Weird vmstat -s stats

[Lowell Gilbert]

Chris Pressey <cpressey at catseye.mb.ca> writes:

> 'Scuse me if I'm out of my depth here, but wouldn't the atomic 64-bit
> update only have to be done when the lower 32 bits were about to wrap
> (which would be relatively infrequent)?

Unfortunately, that doesn't quite work.  It opens up a race condition
where the counter wasn't about to wrap when you do the check, but
has been advanced again when you do the increment.

> The check to see if the lower 32 bits were about to wrap would be
> relatively cheap, too, I'd think.

Absolutely.  The problem is just that the check itself is not atomic.