title: Zabbix Memory Used key
body: <p>I have an item that has vm.memory.size[used] as a key, this returns the memory used, this also included the cached and the buffers.</p>
  
  <p>I need to subtract vm.memory.size[cached] and vm.memory.size[buffers] from the vm.memory.size[used] to get the value that I need.</p>
  
  <p>How can I do this please since I cannot find a way to do this, this what I tried lately but deos not work.
  <a href="https://i.stack.imgur.com/PXT2S.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/PXT2S.jpg" alt="enter image description here"></a></p>