archive, cio, cmd, linux: use buffer pools

To avoid buffer bloat in long running processes, we try to use buffer
pools where possible. This is meant to address shim memory usage issues,
but may not be the root cause.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

linux/shim/service_unix.go

@@ -24,7 +24,10 @@ func (p *unixPlatform) CopyConsole(ctx context.Context, console console.Console,
 		cwg.Add(1)
 		go func() {
 			cwg.Done()
-			io.Copy(console, in)
+			p := bufPool.Get().(*[]byte)
+			defer bufPool.Put(p)
+
+			io.CopyBuffer(console, in, *p)
 		}()
 	}
 	outw, err := fifo.OpenFifo(ctx, stdout, syscall.O_WRONLY, 0)
@@ -39,7 +42,10 @@ func (p *unixPlatform) CopyConsole(ctx context.Context, console console.Console,
 	cwg.Add(1)
 	go func() {
 		cwg.Done()
-		io.Copy(outw, console)
+		p := bufPool.Get().(*[]byte)
+		defer bufPool.Put(p)
+
+		io.CopyBuffer(outw, console, *p)
 		console.Close()
 		outr.Close()
 		outw.Close()