That number reports the total amount of memory available to the GPU. From NVCtrl.h
* NV_CTRL_VIDEO_RAM - returns the total amount of memory available
* to the specified GPU (or the GPU driving the specified X
* screen). Note: if the GPU supports TurboCache(TM), the value
* reported may exceed the amount of video memory installed on the
* GPU. The value reported for integrated GPUs may likewise exceed
* the amount of dedicated system memory set aside by the system
* BIOS for use by the integrated GPU.