In the June 2013 issue of ;login:, I wrote about future interfaces for nonvolatile memory (NVM). In it, I described an NVM programming model specification under development in the SNIA NVM Programming Technical Work Group (TWG). In the four years that have passed, the spec has been published, and, as predicted, one of the programming models contained in the spec has become the focus of considerable follow-up work. That programming model, described in the spec as NVM.PM.FILE, states that persistent memory (PM) should be exposed by operating systems as memory-mapped files. In this article, I’ll describe how the intended persistent memory programming model turned out in actual OS implementations, what work has been done to build on it, and what challenges are still ahead of us.
