Comment 3 for bug 25098

I cannot confirm this on a Dapper or Breezy system. After copying a 300MB file on 2GB of RAM, RAM usage does increase, but that's due to increased cache and buffers. If sysctl's vm.swappiness is set too high, yes, that can cause unused programs to be swapped in favor of optimizing disk performance. There are circumstances where this actually boosts overall system performance (i.e. most servers).

Note that XFS caches read/write data a lot more aggressively than any other filesystem Linux has to offer, so expect more memory usage.

If you are a desktop user and want XFS's cache to back off if any program needs memory, edit /etc/sysctl.conf, add "vm.swappiness=5". This number ranges from 0 to 100, 0 favoring memory usage by applications and 100 favoring memory usage by cache. 60 is default. When set to 5, the cache will immediately back off whenever a program wants RAM, so swapping should stop. I've never dared to set it to 100, so whoever's bored can try that one.

To apply, either reboot or type in "sudo sysctl vm.swappiness=5"