for l, shift := range levelShift {
		entries := 1 << (heapAddrBits - shift)

		// Put this reservation into a slice.
		sl := notInHeapSlice{(*notInHeap)(reservation), 0, entries}
		p.summary[l] = *(*[]pallocSum)(unsafe.Pointer(&sl))

		reservation = add(reservation, uintptr(entries)*pallocSumBytes)
	}
}

// See mpagealloc_64bit.go for details.
func (p *pageAlloc) sysGrow(base, limit uintptr) {

		r := sysReserve(nil, b)
		if r == nil {
			throw("failed to reserve page summary memory")
		}

		// Put this reservation into a slice.
		sl := notInHeapSlice{(*notInHeap)(r), 0, entries}
		p.summary[l] = *(*[]pallocSum)(unsafe.Pointer(&sl))
	}
}

// sysGrow performs architecture-dependent operations on heap
// growth for the page allocator, such as mapping in new memory
// for summaries. It also updates the length of the slices in