On 5/22/22 5:45 AM, Christoph Hellwig wrote: > On Sun, May 22, 2022 at 12:15:59PM +0100, Matthew Wilcox wrote: >>> Direct kernel pointer, surely? And from a quick look, >>> iov_iter_is_kaddr() checks for the wrong value... >> >> Indeed. I didn't test it; it was a quick patch to see if the idea was >> worth pursuing. Neither you nor Christoph thought so at the time, so >> I dropped it. if there are performance improvements to be had from >> doing something like that, it's a more compelling idea than just "Hey, >> this removes a few lines of code and a bit of stack space from every >> caller". > > Oh, right I actually misremembered what the series did. But something > similar except for user pointers might help with the performance issues > that Jens sees, and if it does it might be worth it to avoid having > both the legacy read/write path and the iter path in various drivers. Right, ITER_UADDR or something would useful. I'll try and test that, should be easy to wire up. Agree with Al that it's orthogonal to the miserable kiocb init code, would be nice to get that sorted out too. Al's patch cut 1/3 of the code out of those paths for me. -- Jens Axboe
