:/opt/zabbix/sbin# ./zabbix_agentd -t 'vm.memory.size[available]'
vm.memory.size[available] [u|1418600448]

:/opt/zabbix/sbin# ./zabbix_agentd -t 'vm.memory.size[free]'
vm.memory.size[free] [u|1418600448]

:/opt/zabbix/sbin# ./zabbix_agentd -t 'vm.memory.size[used]'
vm.memory.size[used] [u|20056236032]


load averages: 3.46, 3.84, 3.98; up 35+02:34:54 11:46:05
110 processes: 109 sleeping, 1 on cpu
CPU states: 93.6% idle, 5.6% user, 0.9% kernel, 0.0% iowait, 0.0% swap
Memory: 20G phys mem, 7381M free mem, 40G total swap, 10G free swap

static int	VM_MEMORY_AVAILABLE(AGENT_RESULT *result)
{
	SET_UI64_RESULT(result, (zbx_uint64_t)sysconf(_SC_AVPHYS_PAGES) * sysconf(_SC_PAGESIZE));