Re: [PATCH v4 3/6] mm: rmap: introduce pfn_mkclean_range() to cleans PTEs

[Dan Williams]

On Wed, Mar 9, 2022 at 4:26 PM Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>
> On Wed, Mar 2, 2022 at 12:29 AM Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:
> >
> > The page_mkclean_one() is supposed to be used with the pfn that has a
> > associated struct page, but not all the pfns (e.g. DAX) have a struct
> > page. Introduce a new function pfn_mkclean_range() to cleans the PTEs
> > (including PMDs) mapped with range of pfns which has no struct page
> > associated with them. This helper will be used by DAX device in the
> > next patch to make pfns clean.
>
> This seems unfortunate given the desire to kill off
> CONFIG_FS_DAX_LIMITED which is the only way to get DAX without 'struct
> page'.
>
> I would special case these helpers behind CONFIG_FS_DAX_LIMITED such
> that they can be deleted when that support is finally removed.

...unless this support is to be used for other PFN_MAP scenarios where
a 'struct page' is not available? If so then the "(e.g. DAX)" should
be clarified to those other cases.