Submitted patch changes in src/libs/zbxsysinfo/linux/memory.c

• reordered functions VM_MEMORY_*() to put them in the order as they are used in
  VM_MEMORY_SIZE()
• added vm.memory.size[] key new parameters:

  vm.memory.size[active]
  vm.memory.size[anon]
  vm.memory.size[inactive]
  vm.memory.size[slabs]

• added new function VM_MEMORY_PROC_MEMINFO() which is used to handle new vm.memory.size[] parameters
• use VM_MEMORY_PROC_MEMINFO() to handle:

  vm.memory.size[cached]

Please let me know if you are happy to add something like this.
If yes I'll try to add handle more /prc/meminfo entries.

Patch can be cleanly applied against 3.4 and trunk and probably against older branches as well.