How to decelerate during long downhill rides and avoid brake glazing
Brakes work by turning kinetic energy into heat through friction. As you heat up the system there generally is less capacity to absorb more heat (in addition to physical changes  in the brake system component).  

Constantly dragging your brakes is probably the worst strategy. Tandem bikes do this but they typically have one braking system dedicated to being a drag brake, and a separate braking system to be used for stopping. If the drag brake fails from overheating the primary brake system should be unaffected.

The reason constant drag braking is a bad strategy if you do not have a dedicated drag brake is as follows:


The brakes never get a chance to cool off, building up heat over time which can make them ineffective if for example you need to suddenly stop;
If you are drag braking to maintain a slow speed then you are not taking advantage for aerodynamic drag. Drag goes up with the cube of velocity. As such you get the highest braking force from aerodynamic drag the faster you go (yes it does sound crazy). 
If you are not effectively using aerodynamic drag you are forcing your brakes to do proportional more work (i.e., heat) than if you let your speed run up then brake.


Depending on your tolerance for speed (I am personally happy running my speed up to 90+ km/hr), the optimal strategy is to let your speed run up, do a period of braking where you drop your speed down (e.g., go from 80 km/hr down to 40 km/hr), let off the brakes and let your speed run up. This lets you cool off your brakes as well as use aerodynamic drag to your advantage. The key is to try and have long periods between a braking bought so you can get as much heat out of your brakes. If the period between a braking bought is too short (e.g., pulsing your brakes) you will start to get excessive heat build up in your brakes eventually leading to fade and even failure in some extreme circumstances.