freeRetainedMetadata

        fn freeRetainedMetadata(self: *Self) void {
            comptime assert(config.retain_metadata);
            if (config.never_unmap) {
                // free large allocations that were intentionally leaked by never_unmap
                var it = self.large_allocations.iterator();
                while (it.next()) |large| {
                    if (large.value_ptr.freed) {
                        self.backing_allocator.rawFree(large.value_ptr.bytes, large.value_ptr.alignment, @returnAddress());
                    }
                }
            }
        }