Re: [PATCH v1 18/29] mm: remove __folio_test_movable()

[David Hildenbrand]

> > ---
> >   include/linux/page-flags.h |  6 ------
> >   mm/migrate.c               | 43 ++++++++++++--------------------------
> >   mm/vmscan.c                |  6 ++++--
> >   3 files changed, 17 insertions(+), 38 deletions(-)
> >
> > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> > index c67163b73c5ec..4c27ebb689e3c 100644
> > --- a/include/linux/page-flags.h
> > +++ b/include/linux/page-flags.h
> > @@ -744,12 +744,6 @@ static __always_inline bool PageAnon(const struct page *page)
> >   	return folio_test_anon(page_folio(page));
> >   }
> >
> > -static __always_inline bool __folio_test_movable(const struct folio *folio)
> > -{
> > -	return ((unsigned long)folio->mapping & PAGE_MAPPING_FLAGS) ==
> > -			PAGE_MAPPING_MOVABLE;
> > -}
> > -
>
> Woah, wait, does this mean we can remove PAGE_MAPPING_MOVABLE??

Jup :)

> Nice!
>
> >   static __always_inline bool page_has_movable_ops(const struct page *page)
> >   {
> >   	return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index 587af35b7390d..15d3c1031530c 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -219,12 +219,7 @@ void putback_movable_pages(struct list_head *l)
> >   			continue;
> >   		}
> >   		list_del(&folio->lru);
> > -		/*
> > -		 * We isolated non-lru movable folio so here we can use
> > -		 * __folio_test_movable because LRU folio's mapping cannot
> > -		 * have PAGE_MAPPING_MOVABLE.
> > -		 */
>
> So hate these references to 'LRU' as in meaning 'pages that could be on the
> LRU'.

Yeah, it's a historical thing.

But for anything we isolated, it had to be an LRU folio (PageLRU) 
because that's how we were even able to isolate it ... from the LRU.

[...]

> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 098bcc821fc74..103dfc729a823 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -1658,9 +1658,11 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
> >   	unsigned int noreclaim_flag;
> >
> >   	list_for_each_entry_safe(folio, next, folio_list, lru) {
> > +		/* TODO: these pages should not even appear in this list. */
> > +		if (page_has_movable_ops(&folio->page))
>
> VM_WARN_ON_ONCE()?

Well, no, it can currently still happen. But really, movable_ops pages 
are not folios that could ever be reclaimed that way.

So the TODO highlights that movable_ops pages should never even be put 
in a list (page->lru will go away).

--
Cheers,

David / dhildenb