This might not be CentOS related at all. Sorry about that.
I have lots of C6 & C7 machines in use and all of them have the default swappiness of 60. The problem now is that a lot of those machines do swap although there is no memory pressure. I’m now thinking about lowering swappiness to 1. But I’d still like to find out why this happens. The only common thing between all those machines is that there are nightly backups done with Bacula. I once came across issues with the fs-cache bringing Linux to start paging out. Any hints, explanations and suggestions would be much appreciated.