The standard kernel config for 16.04 has:
... CONFIG_MEMCG=y CONFIG_MEMCG_SWAP=y # CONFIG_MEMCG_SWAP_ENABLED is not set ...
I've not re-compiled with CONFIG_MEMCG_SWAP_ENABLED set to see if it fixes the issue.
The standard kernel config for 16.04 has:
... MEMCG_SWAP_ ENABLED is not set
CONFIG_MEMCG=y
CONFIG_MEMCG_SWAP=y
# CONFIG_
...
I've not re-compiled with CONFIG_ MEMCG_SWAP_ ENABLED set to see if it fixes the issue.