// allocation if the budget runs low.
	spanBudget := 100

	var s *mspan
	var sl sweepLocker

	// Try partial swept spans first.
	sg := mheap_.sweepgen
	if s = c.partialSwept(sg).pop(); s != nil {
		goto havespan
	}

	sl = sweep.active.begin()
	if sl.valid {
		// Now try partial unswept spans.
		for ; spanBudget >= 0; spanBudget-- {
			s = c.partialUnswept(sg).pop()
			if s == nil {