kern/49973: odd swapping on idle system

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>Number:         49973
>Category:       kern
>Synopsis:       odd swapping on idle system
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jun 15 00:35:01 +0000 2015
>Originator:     Ben Gergely
>Release:        NetBSD 7.99.1
>Organization:
>Environment:
NetBSD 7.99.18 i386
>Description:
On a mostly Idle (idle apart from the xcalls) machine this occurs:

08 threads: 9 idle, 1 runnable, 95 sleeping, 1 stopped, 2 on CPU
CPU0 states:  0.0% user,  0.0% nice, 36.3% system,  0.2% interrupt, 63.5% idle
CPU1 states:  0.4% user,  0.0% nice, 50.3% system,  0.0% interrupt, 49.3% idle
Memory: 725M Act, 700M Inact, 2500K Wired, 32M Exec, 1263M File, 1202M Free
Swap: 1024M Total, 1024M Free

  PID   LID USERNAME PRI STATE      TIME   WCPU    CPU NAME      COMMAND
    0    63 root     126 RUN/0    106:08 41.70% 41.70% pgdaemon  [system]
    0     7 root     127 xcall/0   50:14 27.54% 27.54% xcall/0   [system]
    0    22 root     127 xcall/1   59:42 15.38% 15.38% xcall/1   [system] 

#pstat -T
338/3404 files
 110592 vnodes
0/2097585 blocks swap space

Removing the swap devices does not affect this.

>How-To-Repeat:
unknown
>Fix:
unknown