Re: [RFC 0/4] RFC - Coherent Device Memory (Not for inclusion)

[John Hubbard <jhubbard@nvidia.com>]

On 05/01/2017 04:51 PM, Reza Arbab wrote:
> On Mon, May 01, 2017 at 02:56:34PM -0700, John Hubbard wrote:
>> On 05/01/2017 02:04 PM, Reza Arbab wrote:
>>> On Mon, May 01, 2017 at 01:41:55PM -0700, John Hubbard wrote:
>>>> 1. A way to move pages between NUMA nodes, both virtual address and physical 
>>>> address-based, from kernel mode.
>>>
>>> Jérôme's migrate_vma() and migrate_dma() should have this covered, including 
>>> DMA-accelerated copy.
>>
>> Yes, that's good. I wasn't sure from this discussion here if either or both of 
>> those would be used, but now I see.
>>
>> Are those APIs ready for moving pages between NUMA nodes? As there is no NUMA node 
>> id in the API, are we relying on the pages' membership (using each page and 
>> updating which node it is on)?
> 
> Yes. Those APIs work by callback. The alloc_and_copy() function you provide will be 
> called at the appropriate point in the migration. Yours would allocate from a 
> specific destination node, and copy using DMA.
> 

hmmm, that reminds me: the whole story of "which device is this, and which NUMA node 
does it correlate to?" will have to be wired up. That is *probably* all in the 
device driver, but since I haven't worked through it, I'd be inclined to list it as 
an item on the checklist, just in case it requires some little hook in the upstream 
kernel.

thanks,
john h

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