See OpenCL, any other buffer mechanism at hand
Openfb had this problem only 12 and 15 years ago, so it's understandable that OpenCL, which doesn't allocate specific memory (only something free on the scoreboard) and which can have quite a long callback in being asked to clear the buffer used would have a hitch or so coughing up a callback for a clear displaylist. Or, your OS might use Persistent Mapped Buffers (OpenGL) and not be compiled to worry horribly about data load determinacy (v. callbacks w. new pointer optional) and reusing them. Quite normal if you're not running signboards in a government building! (Flying dockets! Tripletake defense-state!)
Either you want a fuzzer or active padding daemon competing (maybe with some determinism) with your power scheme to prevent leaks on displays of the same machine...reproduce it with lvm and you've earned an educational use case to ponder...or you really want to save power and noise.