The fact of the matter is that OS caches are shitty for anything other than what the OS does. This is why databases have bufferpools. The database knows best w

The fact of the matter is that OS caches are shitty for anything other than what the OS does. This is why databases have bufferpools. The database knows best what information stored in memory is useful. Look at the cache hit from a database bufferpool vs. an OS cache. It's abysmal. The OS makes the assumption that, if I got this page then I'll probably want the next 5 pages and pulls em in. That's great for sequential access because it's likely that you WILL need those pages but for random access it's horrid. And that's just disk. In the case of redis, the last thing you want is the OS determining what data is needed but isn't. At worse case, the data you need is spread across multiple pages and you can't really swap anything out. Systems that implement thier own memory management on top of the OS are typically ones that know the hot spots in the data in the first place.