Julia garbage collector does not reclaim GPU memory

I'm trying to write Neural Style in MXNet.jl, and I keep running out of memory when I try to make new executors (and delete the old ones). My basic strategy is to store the executor in an `exec` variable and do

`exec = 0`
`gc()`

when I want to reclaim GPU memory for that executor. This does not work as expected, as I am tracking CUDA memory usage with `nvidia-smi` and there is never a drop in memory usage after calling `gc()`.

Does anyone know of a way to reclaim GPU memory? Here is my code for reference: https://github.com/bonsairobo/mxnet-neural-style/blob/master/stylenet.jl