func (n *Node) usesMM() bool {
	return (n.level & mmFlag) != 0
}
this is inlined by go as seen from profile
package skiplist
import (
	"reflect"
	"sync/atomic"
	"unsafe"
)
const deletedFlag = uint64(1) << 52
const deletedFlagMask = ^deletedFlag
const mmFlag = int(1) << 62
const mmFlagMask = (^mmFlag)
var nodeHdrSizeMM = unsafe.Sizeof(NodeMM{})
var nodeRefSizeMM = unsafe.Sizeof(NodeRefMM{})
type Node struct {
	level int  
	itm   unsafe.Pointer
	Link  unsafe.Pointer
	Cache int64           
	next  unsafe.Pointer  
}
type NodeRef struct {
	deleted bool
	ptr     *Node
}
type NodeMM struct {
	level int  
	itm   unsafe.Pointer
	Link  unsafe.Pointer
	Cache int64  
}
type NodeRefMM struct {
	tagptr uint64
}
func (n *Node) setMM() {
	n.level |= mmFlag
}