On Mon, Oct 19, 2020 at 01:29:42PM +0100, Tvrtko Ursulin wrote: > > On 19/10/2020 13:12, Jason Gunthorpe wrote: > > On Mon, Oct 19, 2020 at 10:50:14AM +0100, Tvrtko Ursulin wrote: > > > > overshoot the max_segment if it is not a multiple of PAGE_SIZE. Simply fix > > > > the alignment before starting and don't expose this implementation detail > > > > to the callers. > > > > > > What does not make complete sense to me is the statement that input > > > alignment requirement makes it impossible to connect to DMA layer, but then > > > the patch goes to align behind the covers anyway. > > > > > > At minimum the kerneldoc should explain that max_segment will still be > > > rounded down. But wouldn't it be better for the API to be more explicit and > > > just require aligned anyway? > > > > Why? > > > > The API is to not produce sge's with a length longer than max_segment, > > it isn't to produce sge's of exactly max_segment. > > > > Everything else is an internal detail > > (Half-)pretending it is disconnected from PAGE_SIZE, when it really isn't, > isn't the most obvious API design in my view. It is not information the callers need to care about > In other words, if you let users pass in 4097 and it just works by rounding > down to 4096, but you don't let them pass 4095, I just find this odd. That is also an implementation detail, there is nothing preventing smaller than page size other than complexity of implementing the algorithm. If something ever needed it, it could be done. > My question was why not have callers pass in page aligned max segment like > today which makes it completely transparent. Why put this confusing code in every caller? Especially for something a driver is supposed to call. Will just make bugs Jason
