Date: 06 Jul 2003 23:06:35 -0400 From: Lowell Gilbert <freebsd-stable-local@be-well.no-ip.com> To: stable@freebsd.org Subject: Re: Weird vmstat -s stats Message-ID: <44u19zxcg4.fsf@be-well.ilk.org> In-Reply-To: <20030706215545.1c29c5ed.cpressey@catseye.mb.ca> References: <200307051728.24681.me@farid-hajji.de> <44brw8g26e.fsf@be-well.ilk.org> <200307060029.00866.me@farid-hajji.de> <3F07576F.4030105@mac.com> <20030706213540.GU430@gsmx07.alcatel.com.au> <20030706215545.1c29c5ed.cpressey@catseye.mb.ca>
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Chris Pressey <cpressey@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.
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