Weird vmstat -s stats

[Lowell Gilbert]

Farid Hajji <me at farid-hajji.de> writes:

> > > "vmstat -s" shows on one of my boxes (uptime: 26 days):
> > >
> > > -1597015721 total name lookups
> > >           cache hits (101% pos + 0% neg) system 0% per-directory
> > >           deletions 0%, falsehits 0%, toolong 0%
> > >
> > > Weird. I'll have to cvsup again and hope this has been fixed :)
> >
> > I'm not seeing it on an up-to-date -STABLE.  Of course, that doesn't
> > mean much, because it looks like a counter wraparound.
> 
> Of course it's a wraparound.

The total count is a wraparound, but the positive cache hit count
still looks funny.

>                              I was not able to reproduce this
> condition on newer -STABLE. It takes some weeks of uptime
> and heavy use to reach this stage, unless you happen to know
> how to increment the counter with a test program (I don't
> know how).

You'd have to put in an extra kernel interface for that; the ability
to zero the structure would be (slightly) more useful.

> Shouldn't such counters be at least 64 bit wide?

They are, on most platforms.  You can't do that on an i386, though.
At least, not without opening up worse problems.