Re: [PATCH 04/15] mm: remove the pgmap field from struct hmm_vma_walk

[Christoph Hellwig]

On Tue, Aug 13, 2019 at 06:36:33PM -0700, Dan Williams wrote:
> Section alignment constraints somewhat save us here. The only example
> I can think of a PMD not containing a uniform pgmap association for
> each pte is the case when the pgmap overlaps normal dram, i.e. shares
> the same 'struct memory_section' for a given span. Otherwise, distinct
> pgmaps arrange to manage their own exclusive sections (and now
> subsections as of v5.3). Otherwise the implementation could not
> guarantee different mapping lifetimes.
> 
> That said, this seems to want a better mechanism to determine "pfn is
> ZONE_DEVICE".

So I guess this patch is fine for now, and once you provide a better
mechanism we can switch over to it?