Support for /proc/vmstat

[zerkms]

Perhaps it is relevant to some other opened and closed issues, but I honestly haven't found any.

What I found is that both pswpin and pswpout are taken directly from the host, not the container.

# cat /proc/vmstat |grep pswp
pswpin 20245552
pswpout 21097647

As it was explained by Serge Hallyn at #202 (comment) there is a chance it might not be possible to have it implemented, but posting it anyway just for the record.