[collectd] Confusion regarding metric names

[Dennis Jacobfeuerborn]

Hi,
I'm trying to figure out how I can get collectd supplied data into
influxdb and it's tag based format.
My issue right now is that I'm not 100% sure I understand the metric
format used by collectd. Take this metric for example:

<host>.cpu-3.cpu-idle 99.600929 1433256464

This seems to conform to the format
"<host>.<plugin>-<plugin-instance>.<type>-<type-instance>". This value
however:

<host>.vmem.vmpage_io-swap.in 0.000000 1433256464

seems to have a plugin "vmem", no plugin-instance, a type of "vmpage_io"
and a type instance of "swap". What does the ".in" represent though?

Regards,
  Dennis