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methods called Vestigial Time-Wait (VTW) and Maximum Segment Lifetime Truncation (MSLT). MSLT and VTW were contributed by Coyote Point Systems, Inc. Even after a TCP session enters the TIME_WAIT state, its corresponding socket and protocol control blocks (PCBs) stick around until the TCP Maximum Segment Lifetime (MSL) expires. On a host whose workload necessarily creates and closes down many TCP sockets, the sockets & PCBs for TCP sessions in TIME_WAIT state amount to many megabytes of dead weight in RAM. Maximum Segment Lifetimes Truncation (MSLT) assigns each TCP session to a class based on the nearness of the peer. Corresponding to each class is an MSL, and a session uses the MSL of its class. The classes are loopback (local host equals remote host), local (local host and remote host are on the same link/subnet), and remote (local host and remote host communicate via one or more gateways). Classes corresponding to nearer peers have lower MSLs by default: 2 seconds for loopback, 10 seconds for local, 60 seconds for remote. Loopback and local sessions expire more quickly when MSLT is used. Vestigial Time-Wait (VTW) replaces a TIME_WAIT session's PCB/socket dead weight with a compact representation of the session, called a "vestigial PCB". VTW data structures are designed to be very fast and memory-efficient: for fast insertion and lookup of vestigial PCBs, the PCBs are stored in a hash table that is designed to minimize the number of cacheline visits per lookup/insertion. The memory both for vestigial PCBs and for elements of the PCB hashtable come from fixed-size pools, and linked data structures exploit this to conserve memory by representing references with a narrow index/offset from the start of a pool instead of a pointer. When space for new vestigial PCBs runs out, VTW makes room by discarding old vestigial PCBs, oldest first. VTW cooperates with MSLT. It may help to think of VTW as a "FIN cache" by analogy to the SYN cache. A 2.8-GHz Pentium 4 running a test workload that creates TIME_WAIT sessions as fast as it can is approximately 17% idle when VTW is active versus 0% idle when VTW is inactive. It has 103 megabytes more free RAM when VTW is active (approximately 64k vestigial PCBs are created) than when it is inactive.
29 lines
789 B
Makefile
29 lines
789 B
Makefile
# $NetBSD: Makefile,v 1.20 2011/05/03 18:28:45 dyoung Exp $
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INCSDIR= /usr/include/netinet
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INCS= icmp6.h icmp_var.h if_atm.h if_ether.h if_inarp.h igmp.h \
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igmp_var.h in.h in_gif.h in_pcb.h in_pcb_hdr.h \
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in_selsrc.h in_systm.h \
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in_var.h ip.h ip_carp.h ip6.h ip_ecn.h ip_encap.h \
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ip_icmp.h ip_mroute.h ip_var.h pim.h pim_var.h \
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tcp.h tcp_debug.h tcp_fsm.h tcp_seq.h tcp_timer.h tcp_var.h \
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tcpip.h udp.h udp_var.h \
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tcp_vtw.h
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# ipfilter headers
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# XXX shouldn't be here
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.include <bsd.own.mk>
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INCS+= ip_compat.h # always needed by kdump(1)
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.if (${MKIPFILTER} != "no")
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INCS+= ip_auth.h ip_fil.h ip_frag.h ip_htable.h ip_nat.h \
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ip_lookup.h ip_pool.h ip_proxy.h ip_scan.h ip_state.h ip_sync.h \
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ipl.h
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.endif
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.include <bsd.kinc.mk>
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.PATH: ${NETBSDSRCDIR}/sys/dist/ipf/netinet
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