I believe Volatile GPU-Util shows how active the GPU is while the 6.2 GB/8 GB is showing how much is on the GPU, according to Explained Output of nvidia-smi Utility | by Shachi Kaul | Analytics Vidhya | Medium

GPU-Util: It indicates the percent of GPU utilization i.e. percent of time when kernels were using GPU. For instance , output in table above shown 13% of the time. In case of low percent, GPU was under-utilised when if code spends time in reading data from disk (mini-batches).

I’m guessing there’s a lot going on in the code besides stuff processing on the GPU!