# Re: \[PATCH v1 04/11\] mm/memremap: add ZONE\_DEVICE support for compound pages

- From: Aneesh Kumar K.V \<hidden\>
- Date: 2021-05-06 08:06:04 
- List: linux-mm
- Page: https://ratatoskr.run/linux-mm/2021/05/6507982
- Thread: https://ratatoskr.run/linux-mm/2021/03/6507171/t.md

```text


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 [ref] 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

```