Memory used OID

Top will show you the total memory of the system, and total memory being used. In an F5 device you have the host system, CentOS that uses Linux as the kernel. On top (or aside, depends how you see this), you have the TMOS with TMM as the kernel.

At boot time, or when you change the provision, the system splits the memory. TMM will get the majority of the memory and pre-allocate it in the Linux kernel, the Linux will get the remaining of the memory.

Based in the name of the OID you are getting the value, that is host system.