I see sometimes Linux based servers using the swap when it is not necessary. Especially when all of the free ram is used for caching. But now my dedicated server with 16GB RAM begins to swap, although there is enough RAM free:
$ free -m total used free shared buffers cached Mem: 16029 10035 5994 0 421 8508 -/+ buffers/cache: 1104 14925 Swap: 19322 3 19319
The server is running a web-server, php and a database which never use all of the 16GB. There should be no need to swap. But Linux still does this. In this case only 3MB but it's the principle.