(RH6) https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/deployment_guide/s2-proc-meminfo
https://www.thegeekdiary.com/understanding-proc-meminfo-file-analyzing-memory-utilization-in-linux/
https://linuxwiki.de/proc/meminfo

Active/Inactive: https://stackoverflow.com/questions/45487506/what-is-inactivefile-and-activefile-in-proc-meminfo