Comment 53 for bug 1518457

For clarity here: I have not tested 15.04 and I can entirely believe that the issue doesn't appear on that version. I'm testing the specified kernel versions on Ubuntu 15.10 and the issue is reliably reproducible. It doesn't seem to depend on whether swap is enabled or how full the RAM is; large (~256MB) file writes are sufficient to provoke it. You'll see kswapd0 CPU usage spiking while writing large files; it doesn't always get stuck on 100%, but it's more likely to if the system has other disk activity (run another dd at the same time, grep a bunch of files, etc).