Re: [HMM 03/15] mm/unaddressable-memory: new type of ZONE_DEVICE for unaddressable memory

[Jon Masters]

On 04/23/2017 08:39 PM, John Hubbard wrote:

> Actually, MEMORY_DEVICE_PRIVATE / _PUBLIC seems like a good choice to 
> me, because the memory may not remain CPU-unaddressable in the future. 
> By that, I mean that I know of at least one company (ours) that is 
> working on products that will support hardware-based memory coherence 
> (and access counters to go along with that). If someone were to enable 
> HMM on such a system, then the device memory would be, in fact, directly 
> addressable by a CPU--thus exactly contradicting the "unaddressable" name.

I'm expecting similar with CCIX-like coherently attached accelerators
running within FPGAs and as discrete devices as well. Everyone and their
dog is working on hardware based coherence as a programming convenience
and so the notion of ZONE_DEVICE as it stood is going to rapidly evolve
over the next 18 months, maybe less. Short term anyway.

Jon.