On Tue, Sep 10, 2024 at 12:48:16PM +0200, Mateusz Guzik wrote: > May I suggest adding a compile-time assert on the size? While it may be > growing it will be unavoidable at some point, it at least wont happen > unintentionally. That should be fine for this structure since everything is defined in terms of types that should be fixed across architectures, and they aren't using any types that might change depending on the kernel config, but as a general matter, we should be a bit careful when rearranging structrues to avoid holes and to keep things on the same cache line. I recently had a patch submission which was rearranging structure order for an ext4 data structure, and what worked for the patch submitter didn't work for me, because of differences between kernel configs and/or architecture types. So it's been on my todo list to do a sanity check of various ext4 structuers, but to do so checking a number of different architectures and common production kernel configs (I don't really care if enabling lockdep results in more holes, because performance is going to be impacted way more for reasons other than cache lines :-). Hmm, maybe fodder for a GSOC or intern project would be creating some kind of automation to check for optimal structure layouts across multiple configs/architectures? - Ted
