Sure -- until your system crashes and data is left in an inconsistent state because some of it was written to non-volatile storage and some of it wasn't and your OS had no concept of transactional consistency because mmap is a leaky abstraction.

[UPDATE] I missed a crucial part of the problem setup, which is that the data is read-only. That obviously moots my objection.

I'm no systems programmer, but I remember trying to research mmap approach. It's been 3 years, so I'm not sure what stopped me, but something didn't feel right. Perhaps it was the lack of control over how memory is used. I could clearly see how not use it, and didn't want any fluctuations.

Edit: oh and I think I did come across some article like the one linked in the neighbor comment. It's starting to come back.

And Flatbuffers for data-layout and access.