I used to can potatoes when we were on the farm. I don't remember if I cooked them before canning, but I did own a pressure cooker, so I suppose I used it. They were very nice to slice into bacon grease in the frying pan. I loved the flavor.
Now I freeze mashed potatoes all the time. After a big party, there are often left over mashed potatoes. They freeze very well after they have other ingredients in them: butter, milk, sour cream and onion.
Freezing raw potatoes does not work. The ones you buy may have been blanched or something. I have tasted frozen raw potatoes, and will never do that again.