This is one of those things that is best baselined. If you are not seeing any network issues (i.e. connectivity losses or performance problems), and you see a consistent amount of free memory, then you can probably just adjust the threshold to a lower value.
If, however, you do suspect some network issues, or the amount steadily decreases, it would be good to explore this with TAC, or LAN switching forum as you could have a memory leak, or you may be over-taxing the devices.
As for where the memory is going, show proc mem or show mem summ can tell you that.
