Re: [RFC] mmap(MAP_CONTIG)

From: Mike Kravetz
Date: Wed Oct 04 2017 - 13:09:21 EST

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 dÃjà vu. Wasnât 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.

Mike Kravetz