Revert "wgengine/netstack: increase gVisor's TCP send and receive buffer sizes (#12994)"

This reverts commit d9d9d525d9a03e750697f7a1218cb65b16ca4c60.

Updates tailscale/corp#22348

Signed-off-by: Jordan Whited <jordan@tailscale.com>

wgengine/netstack/netstack.go

@@ -245,44 +245,6 @@ const nicID = 1
 // have a UDP packet as big as the MTU.
 const maxUDPPacketSize = tstun.MaxPacketSize
 
-func setTCPBufSizes(ipstack *stack.Stack) error {
-	// tcpip.TCP{Receive,Send}BufferSizeRangeOption is gVisor's version of
-	// Linux's tcp_{r,w}mem. Application within gVisor differs as some Linux
-	// features are not (yet) implemented, and socket buffer memory is not
-	// controlled within gVisor, e.g. we allocate *stack.PacketBuffer's for the
-	// write path within Tailscale. Therefore, we loosen our understanding of
-	// the relationship between these Linux and gVisor tunables. The chosen
-	// values are biased towards higher throughput on high bandwidth-delay
-	// product paths, except on memory-constrained platforms.
-	tcpRXBufOpt := tcpip.TCPReceiveBufferSizeRangeOption{
-		// Min is unused by gVisor at the time of writing, but partially plumbed
-		// for application by the TCP_WINDOW_CLAMP socket option.
-		Min: tcpRXBufMinSize,
-		// Default is used by gVisor at socket creation.
-		Default: tcpRXBufDefSize,
-		// Max is used by gVisor to cap the advertised receive window post-read.
-		// (tcp_moderate_rcvbuf=true, the default).
-		Max: tcpRXBufMaxSize,
-	}
-	tcpipErr := ipstack.SetTransportProtocolOption(tcp.ProtocolNumber, &tcpRXBufOpt)
-	if tcpipErr != nil {
-		return fmt.Errorf("could not set TCP RX buf size: %v", tcpipErr)
-	}
-	tcpTXBufOpt := tcpip.TCPSendBufferSizeRangeOption{
-		// Min in unused by gVisor at the time of writing.
-		Min: tcpTXBufMinSize,
-		// Default is used by gVisor at socket creation.
-		Default: tcpTXBufDefSize,
-		// Max is used by gVisor to cap the send window.
-		Max: tcpTXBufMaxSize,
-	}
-	tcpipErr = ipstack.SetTransportProtocolOption(tcp.ProtocolNumber, &tcpTXBufOpt)
-	if tcpipErr != nil {
-		return fmt.Errorf("could not set TCP TX buf size: %v", tcpipErr)
-	}
-	return nil
-}
-
 // Create creates and populates a new Impl.
 func Create(logf logger.Logf, tundev *tstun.Wrapper, e wgengine.Engine, mc *magicsock.Conn, dialer *tsdial.Dialer, dns *dns.Manager, pm *proxymap.Mapper, driveForLocal drive.FileSystemForLocal) (*Impl, error) {
 	if mc == nil {
@@ -323,10 +285,6 @@ func Create(logf logger.Logf, tundev *tstun.Wrapper, e wgengine.Engine, mc *magi
 			return nil, fmt.Errorf("could not disable TCP RACK: %v", tcpipErr)
 		}
 	}
-	err := setTCPBufSizes(ipstack)
-	if err != nil {
-		return nil, err
-	}
 	linkEP := channel.New(512, uint32(tstun.DefaultTUNMTU()), "")
 	if tcpipProblem := ipstack.CreateNIC(nicID, linkEP); tcpipProblem != nil {
 		return nil, fmt.Errorf("could not create netstack NIC: %v", tcpipProblem)
@@ -551,7 +509,9 @@ func (ns *Impl) Start(lb *ipnlocal.LocalBackend) error {
 		panic("nil LocalBackend")
 	}
 	ns.lb = lb
-	tcpFwd := tcp.NewForwarder(ns.ipstack, tcpRXBufDefSize, maxInFlightConnectionAttempts(), ns.acceptTCP)
+	// size = 0 means use default buffer size
+	const tcpReceiveBufferSize = 0
+	tcpFwd := tcp.NewForwarder(ns.ipstack, tcpReceiveBufferSize, maxInFlightConnectionAttempts(), ns.acceptTCP)
 	udpFwd := udp.NewForwarder(ns.ipstack, ns.acceptUDP)
 	ns.ipstack.SetTransportProtocolHandler(tcp.ProtocolNumber, ns.wrapTCPProtocolHandler(tcpFwd.HandlePacket))
 	ns.ipstack.SetTransportProtocolHandler(udp.ProtocolNumber, ns.wrapUDPProtocolHandler(udpFwd.HandlePacket))

wgengine/netstack/netstack_tcpbuf_default.go

@@ -1,20 +0,0 @@
-// Copyright (c) Tailscale Inc & AUTHORS
-// SPDX-License-Identifier: BSD-3-Clause
-
-//go:build !ios
-
-package netstack
-
-import (
-	"gvisor.dev/gvisor/pkg/tcpip/transport/tcp"
-)
-
-const (
-	tcpRXBufMinSize = tcp.MinBufferSize
-	tcpRXBufDefSize = tcp.DefaultSendBufferSize
-	tcpRXBufMaxSize = 8 << 20 // 8MiB
-
-	tcpTXBufMinSize = tcp.MinBufferSize
-	tcpTXBufDefSize = tcp.DefaultReceiveBufferSize
-	tcpTXBufMaxSize = 6 << 20 // 6MiB
-)

wgengine/netstack/netstack_tcpbuf_ios.go

@@ -1,24 +0,0 @@
-// Copyright (c) Tailscale Inc & AUTHORS
-// SPDX-License-Identifier: BSD-3-Clause
-
-//go:build ios
-
-package netstack
-
-import (
-	"gvisor.dev/gvisor/pkg/tcpip/transport/tcp"
-)
-
-const (
-	// tcp{RX,TX}Buf{Min,Def,Max}Size mirror gVisor defaults. We leave these
-	// unchanged on iOS for now as to not increase pressure towards the
-	// NetworkExtension memory limit.
-	// TODO(jwhited): test memory/throughput impact of collapsing to values in _default.go
-	tcpRXBufMinSize = tcp.MinBufferSize
-	tcpRXBufDefSize = tcp.DefaultSendBufferSize
-	tcpRXBufMaxSize = tcp.MaxBufferSize
-
-	tcpTXBufMinSize = tcp.MinBufferSize
-	tcpTXBufDefSize = tcp.DefaultReceiveBufferSize
-	tcpTXBufMaxSize = tcp.MaxBufferSize
-)