location of PEme

[Chenxu Cui]

I run some examples which are downloaded in https://github.com/Apress/programming-persistent-memory, I found it use disk instead of NVM to store or keep its persistence, because I use the function_pmem_is_pmem_ to check its type, the function return false showing it is not pmem. I just want to know how to how to keep a file persistent in NVM, or what the persistent file in NVM looks like.
I am a new-learner and do not understand its principle, and I would appricate if some body can help me.