This article provides information on which part of the memory will be consumed if there is any increase in traffic.
When traffic is being increased, "Used" memory should rise. When all available memory is consumed, it starts borrowing from Swap, so then "Swap used" would get increased. Cached/Buffered memory is generally booked in advance by applications for quick accesses. So it might be in use or maybe not. Whenever there is a new need of memory, Cached/Buffered memory is freed.
Having a big number in Cached/Buffer might actually be a good thing in that case, since it enhances application performance for which it is cached, but does not accurately depict Used memory.
For more information, we would recommend to look at RHEL manuals and forums, for "free" output.