Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> writes: > On Fri, Aug 26, 2022 at 11:54 AM Stephen Brennan > <stephen.s.brennan@xxxxxxxxxx> wrote: [...] >> Future Work >> ----------- >> >> If this proves acceptable, I'd like to follow-up with a kernel patch to >> add a configuration option (default=n) for generating BTF with all >> variables, which distributions could choose to enable or not. >> >> There was previous discussion[3] about leveraging split BTF or building >> additional kernel modules to contain the extra variables. I believe with >> this patch series, it is possible to do that. However, I'd argue that >> simpler is better here: the advantage for using BTF is having it all >> available in the kernel/module image. Storing extra BTF on the >> filesystem would break that advantage, and at that point, you'd be >> better off using a debuginfo format like CTF, which is lightweight and >> expected to be found on the filesystem. > > With all or nothing approach the distros would have a hard choice > to make whether to enable that kconfig, increase BTF and consume > extra memory without any obvious reason or just don't do it. > Majority probably is not going to enable it. > So the feature will become a single vendor only and with > inevitable bit-rot. I'd intend to support it even if just a single distribution enabled it. But I do see your concern. > Whereas with split BTF and extra kernel module approach > we can enable BTF with all global vars by default. > The extra module will be shipped by all distros and tools > like bpftrace might start using it. Split BTF is currently limited to a single base BTF file. We'd need more patches for pahole to support multiple --btf_base files: e.g. vmlinux.btf and vmlinux-variables.btf. There's also the question of modules: presumably we wouldn't try to have "$MODULE" and "$MODULE-btf-extra" modules due to the added complexity. I doubt the space savings would be worth it. I can look into these concerns, but if possible I would like to proceed with this series, as it is a separate concern from the exact mechanism by which we include extra BTF into the kernel. Thanks, Stephen
