i do top up engine oil once every month and smoky
My car has an automatic transmission.
If you are having to top off the oil once a month, depending on how many miles you drive per month, this may suggest that your engine is burning the oil. If the smoke is a blue colored smoke, this is an indication that the oil is being burnt with the fuel. When this happens, it is usually due to worn piston rings allowing the oil to pass by the pistons up into the combustion chamber.
This can also happen when the valve guide seals are bad, resulting in oil from the valve train leaking down into the combustion chamber as well. I would recommend having an expert from YourMechanic come to your location to inspect for the source of the smoke and suggest any needed repairs.