Re: [PATCH RFC 16/29] mm: rename __PageMovable() to page_has_movable_ops()

[David Hildenbrand]

On 20.06.25 22:37, Zi Yan wrote:
> On 18 Jun 2025, at 13:39, David Hildenbrand wrote:
>
> > Let's make it clearer that we are talking about movable_ops pages.
> >
> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> > ---
> >   include/linux/migrate.h    |  2 +-
> >   include/linux/page-flags.h |  2 +-
> >   mm/compaction.c            |  7 ++-----
> >   mm/memory-failure.c        |  4 ++--
> >   mm/memory_hotplug.c        |  8 +++-----
> >   mm/migrate.c               |  8 ++++----
> >   mm/page_alloc.c            |  2 +-
> >   mm/page_isolation.c        | 10 +++++-----
> >   8 files changed, 19 insertions(+), 24 deletions(-)
> >
> > diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> > index 204e89eac998f..c575778456f97 100644
> > --- a/include/linux/migrate.h
> > +++ b/include/linux/migrate.h
> > @@ -115,7 +115,7 @@ static inline void __SetPageMovable(struct page *page,
> >   static inline
> >   const struct movable_operations *page_movable_ops(struct page *page)
> >   {
> > -	VM_BUG_ON(!__PageMovable(page));
> > +	VM_BUG_ON(!page_has_movable_ops(page));
> >
> >   	return (const struct movable_operations *)
> >   		((unsigned long)page->mapping - PAGE_MAPPING_MOVABLE);
> > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> > index 4fe5ee67535b2..c67163b73c5ec 100644
> > --- a/include/linux/page-flags.h
> > +++ b/include/linux/page-flags.h
> > @@ -750,7 +750,7 @@ static __always_inline bool __folio_test_movable(const struct folio *folio)
> >   			PAGE_MAPPING_MOVABLE;
> >   }
> >
> > -static __always_inline bool __PageMovable(const struct page *page)
> > +static __always_inline bool page_has_movable_ops(const struct page *page)
> >   {
> >   	return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
> >   				PAGE_MAPPING_MOVABLE;
> > diff --git a/mm/compaction.c b/mm/compaction.c
> > index 5c37373017014..f8b7c09e2e48c 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -1056,11 +1056,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> >   		 * Skip any other type of page
> >   		 */
> >   		if (!PageLRU(page)) {
> > -			/*
> > -			 * __PageMovable can return false positive so we need
> > -			 * to verify it under page_lock.
> > -			 */
> > -			if (unlikely(__PageMovable(page)) &&
> > +			/* Isolation will grab the page lock. */
>
> I feel that the removed comment should stay, since the current comment
> makes no sense when I read it alone.

Well, talking about the page lock is moot either way. The thing is, 
anything can change while we don't hold a page reference. So should we 
change the comment to

/* isolation code will deal with any races. */

... or drop it completely?

> In addition, why is __PageMovable() is renamed to page_has_movable_ops() but
> __SetPageMovable() stays the same? page_has_movable_ops() and __SetPageMovable()
> are functions for checking and setting PAGE_MAPPING_MOVABLE. The naming just
> does not look symmetric.

See follow-up commits where __SetPageMovable() is cleaned up.

--
Cheers,

David / dhildenb