portlist: reduce allocs on Linux

Notably, it no longer allocates proportional to the number of open
sockets on the machine. Any alloc reduction numbers are a little
contrived with such a reduction but e.g. on a machine with 50,000
connections open:

name          old time/op    new time/op    delta
ParsePorts-6    57.7ms ± 6%    32.8ms ± 3%   -43.04%  (p=0.000 n=9+10)

name          old alloc/op   new alloc/op   delta
ParsePorts-6    24.0MB ± 0%     0.0MB ± 0%  -100.00%  (p=0.000 n=10+9)

name          old allocs/op  new allocs/op  delta
ParsePorts-6      100k ± 0%        0k ± 0%   -99.99%  (p=0.000 n=10+10)

Updates tailscale/corp#2566

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

portlist/portlist_linux.go

@@ -17,6 +17,7 @@
 	"syscall"
 	"time"
 
+	"go4.org/mem"
 	"golang.org/x/sys/unix"
 	"tailscale.com/syncs"
 )
@@ -82,8 +83,11 @@ func parsePorts(r *bufio.Reader, proto string) ([]Port, error) {
 		return nil, err
 	}
 
+	fields := make([]mem.RO, 0, 20) // 17 current fields + some future slop
+
+	var inoBuf []byte
 	for err == nil {
-		line, err := r.ReadString('\n')
+		line, err := r.ReadSlice('\n')
 		if err == io.EOF {
 			break
 		}
@@ -92,37 +96,39 @@ func parsePorts(r *bufio.Reader, proto string) ([]Port, error) {
 		}
 
 		// sl local rem ... inode
-		words := strings.Fields(line)
+		fields = mem.AppendFields(fields[:0], mem.B(line))
-		local := words[1]
+		local := fields[1]
-		rem := words[2]
+		rem := fields[2]
-		inode := words[9]
+		inode := fields[9]
 
 		// If a port is bound to localhost, ignore it.
 		// TODO: localhost is bigger than 1 IP, we need to ignore
 		// more things.
-		if strings.HasPrefix(local, v4Localhost) || strings.HasPrefix(local, v6Localhost) {
+		if mem.HasPrefix(local, mem.S(v4Localhost)) || mem.HasPrefix(local, mem.S(v6Localhost)) {
 			continue
 		}
-		if rem != v4Any && rem != v6Any {
+		if !rem.Equal(mem.S(v4Any)) && !rem.Equal(mem.S(v6Any)) {
 			// not a "listener" port
 			continue
 		}
 
 		// Don't use strings.Split here, because it causes
 		// allocations significant enough to show up in profiles.
-		i := strings.IndexByte(local, ':')
+		i := mem.IndexByte(local, ':')
 		if i == -1 {
-			return nil, fmt.Errorf("%q unexpectedly didn't have a colon", local)
+			return nil, fmt.Errorf("%q unexpectedly didn't have a colon", local.StringCopy())
 		}
-		portv, err := strconv.ParseUint(local[i+1:], 16, 16)
+		portv, err := mem.ParseUint(local.SliceFrom(i+1), 16, 16)
 		if err != nil {
-			return nil, fmt.Errorf("%#v: %s", local[9:], err)
+			return nil, fmt.Errorf("%#v: %s", local.SliceFrom(9).StringCopy(), err)
 		}
-		inodev := fmt.Sprintf("socket:[%s]", inode)
+		inoBuf = append(inoBuf[:0], "socket:["...)
+		inoBuf = mem.Append(inoBuf, inode)
+		inoBuf = append(inoBuf, ']')
 		ret = append(ret, Port{
 			Proto: proto,
 			Port:  uint16(portv),
-			inode: inodev,
+			inode: string(inoBuf),
 		})
 	}
 

portlist/portlist_linux_test.go

@@ -7,6 +7,7 @@
 import (
 	"bufio"
 	"bytes"
+	"io"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -65,3 +66,37 @@ func TestParsePorts(t *testing.T) {
 		})
 	}
 }
+
+func BenchmarkParsePorts(b *testing.B) {
+	b.ReportAllocs()
+
+	var contents bytes.Buffer
+	contents.WriteString(`  sl  local_address                         remote_address                        st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode
+   0: 00000000000000000000000001000000:0277 00000000000000000000000000000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 35720 1 0000000000000000 100 0 0 10 0
+   1: 00000000000000000000000000000000:1F91 00000000000000000000000000000000:0000 0A 00000000:00000000 00:00000000 00000000  1000        0 142240557 1 0000000000000000 100 0 0 10 0
+   2: 00000000000000000000000000000000:0016 00000000000000000000000000000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 34064 1 0000000000000000 100 0 0 10 0
+`)
+	for i := 0; i < 50000; i++ {
+		contents.WriteString("   3: 69050120005716BC64906EBE009ECD4D:D506 0047062600000000000000006E171268:01BB 01 00000000:00000000 02:0000009E 00000000  1000        0 151042856 2 0000000000000000 21 4 28 10 -1\n")
+	}
+
+	want := []Port{
+		{Proto: "tcp", Port: 8081, inode: "socket:[142240557]"},
+		{Proto: "tcp", Port: 22, inode: "socket:[34064]"},
+	}
+
+	r := bytes.NewReader(contents.Bytes())
+	br := bufio.NewReader(&contents)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		r.Seek(0, io.SeekStart)
+		br.Reset(r)
+		got, err := parsePorts(br, "tcp")
+		if err != nil {
+			b.Fatal(err)
+		}
+		if len(got) != 2 || got[0].Port != 8081 || got[1].Port != 22 {
+			b.Fatalf("wrong result:\n got %+v\nwant %+v", got, want)
+		}
+	}
+}