reproduce (this is a W=1 build):
        git checkout 6b5a2b7d9bc156e505f09e698d85d6a1547c1206
        b4 shazam https://lore.kernel.org/r/20260618-erofs-memback-v1-2-5aa7006a241a@redhat.com

        # 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/erofs/