Re: [PATCH 0/2] Remove kiocb ki_complete

[Christoph Hellwig <hch@infradead.org>]

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.