I'll add a couple of points to Daniel's summary: 1) initially I performed the test with the memeaters within a gui (KDE, but I tried gnome too). The system freezes occur when the test is performed within a gui. 2) Then, to isolate what seemed to be more symptoms (the freezes) than the problem itself, I started to perform the test using just text consoles. In these conditions there are no big, visible, system freezes. Although one of the tools used to snapshot vmstat (Michal's read_vmstat) complains with messages like "it took 28s to snapshot!" or something like that, so maybe there are still slowdowns. 3) Anyways, both in gui and text "mode", the test always causes a huge swap activity which seems to be disproportionate given the low pressure the vm is put under (tried as low as 4Mb/s allocation rate). 4) These are the swap configurations in which the huge swap activity occurs: -luks encrypted swap partition -dmcrypt plain swap partition -unencrypted swapfile located inside an encrypted, luks or dmcrypt plain, filesystem 5) The test does not cause any huge swap activity under these swap configs *when performed without a gui*: a) unencrypted swap partition b) encrypted swap file located inside and unencryted ext4 filesystem (that is ext4 directly on the partition and the directory in which the swapfile resides is encrypted with fs-level encryption, thus no dm-crypt involved). 6) I was particularly happy about b) above because it seemed to be a viable workaround, but sadly I have to report that, although the test does not causes large swap activity with b), minute-long system freezes are occurring during normal usage even with b). These seem to be the same kind of freezes that prompted me to find a way to reliably reproduce them under controlled conditions. I haven't yet performed the test with b)+gui, though, only b)+text console as I wrote in 5.
