If your roast has a layer of fat or skin on top, cut the top crosswise in slits, every 1/2 inch or so.
Place the pork loin in a bowl and cover with the oil, spices, and herbs. Massage in the spices and herbs into every part of the pork.
Preheat the oven for 5 minutes at 400°F (200°C).
Place the pork loin in a large baking gray along with the potatoes, and roast for 45 minutes, shaking and rotating them every 15 minutes or so, until the pork loin roast and potatoes are golden brown.