type gcControllerState struct {
	// heapLive is the number of bytes considered live by the GC.
	// That is: retained by the most recent GC plus allocated
	// since then. heapLive ≤ memstats.totalAlloc-memstats.totalFree, since
	// heapAlloc includes unmarked objects that have not yet been swept (and
	// hence goes up as we allocate and down as we sweep) while heapLive
	// excludes these objects (and hence only goes up between GCs).
	//
	// To reduce contention, this is updated only when obtaining a span
	// from an mcentral and at this point it counts all of the unallocated
	// slots in that span (which will be allocated before that mcache
	// obtains another span from that mcentral). Hence, it slightly
	// overestimates the "true" live heap size. It's better to overestimate
	// than to underestimate because 1) this triggers the GC earlier than
	// necessary rather than potentially too late and 2) this leads to a
	// conservative GC rate rather than a GC rate that is potentially too
	// low.
	//
	// Whenever this is updated, call traceHeapAlloc() and
	// this gcControllerState's revise() method.
	heapLive atomic.Uint64

	// heapMarked is the number of bytes marked by the previous
	// GC. After mark termination, heapLive == heapMarked, but
	// unlike heapLive, heapMarked does not change until the
	// next mark termination.
	heapMarked uint64
}