malloc message with nfs transfer

[Robert Watson]

On Thu, 21 Aug 2003, cosmin wrote:

> > Sorry, just to be clear -- is the message you're getting on the NFS
> > client, or the NFS server?  Could you turn on debug.witness_ddb and get a
> > stack trace for the warning?
> 
> This is on the NFS server.  I turned on debug.witness_ddb, but I'm not
> sure if this will help, because the system isn't locking up, or
> otherwise stopping.  I have tried setting a breakpoint in ddb for
> 0xc4444ef0, but it starts breaking right away.  The malloc() messages
> are many minutes apart.

With witness_ddb turned on, the kernel should drop into ddb whenever
there's a witness-related warning, which should include the warnings you
mentioned in your previous e-mail.

> I'm not sure if these messages indicate anything critical.  I was mainly
> concerned with the nfs performance.

Generally speaking, WITNESS warns about potential problems, as opposed to
actual problems: i.e., it warns when a deadlock "would have occurred", if
the timing had been just right.  This was a warning that a potentially
blocking activity was performed while holding a mutex, which is generally
a bad idea.  A little bit more detail on the strack trace should be
sufficient to track it down.  Turning off WITNESS should dramatically
improve performance at the risk of lowering debugging output (maybe that's
not a risk :-).

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert at fledge.watson.org      Network Associates Laboratories