Hello, Marina!

Found misleading info on next pages:

• russian version:
  https://www.zabbix.com/documentation/current/ru/manual/appendix/items/vm.memory.size_params

  Linux 3.14+	/proc/meminfo, “Cached”:+“MemAvailable:”
  

• english version:
  https://www.zabbix.com/documentation/current/manual/appendix/items/vm.memory.size_params

  Linux 3.14+
  (also backported to 3.10 on RHEL 7)	/proc/meminfo, see "MemAvailable" in Linux kernel documentation for details.
  Note that free + buffers + cached is no longer equal to 'available' due to not all the page cache can be freed and low watermark being used in calculation.
  

regards,
Andrey