Re: [PATCHv4 1/8] mm: Add support for unaccepted memory

Mike Rapoport
2022-04-11T10:07:40Z

On Sun, Apr 10, 2022 at 11:38:08PM -0700, Dave Hansen wrote:
> On 4/9/22 08:54, Kirill A. Shutemov wrote:
> > On Fri, Apr 08, 2022 at 11:55:43AM -0700, Dave Hansen wrote:
>
> >>> if (fpi_flags & FPI_TO_TAIL)
> >>> to_tail = true;
> >>> else if (is_shuffle_order(order))
> >>> @@ -1149,7 +1192,8 @@ static inline void __free_one_page(struct page *page,
> >>> static inline bool page_expected_state(struct page *page,
> >>> unsigned long check_flags)
> >>> {
> >>> - if (unlikely(atomic_read(&page->_mapcount) != -1))
> >>> + if (unlikely(atomic_read(&page->_mapcount) != -1) &&
> >>> + !PageUnaccepted(page))
> >>> return false;
> >>
> >> That probably deserves a comment, and maybe its own if() statement.
> >
> > Own if does not work. PageUnaccepted() is encoded in _mapcount.
> >
> > What about this:
> >
> > /*
> > * page->_mapcount is expected to be -1.
> > *
> > * There is an exception for PageUnaccepted(). The page type can be set
> > * for pages on free list. Page types are encoded in _mapcount.
> > *
> > * PageUnaccepted() will get cleared in post_alloc_hook().
> > */
> > if (unlikely((atomic_read(&page->_mapcount) | PG_unaccepted) != -1))

Maybe I'm missing something, but isn't this true for any PageType?

> > return false;
> >
> > ?
>
> That's better. But, aren't the PG_* names usually reserved for real
> page->flags bits? That naming might be part of my confusion.

We use them for PageType as well like PG_buddy, PG_offline, PG_Table.

--
Sincerely yours,
Mike.