Re: [RFC PATCH 0/5] Support DEVICE_GENERIC memory in migrate_vma_*

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, May 27, 2021 at 07:08:04PM -0400, Felix Kuehling wrote:
> Now we're trying to migrate data to and from that memory using the
> migrate_vma_* helpers so we can support page-based migration in our
> unified memory allocations, while also supporting CPU access to those
> pages.

So you have completely coherent and indistinguishable GPU and CPU
memory and the need of migration is basicaly alot like NUMA policy
choice - get better access locality?
 
> This patch series makes a few changes to make MEMORY_DEVICE_GENERIC pages
> behave correctly in the migrate_vma_* helpers. We are looking for feedback
> about this approach. If we're close, what's needed to make our patches
> acceptable upstream? If we're not close, any suggestions how else to
> achieve what we are trying to do (i.e. page migration and coherent CPU
> access to VRAM)?

I'm not an expert in migrate, but it doesn't look outrageous.

Have you thought about allowing MEMORY_DEVICE_GENERIC to work with
hmm_range_fault() so you can have nice uniform RDMA?

People have wanted to do that with MEMORY_DEVICE_PRIVATE but nobody
finished the work

Jason