}

// GCSweepStart prepares to trace a sweep loop. This does not
// emit any events until traceGCSweepSpan is called.
//
// GCSweepStart must be paired with traceGCSweepDone and there
// must be no preemption points between these two calls.
//
// Must be called with a valid P.
func (tl traceLocker) GCSweepStart() {
	// Delay the actual GCSweepBegin event until the first span

	spanBytes := uintptr(class_to_allocnpages[c.spanclass.sizeclass()]) * _PageSize
	deductSweepCredit(spanBytes, 0)

	traceDone := false
	trace := traceAcquire()
	if trace.ok() {
		trace.GCSweepStart()
		traceRelease(trace)
	}

	// If we sweep spanBudget spans without finding any free
	// space, just allocate a fresh span. This limits the amount
	// of time we can spend trying to find free space and

	if mheap_.sweepPagesPerByte == 0 {
		// Proportional sweep is done or disabled.
		return
	}

	trace := traceAcquire()
	if trace.ok() {
		trace.GCSweepStart()
		traceRelease(trace)
	}

	// Fix debt if necessary.
retry:
	sweptBasis := mheap_.pagesSweptBasis.Load()
	live := gcController.heapLive.Load()
	liveBasis := mheap_.sweepHeapLiveBasis

	EvSTWStart:          {"GCSTWStart", 5, false, []string{"kindid"}, []string{"kind"}}, // <= 1.9, args was {} (implicitly {0})
	EvSTWDone:           {"GCSTWDone", 5, false, []string{}, nil},
	EvGCSweepStart:      {"GCSweepStart", 5, true, []string{}, nil},
	EvGCSweepDone:       {"GCSweepDone", 5, false, []string{"swept", "reclaimed"}, nil}, // before 1.9, format was {}
	EvGoCreate:          {"GoCreate", 5, true, []string{"g", "stack"}, nil},

	// sweeping, so we can read h.sweepArenas, and so
	// traceGCSweepStart/Done pair on the P.
	mp := acquirem()

	trace := traceAcquire()
	if trace.ok() {
		trace.GCSweepStart()
		traceRelease(trace)
	}

	arenas := h.sweepArenas
	locked := false
	for npage > 0 {
		// Pull from accumulated credit first.
		if credit := h.reclaimCredit.Load(); credit > 0 {
			take := credit