[PATCH v4 4/5] mm/filemap: add write_begin_get_folio() helper function

[hanqi]

在 2025/7/7 15:00, 陈涛涛 Taotao Chen 写道:
> From: Taotao Chen <chentaotao at didiglobal.com>
>
> Add write_begin_get_folio() to simplify the common folio lookup logic
> used by filesystem ->write_begin() implementations.
>
> This helper wraps __filemap_get_folio() with common flags such as
> FGP_WRITEBEGIN, conditional FGP_DONTCACHE, and set folio order based
> on the write length.
>
> Part of a series refactoring address_space_operations write_begin and
> write_end callbacks to use struct kiocb for passing write context and
> flags.
>
> Signed-off-by: Taotao Chen <chentaotao at didiglobal.com>
> ---
>   include/linux/pagemap.h |  3 +++
>   mm/filemap.c            | 30 ++++++++++++++++++++++++++++++
>   2 files changed, 33 insertions(+)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index e63fbfbd5b0f..cbf8539ba11b 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -749,6 +749,9 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
>   		fgf_t fgp_flags, gfp_t gfp);
>   struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
>   		fgf_t fgp_flags, gfp_t gfp);
> +struct folio *write_begin_get_folio(const struct kiocb *iocb,
> +				    struct address_space *mapping,
> +				    pgoff_t index, size_t len);
>   
>   /**
>    * filemap_get_folio - Find and get a folio.
> diff --git a/mm/filemap.c b/mm/filemap.c
> index ba089d75fc86..9520f65c287a 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2026,6 +2026,36 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
>   }
>   EXPORT_SYMBOL(__filemap_get_folio);
>   
> +
> +/**
> + * write_begin_get_folio - Get folio for write_begin with flags
> + * @iocb: kiocb passed from write_begin (may be NULL)
> + * @mapping: the address space to search in
> + * @index: page cache index
> + * @len: length of data being written
> + *
> + * This is a helper for filesystem write_begin() implementations.
> + * It wraps __filemap_get_folio(), setting appropriate flags in
> + * the write begin context.
> + *
> + * Returns a folio or an ERR_PTR.
> + */

hi, tao
I think it might be worth considering adding an fgf_t parameter to the
write_begin_get_folio() helper, since in some filesystems the fgp_flags
passed to __filemap_get_folio() in write_begin are not limited to just
FGP_WRITEBEGIN. Something like:
struct folio *write_begin_get_folio(const struct kiocb *iocb,
				    struct address_space *mapping,
				    pgoff_t index, size_t len,
                                     fgf_t fgp_flags)

> +struct folio *write_begin_get_folio(const struct kiocb *iocb,
> +				    struct address_space *mapping,
> +				    pgoff_t index, size_t len)
> +{
> +	fgf_t fgp_flags = FGP_WRITEBEGIN;
> +
> +	fgp_flags |= fgf_set_order(len);
> +
> +	if (iocb && iocb->ki_flags & IOCB_DONTCACHE)
> +		fgp_flags |= FGP_DONTCACHE;
> +
> +	return __filemap_get_folio(mapping, index, fgp_flags,
> +				   mapping_gfp_mask(mapping));
> +}
> +EXPORT_SYMBOL(write_begin_get_folio);
> +
>   static inline struct folio *find_get_entry(struct xa_state *xas, pgoff_t max,
>   		xa_mark_t mark)
>   {