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

Kirill A. Shutemov
2022-04-13T11:38:40Z

On Mon, Apr 11, 2022 at 01:07:29PM +0300, Mike Rapoport wrote:
> 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.

PG_buddy gets clear on remove from the free list, before the chec.

PG_offline and PG_table pages are never on free lists.

--
Kirill A. Shutemov