Re: [PATCH v3 06/14] f2fs: stop using PG_private

[Chao Yu]

On 9/10/26 15:34, David Hildenbrand (Arm) wrote:
> On 9/10/26 04:41, Chao Yu wrote:
>> On 9/8/26 23:47, David Hildenbrand (Arm) wrote:
>>> On 9/8/26 04:56, Zi Yan wrote:
>>>> f2fs sets its PAGE_PRIVATE_* flags in page->private and checking
>>>> page->private != NULL is equivalent to checking PG_private. Change
>>>> PagePrivate() to page_private(). Meanwhile, in set_page_private_##name(),
>>>> page->private is first set to 0/NULL before an PAGE_PRIVATE_* flag is set,
>>>> but it can cause confusion when PG_private is removed and
>>>> page->private != NULL is used instead. Change it to initialize
>>>> page->private to PAGE_PRIVATE_NOT_POINTER instead and retain the original
>>>> semantics.
>>>>
>>>> It prepares for a future commit that removes PG_private.
>>>>
>>>> No functional change intended.
>>>>
>>>> Assisted-by: Claude:claude-opus-4-8
>>>> Assisted-by: Codex:gpt-5
>>>> To: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
>>>> To: Chao Yu <chao@xxxxxxxxxx>
>>>> Cc: linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
>>>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>>>> Acked-by: Usama Arif <usama.arif@xxxxxxxxx>
>>>> Acked-by: Chao Yu <chao@xxxxxxxxxx>
>>>> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
>>>> ---
>>>>  fs/f2fs/f2fs.h | 8 ++++----
>>>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>> index 9940a6cecf1a2..2f7ab5888b078 100644
>>>> --- a/fs/f2fs/f2fs.h
>>>> +++ b/fs/f2fs/f2fs.h
>>>> @@ -2691,7 +2691,7 @@ static inline bool folio_test_f2fs_##name(const struct folio *folio)	\
>>>>  }									\
>>>>  static inline bool page_private_##name(struct page *page) \
>>>>  { \
>>>> -	return PagePrivate(page) && \
>>>> +	return page_private(page) && \
>>>>  		test_bit(PAGE_PRIVATE_NOT_POINTER, &page_private(page)) && \
>>>>  		test_bit(PAGE_PRIVATE_##flagname, &page_private(page)); \
>>>>  }
>>>> @@ -2710,9 +2710,9 @@ static inline void folio_set_f2fs_##name(struct folio *folio)		\
>>>>  }									\
>>>>  static inline void set_page_private_##name(struct page *page) \
>>>>  { \
>>>> -	if (!PagePrivate(page)) \
>>>> -		attach_page_private(page, (void *)0); \
>>>> -	set_bit(PAGE_PRIVATE_NOT_POINTER, &page_private(page)); \
>>>> +	if (!page_private(page)) \
>>>> +		attach_page_private(page, \
>>>> +				(void *)BIT(PAGE_PRIVATE_NOT_POINTER)); \
>>>>  	set_bit(PAGE_PRIVATE_##flagname, &page_private(page)); \
>>>>  }
>>>
>>> Very weird interface. Why do we even need the page-based interface still?
>>>
>>> $ git grep -E "(set|clear)_page_private"
>>> compress.c:             clear_page_private_gcing(cc->rpages[i]);
>>> compress.c:                     set_page_private_gcing(cc->rpages[i]);
>>> compress.c:             clear_page_private_gcing(cic->rpages[i]);
>>> f2fs.h:static inline void set_page_private_##name(struct page *page) \
>>> f2fs.h:static inline void clear_page_private_##name(struct page *page) \
>>>
>>> Seeing code like:
>>>
>>> clear_page_private_gcing(cc->rpages[i]);
>>> if (folio_test_writeback(page_folio(cc->rpages[i])))
>>> 	end_page_writeback(cc->rpages[i]);
>>>
>>> Makes me wonder whether we can just use the folio helper instead?
>>>
>>> In f2fs_iget(), we enable large folios only when !f2fs_compressed_file(inode).
>>>
>>> So naive me would assume that we can just get rid of the
>>> set_page_private_/clear_page_private_ stuff entirely.
>>
>> David,
>>
>> Thanks for the patch, at a glance, it seems fine, can you please send
>> a formal patch? then we can apply to dev-test for test.
> 
> I'm hoping Zi will drag that along as part of this patch set. Is this fine or do

Oh, I see.

> you want it sent as a complete standalone patch (will make merging Zi's series
> slightly more complicated :) ).

I think sending as a separated patch based on Zi Yan's patch is fine, since the
purpose of this patch is a little different from Zi's one.

Note that: ("f2fs: stop using PG_private") has been merged in
https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git/log/?h=dev-test,

Thanks,