[caf]

Code that is loaded into memory stays in memory when three is no swap.

That is not true. In the normal case (absent debugging, JIT, self-modifying code etc), pages of executable code are clean, shared mappings so they do not interact with swap at all.

As clean, shared mappings they are eligible to be dropped from the page cache in the same way as other clean file mapped pages.

(Your executable code pages essentially are mmapped files. )