Re: [PATCH v2 1/3] mm: document zone device struct page field usage

[Ralph Campbell]

On 7/22/19 4:08 AM, Matthew Wilcox wrote:
> On Sun, Jul 21, 2019 at 10:13:45PM -0700, Ira Weiny wrote:
> > On Sun, Jul 21, 2019 at 09:02:04AM -0700, Matthew Wilcox wrote:
> > > On Fri, Jul 19, 2019 at 12:29:53PM -0700, Ralph Campbell wrote:
> > > > Struct page for ZONE_DEVICE private pages uses the page->mapping and
> > > > and page->index fields while the source anonymous pages are migrated to
> > > > device private memory. This is so rmap_walk() can find the page when
> > > > migrating the ZONE_DEVICE private page back to system memory.
> > > > ZONE_DEVICE pmem backed fsdax pages also use the page->mapping and
> > > > page->index fields when files are mapped into a process address space.
> > > >
> > > > Restructure struct page and add comments to make this more clear.
> > >
> > > NAK.  I just got rid of this kind of foolishness from struct page,
> > > and you're making it harder to understand, not easier.  The comments
> > > could be improved, but don't lay it out like this again.
> >
> > Was V1 of Ralphs patch ok?  It seemed ok to me.
>
> Yes, v1 was fine.  This seems like a regression.

This is about what people find "easiest to understand" and so
I'm not surprised that opinions differ.
What if I post a v3 based on v1 but remove the _zd_pad_* variables
that Christoph found misleading and add some more comments
about how the different ZONE_DEVICE types use the 3 remaining
words (basically the comment from v2)?