Revert "Revert "mm: cma: don't replace lowmem pages with highmem""

This reverts commit 6d0bbee0eca10ad5bb16f4235dc514ac2720e4bb.
Revert "staging: android: lowmemorykiller: Add config option to support oom_adj values"

This reverts commit fd67559d497aa34a81c2df6d19a250295780c2e0.