Re: [GIT PULL] Memory folios for v5.15

[Dan Williams]

On Fri, Aug 27, 2021 at 11:47 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Fri, Aug 27, 2021 at 10:07:16AM -0400, Johannes Weiner wrote:
> > 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.