Portion vs. Serving

I read somewhere that the difference between a serving size and portion is this, a serving size is what is recommended nutritionally, a portion is what you decide to eat. I often feel caught between these two. I often intellectually agree with the serving size, but yummy is yummy and it's hard to stop eating. A real goal for me right now is staying away from any gate way drugs that I know full well I can not control the portion size of, or being vigilant about pre-portioning, especially things like dried fruit and nuts. The great thing about not dieting is you can eat what you want there are no rules, the terrible news is it is on you to monitor and control. I feel like I am still wearing floaties in the deep end of the pool on that front.