The answer: "it did actually not, you are not seeing the actual ram usage, because the os now counts it as filesystem cache. Since #613 the model is a memory mapped file. It does not do the impossible, it's just that gnome-system-monitor does not show cached files."
This is incredibly mundane; why is this on the front page?
Because it’s a response to a post that had a lot of hype on the front page yesterday
Looks like the mmap functionality was done by the same person as https://justine.lol what a great hacker!
If you have enough memory, I the entire file eventually is in memory because it doesn't need to be paged out. If it takes up less memory (because your memory is limited), it'll still need to page the file off disk when it hits the cache bounds.
80% percent of code writers probably never heard mmap, and might less than 1% ever use that.
It's truly magical. And flags like MAP_LOCKED, MAP_ANONYMOUS, MAP_POPULATE - you can tune it in closer to the behavior you want. That said, if you are concerned about memory consumption, you are ceding control to the kernel. It gets to decide when and whether to evict pages (though you can give hints).
qBittorrent builds using libtorrent 2.0 turned into an absolute memory hog because it used mmap. I assume it is the page table backing the hundred of GBs of memory mapped files. I remember seeing a joke issue asking the author to update the system requirements to be hundreds of GBs of RAM.
According to the PR on github this is likely just a bug with the implementation that makes htop (etc) display wrong RAM usage numbers. It seems as of now as there is "no magic happening". People reported much higher actual RAM usage. The author acknowledged that it might be a bug when he posted the PR.