On 10/04/2017 10:08 AM, Mike Kravetz wrote: > On 10/04/2017 04:54 AM, Michal Nazarewicz wrote: >> On Tue, Oct 03 2017, Mike Kravetz wrote: >>> At Plumbers this year, Guy Shattah and Christoph Lameter gave a presentation >>> titled 'User space contiguous memory allocation for DMA' [1]. The slides >>> point out the performance benefits of devices that can take advantage of >>> larger physically contiguous areas. >> >> Issue I have is that kind of memory needed may depend on a device. Some >> may require contiguous blocks. Some may support scatter-gather. Some >> may be behind IO-MMU and not care either way. >> >> Furthermore, I feel déjà vu. Wasn’t dmabuf supposed to address this >> issue? > > Thanks Michal, > > I was unaware of dmabuf and am just now looking at capabilities. The > question is whether or not the IB driver writers requesting mmap(MAP_CONTIG) > functionality could make use of dmabuf. That is out of my are of expertise, > so I will let them reply. >
I don't think dmabuf as it exists today would help anything here. It's designed to share buffers via fd but you still need some place/driver to actually get the allocation and then export it since there isn't a single interface for allocations. You could convert drivers to take a dma_buf fd if there were appropriate buffers available though. Thanks, Laura
