On Thu, Apr 09, 2020 at 07:15:50AM -0700, Matthew Wilcox wrote:
> On Thu, Apr 09, 2020 at 05:09:14PM +0300, Kirill A. Shutemov wrote:
> > On Wed, Apr 08, 2020 at 08:01:44AM -0700, Matthew Wilcox wrote:
> > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> > > index 4aba6c0c2ba8..a8c3fa076f43 100644
> > > --- a/include/linux/mm_types.h
> > > +++ b/include/linux/mm_types.h
> > > @@ -221,15 +221,8 @@ struct page {
> > > #endif
> > > } _struct_page_alignment;
> > >
> > > -static inline atomic_t *compound_mapcount_ptr(struct page *page)
> > > -{
> > > - return &page[1].compound_mapcount;
> > > -}
> > > -
> > > -static inline atomic_t *compound_pincount_ptr(struct page *page)
> > > -{
> > > - return &page[2].hpage_pinned_refcount;
> > > -}
> > > +#define compound_mapcount_ptr(page) (&(page)[1].compound_mapcount)
> > > +#define compound_pincount_ptr(page) (&(page)[2].hpage_pinned_refcount)
> >
> > Looks like this conversion is not covered by the reason given in the
> > commit message. Hm?
>
> They were supposed to be covered by "That means some inline functions
> have to become macros so they can return a struct page which is the same
> const-ness as their argument."
>
> They're not quite covered since they need to return an atomic_t that
> is the same constness as their argument.
Ah, right.
> > > +#define compound_head(page) ({ \
> > > + __typeof__(page) _page = page; \
> > > + unsigned long head = READ_ONCE(_page->compound_head); \
> > > + if (unlikely(head & 1)) \
> > > + _page = (void *)(head - 1); \
> > > + _page; \
> > > +})
> >
> > Ugh..
> >
> > Other option would be to make compound_head() take 'const struct page *'
> > and return 'void *'. It arguably would provide better type safety, no?
>
> We have a few places that do things like
>
> mm/filemap.c: if (unlikely(compound_head(page)->mapping != mapping)) {
Good point.
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
--
Kirill A. Shutemov
