On Mon, Aug 2, 2021 at 3:41 AM Joao Martins [off-list ref] wrote:

On 7/28/21 12:23 AM, Dan Williams wrote:

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On Thu, Jul 22, 2021 at 3:54 AM Joao Martins [off-list ref] wrote:
[..]

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The folio work really touches the page
cache for now, and this seems mostly to touch the devmap paths.

/me nods -- it really is about devmap infra for usage in device-dax for persistent memory.

Perhaps I should do s/pagemaps/devmap/ throughout the series to avoid confusion.

I also like "devmap" as a more accurate name. It matches the PFN_DEV
and PFN_MAP flags that decorate DAX capable pfn_t instances. It also
happens to match a recommendation I gave to Ira for his support for
supervisor protection keys with devmap pfns.

/me nods

Additionally, I think I'll be reordering the patches for more clear/easier
bisection i.e. first introducing compound pages for devmap, fixing associated
issues wrt to the slow pinning and then introduce vmemmap deduplication for
devmap.

It should look like below after the reordering from first patch to last.
Let me know if you disagree.

memory-failure: fetch compound_head after pgmap_pfn_valid()
mm/page_alloc: split prep_compound_page into head and tail subparts
mm/page_alloc: refactor memmap_init_zone_device() page init
mm/memremap: add ZONE_DEVICE support for compound pages
device-dax: use ALIGN() for determining pgoff
device-dax: compound devmap support
mm/gup: grab head page refcount once for group of subpages
mm/sparse-vmemmap: add a pgmap argument to section activation
mm/sparse-vmemmap: refactor core of vmemmap_populate_basepages() to helper
mm/hugetlb_vmemmap: move comment block to Documentation/vm
mm/sparse-vmemmap: populate compound devmaps
mm/page_alloc: reuse tail struct pages for compound devmaps
mm/sparse-vmemmap: improve memory savings for compound pud geometry

LGTM.