From 033f96cc9313d7ceb3df14227ef3724ec3295d2a Mon Sep 17 00:00:00 2001
From: Bhasker Hariharan <bhaskerh@google.com>
Date: Fri, 31 May 2019 16:16:24 -0700
Subject: [PATCH] Change segment queue limit to be of fixed size.

Netstack sets the unprocessed segment queue size to match the receive
buffer size. This is not required as this queue only needs to hold enough
for a short duration before the endpoint goroutine can process it.

Updates #230

PiperOrigin-RevId: 250976323
---
 pkg/tcpip/transport/tcp/endpoint.go       | 4 +---
 pkg/tcpip/transport/tcp/endpoint_state.go | 2 +-
 pkg/tcpip/transport/tcp/protocol.go       | 4 ++++
 pkg/tcpip/transport/tcp/segment_queue.go  | 6 ++----
 4 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index b66610ee2..fd697402e 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -335,7 +335,7 @@ func newEndpoint(stack *stack.Stack, netProto tcpip.NetworkProtocolNumber, waite
 		e.probe = p
 	}
 
-	e.segmentQueue.setLimit(2 * e.rcvBufSize)
+	e.segmentQueue.setLimit(MaxUnprocessedSegments)
 	e.workMu.Init()
 	e.workMu.Lock()
 	e.tsOffset = timeStampOffset()
@@ -757,8 +757,6 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 		}
 		e.rcvListMu.Unlock()
 
-		e.segmentQueue.setLimit(2 * size)
-
 		e.notifyProtocolGoroutine(mask)
 		return nil
 
diff --git a/pkg/tcpip/transport/tcp/endpoint_state.go b/pkg/tcpip/transport/tcp/endpoint_state.go
index 27b0be046..e8aed2875 100644
--- a/pkg/tcpip/transport/tcp/endpoint_state.go
+++ b/pkg/tcpip/transport/tcp/endpoint_state.go
@@ -163,7 +163,7 @@ func (e *endpoint) loadState(state endpointState) {
 // afterLoad is invoked by stateify.
 func (e *endpoint) afterLoad() {
 	e.stack = stack.StackFromEnv
-	e.segmentQueue.setLimit(2 * e.rcvBufSize)
+	e.segmentQueue.setLimit(MaxUnprocessedSegments)
 	e.workMu.Init()
 
 	state := e.state
diff --git a/pkg/tcpip/transport/tcp/protocol.go b/pkg/tcpip/transport/tcp/protocol.go
index d31a1edcb..b31bcccfa 100644
--- a/pkg/tcpip/transport/tcp/protocol.go
+++ b/pkg/tcpip/transport/tcp/protocol.go
@@ -48,6 +48,10 @@ const (
 
 	// MaxBufferSize is the largest size a receive and send buffer can grow to.
 	maxBufferSize = 4 << 20 // 4MB
+
+	// MaxUnprocessedSegments is the maximum number of unprocessed segments
+	// that can be queued for a given endpoint.
+	MaxUnprocessedSegments = 300
 )
 
 // SACKEnabled option can be used to enable SACK support in the TCP
diff --git a/pkg/tcpip/transport/tcp/segment_queue.go b/pkg/tcpip/transport/tcp/segment_queue.go
index 3b020e580..e0759225e 100644
--- a/pkg/tcpip/transport/tcp/segment_queue.go
+++ b/pkg/tcpip/transport/tcp/segment_queue.go
@@ -16,8 +16,6 @@ package tcp
 
 import (
 	"sync"
-
-	"gvisor.googlesource.com/gvisor/pkg/tcpip/header"
 )
 
 // segmentQueue is a bounded, thread-safe queue of TCP segments.
@@ -58,7 +56,7 @@ func (q *segmentQueue) enqueue(s *segment) bool {
 	r := q.used < q.limit
 	if r {
 		q.list.PushBack(s)
-		q.used += s.data.Size() + header.TCPMinimumSize
+		q.used++
 	}
 	q.mu.Unlock()
 
@@ -73,7 +71,7 @@ func (q *segmentQueue) dequeue() *segment {
 	s := q.list.Front()
 	if s != nil {
 		q.list.Remove(s)
-		q.used -= s.data.Size() + header.TCPMinimumSize
+		q.used--
 	}
 	q.mu.Unlock()