At start up it shows some white smoke which enlarges and disappear when u ref.

Does it smell like anything? Sweet, like anti-freeze? It's a bit cold outside, so it's likely just condensation from the engine warming up, especially since it goes away. The only other thing it could be is coolant seeping into the cylinders after the engine is shut of (from the head gasket). If that's the case, the exhaust will smell a bit sweet as the engine is warming up. You'll want to have that inspected in the latter case. http://repairpal.com/mazda-within-10-miles-of-keller-virginia-23401