reproduce (this is a W=1 build):
        # https://github.com/davidhildenbrand/linux/commit/17725734e525b4cc4ae1f26107e45c0ca19c17a6
        git remote add davidhildenbrand https://github.com/davidhildenbrand/linux
        git fetch --no-tags davidhildenbrand pfn_cow
        git checkout 17725734e525b4cc4ae1f26107e45c0ca19c17a6
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash arch/x86/mm/pat/