On Thu, May 27, 2021 at 09:04:24AM +0100, Christoph Hellwig wrote: > On Wed, May 26, 2021 at 09:07:41AM +0100, Mel Gorman wrote: > > + !defined(CONFIG_DEBUG_LOCK_ALLOC) && \ > > + !defined(CONFIG_PAHOLE_HAS_ZEROSIZE_PERCPU_SUPPORT) > > + /* > > + * pahole 1.21 and earlier gets confused by zero-sized per-CPU > > + * variables and produces invalid BTF. Ensure that > > + * sizeof(struct pagesets) != 0 for older versions of pahole. > > + */ > > + char __pahole_hack; > > + #warning "pahole too old to support zero-sized struct pagesets" > > +#endif > > Err, hell no. We should not mess up the kernel for broken tools that > are not relevant to the kernel build itself ever. 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. The second alternative fix is to embed the local_lock within struct per_cpu_pages. It was shown this was possible in https://lore.kernel.org/linux-rt-users/20210419141341.26047-1-mgorman@xxxxxxxxxxxxxxxxxxx/T/#md1001d7af52ac0d6d214b95e98fe051f9399de64 but I dropped it because it makes the locking protocol complex e.g. config-specific lock-switchin in free_unref_page_list. The last one is wrapping local_lock behind #defines and only defining the per-cpu structures when local_lock_t is a non-zero size. That is simply too ugly for words, the locking patterns should always be the same. -- Mel Gorman SUSE Labs
