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From Chuck Murcko <ch...@n2k.com>
Subject Re: WWW Form Bug Report: "sockets left in FIN_WAIT_2 lingering state" on SunOS 4.x (fwd)
Date Sun, 22 Dec 1996 03:03:44 GMT
Marc Slemko liltingly intones:
> 
> On Sat, 21 Dec 1996, Chuck Murcko wrote:
> 
> [...]
> > It also strengthens my suspicion that the limiting factor on how many
> > FIN_WAIT_2 connects a machine can tolerate is driven more by hitting the
> > limit of the list used to maintain them than by lossage of RAM. We're
> > definitely not out of RAM when our BSDI boxes panic.
> 
> Does BSD/OS implement TCP PCB hashing?  If not, you could be running
> into trouble trying to search a huge linked list, although that
> should just slow things to a crawl not crash things.  If it does
> implement tcpcb hashing, you could be running low on space in the
> hash table, causing undesirable results.  It may simply be running
> out of mbuf_clusters, but it could also be something in the tcpcb
> code.
> 
> If you can talk to the right person at BSDI, they may give you some
> help with figuring out what is going on and, more importantly,
> getting it fixed.  ...although finding the right person may be none
> too easy.
> 
I think you're on the money with out of space in the hash table, Marc.
As I said originally, on a machine with NMBCLUSTERS=4096, we see panic
basically when we run out of them. Since (as you show) that number
of mbuf clusters is nowhere near running the machine out of memory,
it seems Very Bad Things are starting to happen when the 4097th mbuf
cluster starts to get processed in the list, or when it fails to get
processed in the list, and something else in the kernel doesn't realize
it.

BSDI is (I believe) implementing a timeout for FIN_WAIT_2 state to get
around the original problem. At least, they're aware of that.

This is something else entirely.

Anyone know if Tony Sanders is still around here?

chuck
Chuck Murcko	N2K Inc.	Wayne PA	chuck@telebase.com
And now, on a lighter note:
Cogito cogito ergo cogito sum --
"I think that I think, therefore I think that I am."
		-- Ambrose Bierce, "The Devil's Dictionary"

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