}
	if s != &emptymspan {
		// Mark this span as no longer cached.
		if s.sweepgen != mheap_.sweepgen+3 {
			throw("bad sweepgen in refill")
		}
		mheap_.central[spc].mcentral.uncacheSpan(s)

		// Count up how many slots were used and record it.
		stats := memstats.heapStats.acquire()
		slotsUsed := int64(s.allocCount) - int64(s.allocCountBeforeCache)

	s.allocCache >>= s.freeindex % 64

	return s
}

// Return span from an mcache.
//
// s must have a span class corresponding to this
// mcentral and it must not be empty.
func (c *mcentral) uncacheSpan(s *mspan) {
	if s.allocCount == 0 {
		throw("uncaching span but s.allocCount == 0")
	}

	sg := mheap_.sweepgen
	stale := s.sweepgen == sg+1

	// Fix up sweepgen.
	if stale {