reproduce:
        git remote add akpm-mm https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git
        git fetch akpm-mm mm-everything
        git checkout akpm-mm/mm-everything
        b4 shazam https://lore.kernel.org/r/20231108065818.19932-5-link@vivo.com
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs