Re: [LSF/MM/BPF TOPIC] The future of ZONE_DEVICE pages

[Leon Romanovsky <leon@kernel.org>]

On Fri, Jan 31, 2025 at 10:52:37AM -0400, Jason Gunthorpe wrote:
> On Fri, Jan 31, 2025 at 01:59:09PM +1100, Alistair Popple wrote:
> > Combining P2PDMA and DEVICE_PRIVATE pages
> > =========================================
> > 
> > Currently device memory that cannot be directly accessed via the CPU can be
> > represented by DEVICE_PRIVATE pages allowing it to be mapped and treated like
> > a normal virtual page by userpsace. Many devices also support accessing device
> > memory directly from the CPU via a PCIe BAR.
> > 
> > This access requires a P2PDMA page, meaning there are potentially two pages
> > tracking the same piece of physical memory. This not only seems wasteful but
> > fraught - for example device drivers need to keep page lifetimes in sync. I
> > would like to discuss ways of solving this.
> 
> My general plan for this has been to teach the DMA API how to do P2P
> without struct page. Leon's topic is the frist step on this journey.
>   https://lore.kernel.org/linux-mm/97f385db-42c9-4c04-8fba-9b1ba8ffc525@nvidia.com/

The latest proposal for LSF/MM 2025 is here:
[LSF/MM/BPF TOPIC] DMA mapping API in complex scenarios
https://lore.kernel.org/linux-rdma/20250122071600.GC10702@unreal/T/#u

Thanks