How does the Boeing 747 smoke evacuation work?
Looks like the smoke evacuation handle was used, but had little effect on the outcome. From the Final accident report of Boeing 747-44AF N571UP:


  The Captain called for the smoke evacuation handle to be pulled as the smoke accumulated in the cockpit. ... The smoke evacuation handle remained open for the remainder of the flight.


The report also has a note on its working:


  The smoke evacuation handle when pulled opens a port in the cockpit roof, which if the smoke is sustained and continuous, will draw smoke through the cockpit as the pressure is reduced by the open port ...


There is also a mention of it in the preliminary report:


  Smoke  Evacuation Handle –a  handle immediately  aft  of  the  P5  overhead panel that when pulled opens a circular, manually displaced vent in the  overhead fuselage section of the flight deck.


The final report also has an image of the exhaust port.



Smoke Evacuation Port (cockpit ceiling); image from Final accident report of Boeing 747-44AF N571UP