Fix larger than necessary allocations in streamer (#8187)

core/src/packet.rs

@@ -9,7 +9,7 @@ use solana_metrics::inc_new_counter_debug;
 pub use solana_sdk::packet::{Meta, Packet, PACKET_DATA_SIZE};
 use std::{io::Result, net::UdpSocket, time::Instant};
 
-pub fn recv_from(obj: &mut Packets, socket: &UdpSocket) -> Result<usize> {
+pub fn recv_from(obj: &mut Packets, socket: &UdpSocket, max_wait_ms: usize) -> Result<usize> {
     let mut i = 0;
     //DOCUMENTED SIDE-EFFECT
     //Performance out of the IO without poll
@@ -20,9 +20,11 @@ pub fn recv_from(obj: &mut Packets, socket: &UdpSocket) -> Result<usize> {
     socket.set_nonblocking(false)?;
     trace!("receiving on {}", socket.local_addr().unwrap());
     let start = Instant::now();
-    let mut total_size = 0;
     loop {
-        obj.packets.resize(i + NUM_RCVMMSGS, Packet::default());
+        obj.packets.resize(
+            std::cmp::min(i + NUM_RCVMMSGS, PACKETS_PER_BATCH),
+            Packet::default(),
+        );
         match recv_mmsg(socket, &mut obj.packets[i..]) {
             Err(_) if i > 0 => {
                 if start.elapsed().as_millis() > 1 {
@@ -33,16 +35,15 @@ pub fn recv_from(obj: &mut Packets, socket: &UdpSocket) -> Result<usize> {
                 trace!("recv_from err {:?}", e);
                 return Err(e);
             }
-            Ok((size, npkts)) => {
+            Ok((_, npkts)) => {
                 if i == 0 {
                     socket.set_nonblocking(true)?;
                 }
                 trace!("got {} packets", npkts);
                 i += npkts;
-                total_size += size;
                 // Try to batch into big enough buffers
                 // will cause less re-shuffling later on.
-                if start.elapsed().as_millis() > 1 || total_size >= PACKETS_BATCH_SIZE {
+                if start.elapsed().as_millis() > max_wait_ms as u128 || i >= PACKETS_PER_BATCH {
                     break;
                 }
             }
@@ -95,7 +96,7 @@ mod tests {
         }
         send_to(&p, &send_socket).unwrap();
 
-        let recvd = recv_from(&mut p, &recv_socket).unwrap();
+        let recvd = recv_from(&mut p, &recv_socket, 1).unwrap();
 
         assert_eq!(recvd, p.packets.len());
 
@@ -127,4 +128,32 @@ mod tests {
         p2.data[0] = 4;
         assert!(p1 != p2);
     }
+
+    #[test]
+    fn test_packet_resize() {
+        solana_logger::setup();
+        let recv_socket = UdpSocket::bind("127.0.0.1:0").expect("bind");
+        let addr = recv_socket.local_addr().unwrap();
+        let send_socket = UdpSocket::bind("127.0.0.1:0").expect("bind");
+        let mut p = Packets::default();
+        p.packets.resize(PACKETS_PER_BATCH, Packet::default());
+
+        // Should only get PACKETS_PER_BATCH packets per iteration even
+        // if a lot more were sent, and regardless of packet size
+        for _ in 0..2 * PACKETS_PER_BATCH {
+            let mut p = Packets::default();
+            p.packets.resize(1, Packet::default());
+            for m in p.packets.iter_mut() {
+                m.meta.set_addr(&addr);
+                m.meta.size = 1;
+            }
+            send_to(&p, &send_socket).unwrap();
+        }
+
+        let recvd = recv_from(&mut p, &recv_socket, 100).unwrap();
+
+        // Check we only got PACKETS_PER_BATCH packets
+        assert_eq!(recvd, PACKETS_PER_BATCH);
+        assert_eq!(p.packets.capacity(), PACKETS_PER_BATCH);
+    }
 }