If you use patched openmode you can just edit /etc/init/enable-swap.conf and be done with it. No additional steps needed.

If you have incepted device and are unsure about following Rainisto's step by step instruction you probably shouldn't even try it. (or atleast be aware that one typo or logging out of shell between the steps is very likely to malf your N9 and require a reflash.) Similarly if you don't have a clear idea why you are doing this, (no it won't speed up things noticeably/at all unless you have something already hogging up most of your RAM.) then don't do it.