On Wed, Mar 13, 2019 at 09:11:13AM +1100, Dave Chinner wrote: > On Tue, Mar 12, 2019 at 03:39:33AM -0700, Ira Weiny wrote: > > IMHO I don't think that the copy_file_range() is going to carry us through the > > next wave of user performance requirements. RDMA, while the first, is not the > > only technology which is looking to have direct access to files. XDP is > > another.[1] > > Sure, all I doing here was demonstrating that people have been > trying to get local direct access to file mappings to DMA directly > into them for a long time. Direct Io games like these are now > largely unnecessary because we now have much better APIs to do > zero-copy data transfer between files (which can do hardware offload > if it is available!). And that is just the file to file case. There are tons of other users of get_user_pages, including various drivers that do large amounts of I/O like video capture. For them it makes tons of sense to transfer directly to/from a mmap()ed file.
