Re: [PATCH v1 04/11] mm/memremap: add ZONE_DEVICE support for compound pages

[Aneesh Kumar K.V]

IIUC this series is about devdax namespace with aligh of 1G or 2M where we can
save the vmmemap space by not allocating memory for tail struct pages? 

Dan Williams <dan.j.willi...@intel.com> writes:

> > enum:
>> >
>> > enum devmap_geometry {
>> >     DEVMAP_PTE,
>> >     DEVMAP_PMD,
>> >     DEVMAP_PUD,
>> > }
>> >
>> I suppose a converter between devmap_geometry and page_size would be needed 
>> too? And maybe
>> the whole dax/nvdimm align values change meanwhile (as a followup 
>> improvement)?
>
> I think it is ok for dax/nvdimm to continue to maintain their align
> value because it should be ok to have 4MB align if the device really
> wanted. However, when it goes to map that alignment with
> memremap_pages() it can pick a mode. For example, it's already the
> case that dax->align == 1GB is mapped with DEVMAP_PTE today, so
> they're already separate concepts that can stay separate.

devdax namespace with align of 1G implies we expect to map them with 1G
pte entries? I didn't follow when you say we map them today with
DEVMAP_PTE entries.


-aneesh
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