alt Hacker NewsThat’s clever. Makes for terrible UX, though.
AFAIK the only way for you to figure out how much of your disks is actually cached involves enumerating all tmpfs and ramfs mounts, summing their sizes, and subtracting the sum from the cache size reported by the kernel.
Ostensibly you could subtract "Shmem"[1] in /proc/meminfo from the cached value... maybe?
Do agree it's not the best UX and utilities should probably do a better job at showing that
[1]: https://man7.org/linux/man-pages/man5/proc_meminfo.5.html