// sysUnused memory region are considered forfeit and the region must not be
// accessed again until sysUsed is called.
func sysUnused(v unsafe.Pointer, n uintptr) {
	gcController.mappedReady.Add(-int64(n))
	sysUnusedOS(v, n)
}

// sysUsed transitions a memory region from Prepared to Ready. It notifies the
// operating system that the memory region is needed and ensures that the region

		if need.size() == 0 {
			continue
		}

		// Map and commit need.
		sysMap(unsafe.Pointer(need.base.addr()), need.size(), p.sysStat)
		sysUsed(unsafe.Pointer(need.base.addr()), need.size(), need.size())
		p.summaryMappedReady += need.size()
	}

	// Update the scavenge index.
	p.summaryMappedReady += p.scav.index.sysGrow(base, limit, p.sysStat)
}

	if reservation == nil {
		throw("failed to reserve page summary memory")
	}
	// There isn't much. Just map it and mark it as used immediately.
	sysMap(reservation, totalSize, p.sysStat)
	sysUsed(reservation, totalSize, totalSize)
	p.summaryMappedReady += totalSize

	// Iterate over the reservation and cut it up into slices.
	//
	// Maintain i as the byte offset from reservation where