Date: Sat, 20 Nov 2004 21:02:41 +0200 From: Ruslan Ermilov <ru@FreeBSD.org> To: Bruce Evans <bde@zeta.org.au> Cc: Bosko Milekic <bmilekic@FreeBSD.org> Subject: Re: Too many mbufs Message-ID: <20041120190241.GC27369@ip.net.ua> In-Reply-To: <20041120225023.V86199@delplex.bde.org> References: <Pine.BSF.4.60.0411191757010.75856@mail.sbb.co.yu> <bf8d7e4904111912214a86a151@mail.gmail.com> <20041119204208.GA92096@ip.net.ua> <20041120225023.V86199@delplex.bde.org>
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On Sat, Nov 20, 2004 at 10:57:30PM +1100, Bruce Evans wrote:
> On Fri, 19 Nov 2004, Ruslan Ermilov wrote:
>=20
> > On Fri, Nov 19, 2004 at 03:21:44PM -0500, Chris McDermott wrote:
> > ...
> > > If I try and get the value with sysctlbyname() [copied from
> > > netstat/mbuf.c], it returns negative values for mbstat->m_mbufs. This
> > > negative value does fluctuate with network usage though...
> > >
> > > Test code:
> > > ...
> > > if (sysctlbyname("kern.ipc.mbstat", mbstat, &mlen, NULL, 0) < 0)
> > > perror("sysctl: retrieving mbstat");
> > >
> > > printf("mbufs: %d \nclusters: %d\n", mbstat->m_mbufs, mbstat->m_mclu=
sts);
> > >
> > > return 0;
> > > }
> > >
> > Your code is broken. Both m_mbufs and m_mclusts are of the type
> > u_long, so they should be printed with "%lu" specifier. Fix your
> > program and try again. (And you should see the same big number.)
> >
> > > Output:
> > >
> > > mbufs: -2240
> > > clusters: -2686
> > > ..
> > > codefactory# netstat -m
> > > 18446744073709549940 mbufs in use
> > > 18446744073709549630/17152 mbuf clusters in use (current/max)
>=20
> The value is obviously negative (since 1844mumble is nearly 2^64),
> so the buggy program accidentally displays the correct value.
>=20
Yes, sure. ;)
> I can't see why the count would be decremented below 0 more on 64-bit
> machines than on 32-bit ones.
>=20
I glanced at the kern_mbuf.c code yesterday responsible for mbstat
maintenance, and if it's supposed to be re-entrant (e.g., by multiple
CPUs), then there's a problem as accesses to mbstat aren't arbitrated.
I may be equally wrong on this. ;)
Cheers,
--=20
Ruslan Ermilov
ru@FreeBSD.org
FreeBSD committer
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