This feature is not available in Linux 3.10 which comes with CentOS 7.0.

The change was commited two years later:

[*"mm/oom_kill: count global and memory cgroup oom kills"*][1]


 [1]: https://github.com/torvalds/linux/commit/8e675f7af50747e1e9e96538e8706767e4f80e2c