Monitoring the GPU and GPU memory (VRAM) utilization on Windows is easy. There are many general tools, including specific tools supplied by your GPU vendor (like MSI's Afterburner or EVGA's Precision). Sadly, there is not a single tool on Linux that can monitor your GPU and show as many stats in a convenient GUI.
The best solution I have found is to open NVIDIA X Server Settings. In the section about your GPU, you can monitor these values:
Sadly, there is no graphing tools to view these values over time.
Tried with: NVIDIA driver 346.46 and Ubuntu 14.04