On Tue, Oct 22, 2019 at 05:41:11PM +0000, Jason Gunthorpe wrote: > On Tue, Oct 22, 2019 at 01:30:26PM -0400, Jerome Glisse wrote: > > > > Smart drivers can test somehow for pfn == zero_page and optimize? > > > > There is nothing to optimize here, i do not know any hardware that > > have a special page table entry that make all memory access return > > zero. > > Presumably any GPU could globally dedicate one page of internal memory > as a zero page and remap CPU zero page to that internal memory page? > This is basically how the CPU zero page works. Yes that would work too but i do not know of any upstream driver that does that. > I suspect mlx5 could do the same with its internal memory, but the > internal memory is too limited to make this worth while. > > mlx5 also has a specially 'zero MR' that always reads as zero (and > discards writes), but it doesn't quite fit well into the ODP flow. Well you can always ask for new stuff to your beloved hardware engineers, they never say no right ? :) Cheers, Jérôme
