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From: dab@oliver.cray.COM.UUCP
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Reassembly queues in TCP
Message-ID: <8705291425.AA06527@oliver.cray.uucp>
Date: Fri, 29-May-87 10:25:55 EDT
Article-I.D.: oliver.8705291425.AA06527
Posted: Fri May 29 10:25:55 1987
Date-Received: Sat, 30-May-87 10:32:23 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: world
Organization: The ARPA Internet
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Many months ago I ran into problems with running out of mbufs
on the Cray computers.  Among the problems was the one described
by Phil Wood, that of getting in lots of little (1 byte) packets,
and having one of the early ones get lost.  I did a twofold fix
to the Berkeley code (4.2, same mods apply to 4.3) to keep this
problem to a minimum.

	1) Compact the TCP reassembly queue.  The Berkeley code
	   does not compact the TCP reassembly queue.  If you
	   have 500 1 byte packets on your reassembly queue, you
	   are using up 500 mbufs.

	2) In uipc_mbuf.c, there is the comment in m_expand()
		/* should ask protocols to free code */
	   Well, I did just that.  I wrote a routine called
	   pfdrain(), almost identical to pfctlinput(). Then, I
	   also added code to the tcp_drain() routine to actually
	   go through all the tcp reassembly queues and free up
	   all the fragments.  Since we haven't acknowledged any
	   of it, it's no problem to toss it.

These mods are not very long, and I sent them to Mike Karels awhile
ago (but not in time for the release).  It took around 40 lines
of code to do the above mods.  Perhaps these fixes might show up
on the 4.3 bug list at some point.  If you are in urgent need of
this code, contact me directly.
			Dave Borman
			Cray Research, Inc.
			dab@umn-rei-uc.arpa