Unfortunatetly, no check_mk on that server.
When I sort processes by memory (either with HTOP or command line), I have exactly this :
ps -eo pmem,pcpu,vsize,pid,cmd | sort -k 1 -nr
As you can see, 22.6% + 7.4% + 0.4% + 0.4% + 0.2% + 0.1% + 0.1% + n * 0.0% is about 30% memory usage only.
So...