Re: [RFC] mmap(MAP_CONTIG)

On 10/04/2017 10:08 AM, Mike Kravetz wrote:

On 10/04/2017 04:54 AM, Michal Nazarewicz wrote:

quoted

On Tue, Oct 03 2017, Mike Kravetz wrote:

quoted

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

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>