Re: [RFC PATCH V2 1/9] include/linux/pagemap.h: introduce attach/clear_page_private

[Andreas GrÃnbacher]

Hi,

Am Do., 30. Apr. 2020 um 23:56 Uhr schrieb Guoqing Jiang
<guoqing.jiang@xxxxxxxxxxxxxxx>:
> The logic in attach_page_buffers and  __clear_page_buffers are quite
> paired, but
>
> 1. they are located in different files.
>
> 2. attach_page_buffers is implemented in buffer_head.h, so it could be
>    used by other files. But __clear_page_buffers is static function in
>    buffer.c and other potential users can't call the function, md-bitmap
>    even copied the function.
>
> So, introduce the new attach/clear_page_private to replace them. With
> the new pair of function, we will remove the usage of attach_page_buffers
> and  __clear_page_buffers in next patches. Thanks for the new names from
> Christoph Hellwig.
>
> Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
> Cc: William Kucharski <william.kucharski@xxxxxxxxxx>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
> Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
> Cc: Yafang Shao <laoar.shao@xxxxxxxxx>
> Cc: Song Liu <song@xxxxxxxxxx>
> Cc: linux-raid@xxxxxxxxxxxxxxx
> Cc: Chris Mason <clm@xxxxxx>
> Cc: Josef Bacik <josef@xxxxxxxxxxxxxx>
> Cc: David Sterba <dsterba@xxxxxxxx>
> Cc: linux-btrfs@xxxxxxxxxxxxxxx
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> Cc: Chao Yu <chao@xxxxxxxxxx>
> Cc: linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Cc: linux-xfs@xxxxxxxxxxxxxxx
> Cc: Anton Altaparmakov <anton@xxxxxxxxxx>
> Cc: linux-ntfs-dev@xxxxxxxxxxxxxxxxxxxxx
> Cc: Mike Marshall <hubcap@xxxxxxxxxxxx>
> Cc: Martin Brandenburg <martin@xxxxxxxxxxxx>
> Cc: devel@xxxxxxxxxxxxxxxxxx
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Cc: Roman Gushchin <guro@xxxxxx>
> Cc: Andreas Dilger <adilger@xxxxxxxxx>
> Signed-off-by: Guoqing Jiang <guoqing.jiang@xxxxxxxxxxxxxxx>
> ---
> RFC -> RFC V2:  Address the comments from Christoph Hellwig
> 1. change function names to attach/clear_page_private and add comments.
> 2. change the return type of attach_page_private.
>
>  include/linux/pagemap.h | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index a8f7bd8ea1c6..2e515f210b18 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -205,6 +205,41 @@ static inline int page_cache_add_speculative(struct page *page, int count)
>         return __page_cache_add_speculative(page, count);
>  }
>
> +/**
> + * attach_page_private - attach data to page's private field and set PG_private.
> + * @page: page to be attached and set flag.
> + * @data: data to attach to page's private field.
> + *
> + * Need to take reference as mm.h said "Setting PG_private should also increment
> + * the refcount".
> + */
> +static inline void attach_page_private(struct page *page, void *data)
> +{
> +       get_page(page);
> +       set_page_private(page, (unsigned long)data);
> +       SetPagePrivate(page);
> +}
> +
> +/**
> + * clear_page_private - clear page's private field and PG_private.
> + * @page: page to be cleared.
> + *
> + * The counterpart function of attach_page_private.
> + * Return: private data of page or NULL if page doesn't have private data.
> + */
> +static inline void *clear_page_private(struct page *page)
> +{
> +       void *data = (void *)page_private(page);
> +
> +       if (!PagePrivate(page))
> +               return NULL;
> +       ClearPagePrivate(page);
> +       set_page_private(page, 0);
> +       put_page(page);
> +
> +       return data;
> +}
> +

I like this in general, but the name clear_page_private suggests that
this might be the inverse operation of set_page_private, which it is
not. So maybe this can be renamed to detach_page_private to more
clearly indicate that it pairs with attach_page_private?

>  #ifdef CONFIG_NUMA
>  extern struct page *__page_cache_alloc(gfp_t gfp);
>  #else
> --
> 2.17.1
>

Thanks,
Andreas