 Subtly Bad Things Linux May Be Doing To PostgreSQL 
Issues like the ones raised are why all sufficiently advanced database engine designs tend to evolve toward a kernel bypass architecture. From the perspective of a database engine, operating systems do a lot of "dumb" things with resource management and scheduling in ways that are essentially impossible to avoid that the database engine has enough context to do intelligently on its own. OS bypass in a database can have substantial performance benefits and add robustness for many edge cases. The obvious downside is that you basically end up rewriting the operating system in userspace, minus the device drivers, which is an enormous amount of work. It is not an incremental kind of design approach and it makes portability difficult. PostgreSQL actually does a really good job trying to be fast and robust without going to bypass internals.I've always asserted that the reason we've never seen a proper kernel bypass database engine in open source is that the Minimum Viable Product is too complex. A bare, stripped-down, low-level database engine that does full bypass of the operating system is usually at least 100kLoC of low-level C/C++, and that is before you add all the features a database user will actually want. That is a big initial investment by some people with fairly rare software design skills.