eth/connmanager: handle inbound and dialed peers separately

Signed-off-by: Csaba Kiraly <csaba.kiraly@gmail.com>

eth/backend.go

@@ -291,7 +291,8 @@ func New(stack *node.Node, config *ethconfig.Config) (*Ethereum, error) {
 	}
 
 	eth.connman = newConnManager(&connmanConfig{
-		maxDialPeers: eth.p2pServer.MaxDialedConns(),
+		maxDialPeers:    eth.p2pServer.MaxDialedConns(),
+		maxInboundPeers: eth.p2pServer.MaxInboundConns(),
 	})
 
 	eth.miner = miner.New(eth, config.Miner, eth.engine)

eth/connmanager.go

@@ -48,21 +48,25 @@ const (
 //   - during sync the Downloader handles peer connections co connManager is disabled
 //   - if not syncing and the peer count is close to the limit, it drops peers
 //     randomly every peerDropInterval to make space for new peers
+//   - peers are dropped separately from the inboud pool and from the dialed pool
 type connManager struct {
 	connmanConfig
 	peersFunc   getPeersFunc
 	syncingFunc getSyncingFunc
 
-	// the peerDrop timer introduces churn if we are close to limit capacity
-	peerDropTimer *mclock.Alarm
-	peerEventCh   chan *p2p.PeerEvent
-	sub           event.Subscription
+	// The peerDrop timers introduce churn if we are close to limit capacity.
+	// We handle Dialed and Inbound connections separately
+	peerDropDialedTimer  *mclock.Alarm
+	peerDropInboundTimer *mclock.Alarm
 
-	wg         sync.WaitGroup
+	peerEventCh chan *p2p.PeerEvent // channel for peer event changes
+	sub         event.Subscription  // subscription to peerEventCh
+
+	wg         sync.WaitGroup // wg for graceful shutdown
 	shutdownCh chan struct{}
 }
 
-// callback type to get the list of connected peers.
+// Callback type to get the list of connected peers.
 type getPeersFunc func() []*p2p.Peer
 
 // Callback type to get syncing status.
@@ -70,10 +74,11 @@ type getPeersFunc func() []*p2p.Peer
 type getSyncingFunc func() bool
 
 type connmanConfig struct {
-	maxDialPeers int // maximum number of dialed peers
-	log          log.Logger
-	clock        mclock.Clock
-	rand         *mrand.Rand
+	maxDialPeers    int // maximum number of dialed peers
+	maxInboundPeers int // maximum number of inbound peers
+	log             log.Logger
+	clock           mclock.Clock
+	rand            *mrand.Rand
 }
 
 func (cfg connmanConfig) withDefaults() connmanConfig {
@@ -95,10 +100,11 @@ func (cfg connmanConfig) withDefaults() connmanConfig {
 func newConnManager(config *connmanConfig) *connManager {
 	cfg := config.withDefaults()
 	cm := &connManager{
-		connmanConfig: cfg,
-		peerDropTimer: mclock.NewAlarm(cfg.clock),
-		peerEventCh:   make(chan *p2p.PeerEvent),
-		shutdownCh:    make(chan struct{}),
+		connmanConfig:        cfg,
+		peerDropDialedTimer:  mclock.NewAlarm(cfg.clock),
+		peerDropInboundTimer: mclock.NewAlarm(cfg.clock),
+		peerEventCh:          make(chan *p2p.PeerEvent),
+		shutdownCh:           make(chan struct{}),
 	}
 	cm.log.Info("New Connection Manager", "maxDialPeers", cm.maxDialPeers, "threshold", peerDropThreshold, "interval", peerDropInterval)
 	return cm
@@ -116,61 +122,74 @@ func (cm *connManager) Start(srv *p2p.Server, syncingFunc getSyncingFunc) {
 // Stop the connection manager.
 func (cm *connManager) Stop() {
 	cm.sub.Unsubscribe()
-	cm.peerDropTimer.Stop()
+	cm.peerDropInboundTimer.Stop()
+	cm.peerDropDialedTimer.Stop()
 	close(cm.shutdownCh)
 	cm.wg.Wait()
 }
 
-// numDialPeers returns the current number of peers dialed (not inbound).
-func (cm *connManager) numDialPeers() int {
-	dialed := slices.DeleteFunc(cm.peersFunc(), (*p2p.Peer).Inbound)
-	return len(dialed)
-}
-
-func (cm *connManager) numPeers() (int, int, int) {
+// numPeers returns the current number of peers and its breakdown (dialed or inbound).
+func (cm *connManager) numPeers() (numPeers int, numDialed int, numInbound int) {
 	peers := cm.peersFunc()
 	dialed := slices.DeleteFunc(peers, (*p2p.Peer).Inbound)
 	return len(peers), len(dialed), len(peers) - len(dialed)
 }
 
 // dropRandomPeer selects one of the peers randomly and drops it from the peer pool.
-func (cm *connManager) dropRandomPeer() bool {
+func (cm *connManager) dropRandomPeer(dialed bool) bool {
 	peers := cm.peersFunc()
 
