func (l *sweepLocker) tryAcquire(s *mspan) (sweepLocked, bool) {
	if !l.valid {
		throw("use of invalid sweepLocker")
	}
	// Check before attempting to CAS.
	if atomic.Load(&s.sweepgen) != l.sweepGen-2 {
		return sweepLocked{}, false
	}
	// Attempt to acquire sweep ownership of s.
	if !atomic.Cas(&s.sweepgen, l.sweepGen-2, l.sweepGen-1) {
		return sweepLocked{}, false
	}

	if stale {
		// It's stale, so just sweep it. Sweeping will put it on
		// the right list.
		//
		// We don't use a sweepLocker here. Stale cached spans
		// aren't in the global sweep lists, so mark termination
		// itself holds up sweep completion until all mcaches
		// have been swept.
		ss := sweepLocked{s}
		ss.sweep(false)
	} else {
		if int(s.nelems)-int(s.allocCount) > 0 {
			// Put it back on the partial swept list.

	// those spans have been forced out.
	//
	// If gcSweep fully swept the heap (for example if the sweep
	// is not concurrent due to a GODEBUG setting), then we expect
	// the sweepLocker to be invalid, since sweeping is done.
	//
	// N.B. Below we might duplicate some work from gcSweep; this is
	// fine as all that work is idempotent within a GC cycle, and

String id=202
	data="/usr/local/google/home/mknyszek/work/go-1/src/runtime/trace2runtime.go"
String id=203
	data="runtime.traceLocker.GCSweepSpan"
String id=204
	data="runtime.(*sweepLocked).sweep"
String id=205
	data="net.(*netFD).Write"
String id=206
	data="net.(*conn).Write"
String id=207
	data="runtime.(*traceAdvancerState).start"
String id=208

	data="runtime.gcStart"
String id=51
	data="runtime.traceLocker.GCSweepSpan"
String id=52
	data="/usr/local/google/home/mknyszek/work/go-1/src/runtime/trace2runtime.go"
String id=53
	data="runtime.(*sweepLocked).sweep"
String id=54
	data="/usr/local/google/home/mknyszek/work/go-1/src/runtime/mgcsweep.go"
String id=55
	data="runtime.(*mcentral).cacheSpan"
String id=56