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

[David Hildenbrand (Arm)]

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.

IOW something like: