[CRIU] [PATCH 0/10] Half the amount of setns calls

[Pavel Emelyanov]

The setns call is slow when called two times or more. This
is because on the 2nd call kernel puts the last reference
to task's nsproxy (last, because it is fresh new since the
1st call, and on the 1st the previous was shared with parent).

This results in setns() taking up to 8% of time on p.haul test.
After this set the number of calls drops from 4 to 2 and the
resulting timing is ~2%.

As a side effect we have a nice preparation for multiple netns
support in networking code.

Thanks,
Pavel