I am also encountring strange lock-ups with high traffic situation on DUMMYNET. 
I have managed to avoid those lock-ups by adjusting the granularity of the
kernel
options     HZ=1000  # originally 100


Quoting Sergey Gershtein <[EMAIL PROTECTED]>:

> On Thursday, January 31, 2002 Peter Jeremy wrote:
> 
> PJ> It looks like you've run out of kernel memory.  At a quick guess, one
> PJ> of the nfsd processes is trying to open a file and can't allocate
> PJ> space for another inode whilst holding locks on other inodes.  The
> PJ> lockup is either due to the lack of KVM, or the inode locks are
> PJ> migrating up towards root and gathering more processes under their
> PJ> clutches until nothing can run.
> 
> PJ> If you monitor the memory usage with "vmstat -m", you should be
> PJ> able to see the free memory drop to zero, possibly all eaten by
> PJ> the "FFS node".
> 
> I've set up a cron job to monitor vmstat -m every 5 minutes so I can see
> what happens just before the next lock-up.
> 
> >>By the way, the file system that is being backuped has a lot (more
> >>than 1,000,000) of small files (less than 1Kb each).
> 
> PJ> That triggers a faint memory about a problem with doing this, but
> PJ> I thought it was now fixed.  How old are your sources?
> 
> RELENG_4_4 cvsuped a week ago (Jan 24th).  For some reason we don't
> cvsup 4.5 until it becomes RELEASE.
> 
> PJ> Increasing the amount of physical RAM increases the amount of KVM
> PJ> required to manage the RAM, reducing the amount of memory available
> PJ> for other things.  I didn't keep your original posting and I can't
> PJ> remember what MAXUSERS is set to - from memory it is either 128
> PJ> (which seems too small) or 1024 (which seems too large).  Try altering
> PJ> maxusers to 400-500 and see if that helps.
> 
> The initial value of MAXUSERS was 512, I tried lowering it to 128
> according to Doug White's advice, but it did not help.  Another server
> with the same hardware (which does not lock up) has MAXUSERS 1024, but
> it also does not have over 1,000,000 small files to backup.
> 
> PJ> If you still have problems, I think you'll need one of the FS gurus.
> 
> My hope was to find gurus on this list, I have no clue where else I
> can search for them. :(
> 
> Nevertheless, thank you for your help!
> 
> Regards,
> Sergey Gershtein
> 
> 
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