Re: [PATCH v11 04/25] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages

Dan Williams
2019-12-19T06:52:47Z

On Wed, Dec 18, 2019 at 9:51 PM John Hubbard <jhubbard@nvidia.com> wrote:
>
> On 12/18/19 9:27 PM, Dan Williams wrote:
> ...
> >> @@ -461,5 +449,5 @@ void __put_devmap_managed_page(struct page *page)
> >> page->mapping = NULL;
> >> page->pgmap->ops->page_free(page);
> >> }
> >> -EXPORT_SYMBOL(__put_devmap_managed_page);
> >> +EXPORT_SYMBOL(free_devmap_managed_page);
> >
> > This patch does not have a module consumer for
> > free_devmap_managed_page(), so the export should move to the patch
> > that needs the new export.
>
> Hi Dan,
>
> OK, I know that's a policy--although it seems quite pointless here given
> that this is definitely going to need an EXPORT.
>
> At the moment, the series doesn't use it in any module at all, so I'll just
> delete the EXPORT for now.
>
> >
> > Also the only reason that put_devmap_managed_page() is EXPORT_SYMBOL
> > instead of EXPORT_SYMBOL_GPL is that there was no practical way to
> > hide the devmap details from evey module in the kernel that did
> > put_page(). I would expect free_devmap_managed_page() to
> > EXPORT_SYMBOL_GPL if it is not inlined into an existing exported
> > static inline api.
> >
>
> Sure, I'll change it to EXPORT_SYMBOL_GPL when the time comes. We do have
> to be careful that we don't shut out normal put_page() types of callers,
> but...glancing through the current callers, that doesn't look to be a problem.
> Good. So it should be OK to do EXPORT_SYMBOL_GPL here.
>
> Are you *sure* you don't want to just pre-emptively EXPORT now, and save
> looking at it again?

I'm positive. There is enough history for "trust me the consumer is
coming" turning out not to be true to justify the hassle in my mind. I
do trust you, but things happen.