On Thu, May 27, 2021 at 7:37 AM Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > On Thu, May 27, 2021 at 2:19 AM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > > > On Thu, May 27, 2021 at 10:04:22AM +0100, Mel Gorman wrote: > > > What do you suggest as an alternative? > > > > > > I added Arnaldo to the cc as he tagged the last released version of > > > pahole (1.21) and may be able to tag a 1.22 with Andrii's fix for pahole > > > included. > > > > > > The most obvious alternative fix for this issue is to require pahole > > > 1.22 to set CONFIG_DEBUG_INFO_BTF but obviously a version 1.22 that works > > > needs to exist first and right now it does not. I'd be ok with this but > > > users of DEBUG_INFO_BTF may object given that it'll be impossible to set > > > the option until there is a release. > > > > Yes, disable BTF. Empty structs are a very useful feature that we use > > in various places in the kernel. We can't just keep piling hacks over > > hacks to make that work with a recent fringe feature. Sorry, I accidentally send out empty response. CONFIG_DEBUG_INFO_BTF is a crucial piece of modern BPF ecosystem. It is enabled by default by most popular Linux distros. So it's hardly a fringe feature and is something that many people and applications depend on. I agree that empty structs are useful, but here we are talking about per-CPU variables only, which is the first use case so far, as far as I can see. If we had pahole 1.22 released and widely packaged it could have been a viable option to force it on everyone. But right now that's not the case. So while ugly, making sure pagesets is non-zero-sized is going to avoid a lot of pain for a lot of people. By the time we need another zero-sized per-CPU var, we might be able to force pahole to 1.22.
