memory usage question

hello

I have ESXi 6.7 and run ubuntu 18.04
there have a question is
when I usage NVIDIA-SMI show memory-usage in ubuntu
the usage don’t match processes’s gpu usage

like pic
https://imgur.com/O4Aqhcn

I don’t have any processes running
but there have a 528M memory-usage
why ?
20200818_002.png