-	// Only drop from dyndialed peers. Avoid dropping trusted peers.
-	// Give some time to peers before considering them for a drop.
 	selectDoNotDrop := func(p *p2p.Peer) bool {
-		return !p.DynDialed() ||
-			p.Trusted() ||
-			p.Lifetime() < mclock.AbsTime(doNotDropBefore)
+		if dialed {
+			// Only drop from dyndialed peers. Avoid dropping trusted peers.
+			// Give some time to peers before considering them for a drop.
+			return !p.DynDialed() ||
+				p.Trusted() ||
+				p.Lifetime() < mclock.AbsTime(doNotDropBefore)
+		} else {
+			// Only drop from inbound peers. Avoid dropping trusted peers.
+			// Give some time to peers before considering them for a drop.
+			return p.DynDialed() || p.StaticDialed() ||
+				p.Trusted() ||
+				p.Lifetime() < mclock.AbsTime(doNotDropBefore)
+		}
 	}
 	droppable := slices.DeleteFunc(peers, selectDoNotDrop)
 	if len(droppable) > 0 {
 		p := droppable[cm.rand.Intn(len(droppable))]
-		cm.log.Debug("dropping random peer", "id", p.ID(), "duration", common.PrettyDuration(p.Lifetime()), "peercountbefore", len(peers))
+		cm.log.Debug("dropping random peer", "id", p.ID(), "duration", common.PrettyDuration(p.Lifetime()),
+			"dialed", dialed, "peercountbefore", len(peers))
 		p.Disconnect(p2p.DiscTooManyPeers)
 		return true
 	}
 	return false
 }
 
-// updatePeerDropTimer checks and starts/stops the timer for peer drop.
-func (cm *connManager) updatePeerDropTimer(syncing bool) {
+// updatePeerDropTimers checks and starts/stops the timer for peer drop.
+func (cm *connManager) updatePeerDropTimers(syncing bool) {
 
-	numpeers, out, in := cm.numPeers()
+	numPeers, numDialed, numInbound := cm.numPeers()
 	cm.log.Trace("ConnManager status", "syncing", syncing,
-		"peers", numpeers, "out", out, "in", in, "maxout", cm.maxDialPeers)
+		"peers", numPeers, "out", numDialed, "in", numInbound,
+		"maxout", cm.maxDialPeers, "maxin", cm.maxInboundPeers)
 
 	if !syncing {
 		// If a drop was already scheduled, Schedule does nothing.
-		if cm.maxDialPeers-cm.numDialPeers() <= peerDropThreshold {
-			cm.peerDropTimer.Schedule(cm.clock.Now().Add(peerDropInterval))
+		if cm.maxDialPeers-numDialed <= peerDropThreshold {
+			cm.peerDropDialedTimer.Schedule(cm.clock.Now().Add(peerDropInterval))
 		} else {
-			cm.peerDropTimer.Stop()
+			cm.peerDropDialedTimer.Stop()
+		}
+
+		if cm.maxInboundPeers-numInbound <= peerDropThreshold {
+			cm.peerDropInboundTimer.Schedule(cm.clock.Now().Add(peerDropInterval))
+		} else {
+			cm.peerDropInboundTimer.Stop()
 		}
 	} else {
 		// Downloader is managing connections while syncing.
-		cm.peerDropTimer.Stop()
+		cm.peerDropDialedTimer.Stop()
+		cm.peerDropInboundTimer.Stop()
 	}
 }
 
@@ -193,22 +212,24 @@ func (cm *connManager) loop() {
 	for {
 		select {
 		case <-syncCheckTimer.C():
-			// Update info about syncing status, and rearm the timer.
+			// Update info about syncing status, and rearm the timers.
 			syncingNew := cm.syncingFunc()
 			if syncing != syncingNew {
-				// Syncing status changed, we might need to update the timer.
+				// Syncing status changed, we might need to update the timers.
 				cm.log.Trace("Sync status changed", "syncing", syncingNew)
 				syncing = syncingNew
-				cm.updatePeerDropTimer(syncing)
+				cm.updatePeerDropTimers(syncing)
 			}
 			syncCheckTimer.Schedule(cm.clock.Now().Add(syncCheckInterval))
 		case ev := <-cm.peerEventCh:
 			if ev.Type == p2p.PeerEventTypeAdd || ev.Type == p2p.PeerEventTypeDrop {
-				// Number of peers changed, we might need to start the timer.
-				cm.updatePeerDropTimer(syncing)
+				// Number of peers changed, we might need to start the timers.
+				cm.updatePeerDropTimers(syncing)
 			}
-		case <-cm.peerDropTimer.C():
-			cm.dropRandomPeer()
+		case <-cm.peerDropDialedTimer.C():
+			cm.dropRandomPeer(true)
+		case <-cm.peerDropInboundTimer.C():
+			cm.dropRandomPeer(false)
 		case <-cm.shutdownCh:
 			return
 		}