oil loss

I have a 2008 GMC Sierra 1500 Crew Cab V8. I took the vehicle in at 100,005 miles for an issue with white smoke occasionally coming out of the exhaust on a cold start. I was told of course warranty is past and they replaced what parts they could that were "covered" but I'm still losing oil...

Dealer says use oil life, so i've been going by oil life. Truck has 83,000 km. At 30% oil life and 9500 km since last oil change, oil level was down (caught me by surprise being a newer vehicle, I don't check oil as often as I should and now I will) at tip of dipstick. Added a litre and still...