Has anyone tested or flown permeable wings to increase efficiency? See this article: Aerodynamic Performance Improvements Due to Porosity in Wings at Moderate Re
Was wing porosity ever tested/used for real aircraft?
source:

The aerodynamic efficiency parameter clearly shows the positive effect of the permeability for low angles of attack. Having a permeable section on the airfoil surface will provide better aerodynamic characteristics when the angle of attack is less than 10°. This is compatible and in agreement with the observation of other researchers on the effect of the holes on the aerodynamics characteristics of the airfoil that concluded that “at a transitional phase where Re= 40,000 and the angle of attack ranged from 0 to 9°, the L/D ratio was higher compared to the same wing without holes
Not really a great answer but:
Tested - yes I believe so.  Actively used - not to my knowledge/unsure.  The structural complexity of this is challenging, and the cost to benefit probably isn't compelling enough for &quot;traditional&quot; configuration aircraft.
You may find this of interest A History of Suction-Type Laminar-Flow Control with Emphasis on Flight Research or Aerodynamics of Permeable Membrane Wings