Thanks for sharing, this was a great read. And it brought up some old memories, of fighting with telecom vendors about how their calculated their memory usage. At that time you only really got what the vendors gave you.

I think the most fun I had with the page cache was when one of the vendors "fixed" a bug where the memory calculation has previously excluded the page cache. These boxes were all network services, they didn't rely on the disk for anything more than holding the binaries, configuration, and logs. Where the fun comes in is the first time you grep through the logs, which fills the page cache, and sets off the alarms that the cellular network is about to die. ;)

Anyways, important concept to know and understand when it comes to how software performs when interacting with a host.