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

David Hildenbrand
2025-07-01T12:36:24Z

>> ---
>> 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