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>

cmd/ctr/commands/shim/io_unix.go

@@ -12,6 +12,13 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+var bufPool = sync.Pool{
+	New: func() interface{} {
+		buffer := make([]byte, 32<<10)
+		return &buffer
+	},
+}
+
 func prepareStdio(stdin, stdout, stderr string, console bool) (wg *sync.WaitGroup, err error) {
 	wg = &sync.WaitGroup{}
 	ctx := gocontext.Background()
@@ -26,7 +33,9 @@ func prepareStdio(stdin, stdout, stderr string, console bool) (wg *sync.WaitGrou
 		}
 	}(f)
 	go func(w io.WriteCloser) {
-		io.Copy(w, os.Stdin)
+		p := bufPool.Get().(*[]byte)
+		defer bufPool.Put(p)
+		io.CopyBuffer(w, os.Stdin, *p)
 		w.Close()
 	}(f)