Determine peer max requests based on receive speed

peerconn.go

@@ -47,6 +47,10 @@ type PeerRemoteAddr interface {
 	String() string
 }
 
+// Since we have to store all the requests in memory, we can't reasonably exceed what would be
+// indexable with the memory space available.
+type maxRequests = int
+
 type Peer struct {
 	// First to ensure 64-bit alignment for atomics. See #262.
 	_stats ConnStats
@@ -85,7 +89,8 @@ type Peer struct {
 
 	choking                                bool
 	requests                               map[Request]struct{}
-	requestsLowWater int
+	piecesReceivedSinceLastRequestUpdate   maxRequests
+	maxPiecesReceivedBetweenRequestUpdates maxRequests
 	// Chunks that we might reasonably expect to receive from the peer. Due to
 	// latency, buffering, and implementation differences, we may receive
 	// chunks that are no longer in the set of requests actually want.
@@ -114,7 +119,7 @@ type Peer struct {
 	peerTouchedPieces map[pieceIndex]struct{}
 	peerAllowedFast   bitmap.Bitmap
 
-	PeerMaxRequests  int // Maximum pending requests the peer allows.
+	PeerMaxRequests  maxRequests // Maximum pending requests the peer allows.
 	PeerExtensionIDs map[pp.ExtensionName]pp.ExtensionNumber
 	PeerClientName   string
 
@@ -470,8 +475,8 @@ func (cn *PeerConn) requestedMetadataPiece(index int) bool {
 }
 
 // The actual value to use as the maximum outbound requests.
-func (cn *Peer) nominalMaxRequests() (ret int) {
-	return int(clamp(1, int64(cn.PeerMaxRequests), 64))
+func (cn *Peer) nominalMaxRequests() (ret maxRequests) {
+	return int(clamp(1, 2*int64(cn.maxPiecesReceivedBetweenRequestUpdates), int64(cn.PeerMaxRequests)))
 }
 
 func (cn *Peer) totalExpectingTime() (ret time.Duration) {
@@ -1358,6 +1363,7 @@ func (c *Peer) receiveChunk(msg *pp.Message) error {
 	c.allStats(add(1, func(cs *ConnStats) *Count { return &cs.ChunksReadUseful }))
 	c.allStats(add(int64(len(msg.Piece)), func(cs *ConnStats) *Count { return &cs.BytesReadUsefulData }))
 	if deletedRequest {
+		c.piecesReceivedSinceLastRequestUpdate++
 		c.allStats(add(int64(len(msg.Piece)), func(cs *ConnStats) *Count { return &cs.BytesReadUsefulIntendedData }))
 	}
 	for _, f := range c.t.cl.config.Callbacks.ReceivedUsefulData {

request-strategy.go

@@ -53,6 +53,10 @@ func (cl *Client) doRequests() {
 			if p.closed.IsSet() {
 				return
 			}
+			if p.piecesReceivedSinceLastRequestUpdate > p.maxPiecesReceivedBetweenRequestUpdates {
+				p.maxPiecesReceivedBetweenRequestUpdates = p.piecesReceivedSinceLastRequestUpdate
+			}
+			p.piecesReceivedSinceLastRequestUpdate = 0
 			rst.Peers = append(rst.Peers, request_strategy.Peer{
 				HasPiece:    p.peerHasPiece,
 				MaxRequests: p.nominalMaxRequests(),