// Consume these 3 hints and force the runtime to find some
	// fallback hints.
	for i := 0; i < 5; i++ {
		// Reserve memory at the next hint so it can't be used
		// for the heap.
		start, end, ok := MapNextArenaHint()
		if !ok {
			t.Skipf("failed to reserve memory at next arena hint [%#x, %#x)", start, end)
		}
		t.Logf("reserved [%#x, %#x)", start, end)
		disallowed = append(disallowed, [2]uintptr{start, end})

			return
		}
	}
	hint.next = nil
}

// MapNextArenaHint reserves a page at the next arena growth hint,
// preventing the arena from growing there, and returns the range of
// addresses that are no longer viable.
//
// This may fail to reserve memory. If it fails, it still returns the
// address range it attempted to reserve.
func MapNextArenaHint() (start, end uintptr, ok bool) {
	hint := mheap_.arenaHints