really few white smoke coming out from the engine. Today I decide to check the engine oil. And After I open the hood, I found really light smoke coming out from the engine. And there is no smoke when the car is idling.

You most likely have an issue with your radiator, I would check all hoses and components for leaks. Please DO NOT drive your car if it starts to overheat. If you cannot diagnose the issue take it to a mechanic, they have the tools to find your leak and keep you driving safely.