On Thu, Jul 31, 2025 at 12:44:09AM +0800, alexjlzheng@xxxxxxxxx wrote: > From: Jinliang Zheng <alexjlzheng@xxxxxxxxxxx> > > Prefaulting the write source buffer incurs an extra userspace access > in the common fast path. Make iomap_write_iter() consistent with > generic_perform_write(): only touch userspace an extra time when > copy_folio_from_iter_atomic() has failed to make progress. This is probably a good thing to have, but I'm curous if you did see it making a different for workloads? > + /* > + * Faults here on mmap()s can recurse into arbitrary > + * filesystem code. Lots of locks are held that can > + * deadlock. Use an atomic copy to avoid deadlocking > + * in page fault handling. We can and should use all 80 characters in a line for comments. > + /* > + * 'folio' is now unlocked and faults on it can be > + * handled. Ensure forward progress by trying to > + * fault it in now. > + */ Same here. I really wish we could find a way to share the core write loop between at least iomap and generic_perform_write and maybe also the other copy and pasters. But that's for another time..
