[aidenn0]

To be fair, I said "approximately" The cost of a nursery GC in SBCL is O(n+m) where n is the number of live objects in the nursery and m is the number of GC roots. If this code is all you are running then n will be 1, so it's just scanning the roots, which only happens when you have allocated enough integers to fill the nursery, so gets amortized across thousands of loop iterations.