On 09/07/2020 16:26, Christoph Hellwig wrote: > On Thu, Jul 09, 2020 at 12:10:36PM +0100, Matthew Wilcox wrote: >> On Thu, Jul 09, 2020 at 11:17:05AM +0100, Christoph Hellwig wrote: >>> I really don't like this series at all. If saves a single pointer >>> but introduces a complicated machinery that just doesn't follow any >>> natural flow. And there doesn't seem to be any good reason for it to >>> start with. >> >> Jens doesn't want the kiocb to grow beyond a single cacheline, and we >> want the ability to set the loff_t in userspace for an appending write, >> so the plan was to replace the ki_complete member in kiocb with an >> loff_t __user *ki_posp. >> >> I don't think it's worth worrying about growing kiocb, personally, >> but this seemed like the easiest way to make room for a new pointer. > > The user offset pointer has absolutely no business in the the kiocb > itself - it is a io_uring concept which needs to go into the io_kiocb, > which has 14 bytes left in the last cache line in my build. It would > fit in very well there right next to the result and user pointer. After getting a valid offset, io_uring shouldn't do anything but complete the request. And as io_kiocb implicitly contains a CQE entry, not sure we need @append_offset in the first place. Kanchan, could you take a look if you can hide it in req->cflags? -- Pavel Begunkov
