One side effect of this multigenerational production environment is that a new software release or configuration change might result in a system running healthily on one machine but experiencing an out-of-memory (OOM) issue on another. Facebook runs Linux as the host operating system on its machines. The traditional Linux OOM killer works fine in some cases, but in others it kicks in too late, resulting in the system entering a livelock for an indeterminate period.

source: L