interesting. Dont think I've had that problem, so far every time it's been tmpfs with journald. tmpfs ram shows up as 'buffers' for some reason (since its disk related i guess? though flushing buffers of course wont solve it! thus I feel it's misreported in the wrong column and sent me goose chasing down the wrong way!)
your issue is different. you can dump caches as explained in another thread, but that costs the whole server by having no read cache for a while before it's repopulated again - suddenly reads on your drives will jump up til it is.
https://www.tecmint.com/clear-ram-memory-cache-buffer-and-swap-space-on-linux/
Still asking myself why nobody cares about the ram issues on containers.
Yes, but doesn't simply deleting the caches have any deficits?