On Mon, Jun 06, 2022 at 12:41:06PM -0700, Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote: > I don't know if there is a standard way to handle this, but I think > you should know the configs of your kernel when you are loading a bpf > program? Isn't this one of purposes of BTF? (I don't know, I'm genuinely asking.) > If the CONFIG_CGROUPS=1 but CONFIG_MEMCG=0 I think everything will > work normally except that task_memcg() will always return NULL so no > stats will be collected, which makes sense. I was not able to track down what is the include chain to tools/testing/selftests/bpf/progs/cgroup_vmscan.c, i.e. how is the enum value memory_cgrp_id defined. (A custom kernel module build requires target kernel's header files, I could understand that compiling a BPF program requires them likewise and that's how this could work. Although, it goes against my undestanding of the CO-RE principle.) > There will be some overhead to running bpf programs that will always > do nothing, but I would argue that it's the userspace's fault here for > loading bpf programs on a non-compatible kernel. Yeah, running an empty program is non-issue in my eyes, I was rather considering whether the program uses proper offsets. Michal
