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

@@ -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
 

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

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

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()