reproduce (this is a W=1 build):
        git remote add willy-pagecache git://git.infradead.org/users/willy/pagecache
        git fetch --no-tags willy-pagecache shrunk-page
        git checkout b19fdb3a0ac16a88851e63449dfeedb21aee7c19
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash mm/