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

[Guoqing Jiang]

On 5/1/20 12:10 AM, Andreas GrÃnbacher wrote:
> 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?

Yes, the new name is better, thank you!

Cheers,
Guoqing