reproduce (this is a W=1 build):
        # https://github.com/gestionlin/linux/commit/10c5db9fc7b189b222074598ce5bc9c1d8cd0ea8
        git remote add linyunsheng https://github.com/gestionlin/linux.git
        git fetch --no-tags linyunsheng page_bulk_alloc_opt_v2
        git checkout 10c5db9fc7b189b222074598ce5bc9c1d8cd0ea8
        # 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 fs/btrfs/