Looks OK, but I’d request some related additional cleanup.
Also, I’d appreciate an example of the generated code for passing `page_id_t` by value on i386, amd64, aarch64. (I would like to confirm that it is only one 64-bit register or two 32-bit registers.)
amd64: really passed in one `rdi` https://godbolt.org/z/YBAX0e
i686: passed in a stack. And I don't know why https://godbolt.org/z/AZ3L9H
aarch64: I don't know assembly. It looks like a struct was passed on a stack https://godbolt.org/z/q1ucnG
Cleanup done, PR updated.
Thank you! I merged this along with some further cleanup.
kevg
>aarch64: I don't know assembly. It looks like a struct was passed on a stack https://godbolt.org/z/q1ucnG
Because it was 32-bit arm 
In 10.5, page_id_t was optimized further to be a wrapper of a single 64-bit integer, so that we can simplify comparisons.