https://www.zabbix.com/documentation/current/en/manual/appendix/items/proc_get

Current implementation gives a lot of metrics (which are helpful), but none of them can provide +/- real values of RAM usage without complex math, this makes troubleshooting memory leaks and other memory consumptions issues quite complex with Zabbix only tool. 

Example how it can be gathered and calculated (PSS): https://github.com/pixelb/ps_mem

Adding PSS gathering to proc.get[] will alow to have nice template like this without external tools/scripts: