On Fri, Aug 27, 2021 at 11:47 AM Matthew Wilcox [off-list ref] wrote:

On Fri, Aug 27, 2021 at 10:07:16AM -0400, Johannes Weiner wrote:

quoted

We have the same thoughts in MM and growing memory sizes. The DAX
stuff said from the start it won't be built on linear struct page
mappings anymore because we expect the memory modules to be too big to
manage them with such fine-grained granularity.

Well, I did.  Then I left Intel, and Dan took over.  Now we have a struct
page for each 4kB of PMEM.  I'm not particularly happy about this change
of direction.

Page-less DAX left more problems than it solved. Meanwhile,
ZONE_DEVICE has spawned other useful things like peer-to-peer DMA.

I am more encouraged by efforts to make the 'struct page' overhead
disappear, first from Muchun Song for hugetlbfs and recently Joao
Martins for device-dax.  If anything, I think 'struct page' for PMEM /
DAX *strengthens* the case for folios / better mechanisms to reduce
the overhead of tracking 4K pages.