Currently, memcg reclaim can disable swap token even if the swap token
mm doesn't belong in its memory cgroup. It's slightly risky. If an
admin creates very small mem-cgroup and silly guy runs contentious heavy
memory pressure workload, every tasks are going to lose swap token and
then system may become unresponsive. That's bad.
This patch adds 'memcg' parameter into disable_swap_token(). and if
the parameter doesn't match swap token, VM doesn't disable it.
Signed-off-by: KOSAKI Motohiro<kosaki.motohiro@xxxxxxxxxxxxxx>