Yeah I agree that one isn't very clear, perhaps the idea is to use `msync()` as a barrier to achieve consistent ordering of the writes without having to handle that yourself with more complex primitives. But then, they do mention some of those primitives at the bottom of the article, so it's hard to say what exactly the idea is.

mmap/msync is behavior is also very platform specific. On some systems (like AIX, at least older versions), even without msync, memory mapped data is synced back to disk periodically.

I worked on a code base that was portable between Linux, AIX, and some other Unix flavors. mmap/msync was a source of bugs. Just imagine your system running for days, never syncing any data to disk... then someone pulls the plug. Where'd my data go? Even worse, it happened "in production" at a beta site. Fortunately we had a way to recover data from a log.