linux-kernel - Re: [PATCH RFC 16/29] mm: rename __PageMovable() to page_has_movable

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Message-ID: <d6208fab-9ab5-485e-9cc3-94256fef2e1b@redhat.com>
Date: Mon, 23 Jun 2025 17:47:26 +0200
From: David Hildenbrand <david@...hat.com>
To: Zi Yan <ziy@...dia.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
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Subject: Re: [PATCH RFC 16/29] mm: rename __PageMovable() to
 page_has_movable_ops()

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@...hat.com>
>> ---
>>   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