pellets, a days worth spread out over small feedings, the amount you will get to learn as each fish and tank are different. They also only get fed 3 days a week apart from the veggies which they have daily.