IFS 10 Buffer/Cache usage

Hello,

we have a IFS10 UPD7 having 3 node application cluster on Linux. Each node is having 64 GB RAM.

while checking the memory usage. Master node is taking 44 GB of Buffer/cache and other 2 nodes are taking 35GB of Buffer/cache.

So Master node is actually using 99% memory. 

can you suggest  - 

1. Why there is too much of buffer/cache used. 
2. is there any cycle when this will reduce.
3. what can we do to optimize the same

Let me know if more info is required on the same. 

Best Regards

Pankaj