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

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Message-ID: <DD051CFE-9B2A-4140-9D90-8B3F8C8D80FC@nvidia.com>
Date: Mon, 23 Jun 2025 12:05:04 -0400
From: Zi Yan <ziy@...dia.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
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 Shakeel Butt <shakeel.butt@...ux.dev>
Subject: Re: [PATCH RFC 16/29] mm: rename __PageMovable() to
 page_has_movable_ops()

On 23 Jun 2025, at 11:47, David Hildenbrand wrote:

> 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. */

Sounds good to me.

>
> ... 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.

Right. It becomes clear at Patch 20.

Reviewed-by: Zi Yan <ziy@...dia.com>

--
Best Regards,
Yan, Zi