Re: [RFC summary] Enable Coherent Device Memory

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2017-05-17 at 08:54 -0500, Christoph Lameter wrote:
> You can provide a library that does it?
> 
> > The base idea behind the counters we have on the link is for the HW to
> > know when memory is accessed "remotely", so that the device driver can
> > make decision about migrating pages into or away from the device,
> > especially so that applications don't have to concern themselves with
> > memory placement.
> 
> Library can enquire about the current placement of the pages and move them
> if necessary?

No, doing that from a library would not work. It should be done by the
driver, but that's not a problem in the proposed scheme and doesn't
require new MM hooks afaik so I don't think there's a debate here.

>From my understanding, the main discussion revolves around isolation,
ie, whether to change the NUMA core to add nodes on which no allocation
will take place by default or not.

Ben.

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