Revert "Revert " lowmemorykiller: use swapfree instead of swaptotal for better memory reclaim""

This reverts commit a864ddf89b307400ca23772cfac663b0fd79c601.
Revert " lowmemorykiller: also count zram swapfile usage"

This reverts commit ef1b97202f93db6dffe9b5c4e1429203846f4f82.
Revert " lowmemorykiller: use swapfree instead of swaptotal for better memory reclaim"

This reverts commit 77a1d88e06114495f3e1a2f815d304cfad83d17a.