R loads all objects into virtual memory. This suggests that an active R session within a terminal multiplexer may end up consuming a lot of RAM if it was launched in interactive mode. Neither of top and htop commands return those interactive R sessions when no script/function is running. To see how much memory currently active processes are occupying, type
ps aux --sort user,-vsz To find out how much Swap is being used by a process,
grep VmSwap /proc/15181/status