Re: [RFC PATCH 6/9] iomap: use set/clear_fs_page_private

[Christoph Hellwig]

On Sun, Apr 26, 2020 at 05:26:31PM -0700, Matthew Wilcox wrote:
> On Sun, Apr 26, 2020 at 11:49:22PM +0200, Guoqing Jiang wrote:
> > @@ -59,24 +59,18 @@ iomap_page_create(struct inode *inode, struct page *page)
> >  	 * migrate_page_move_mapping() assumes that pages with private data have
> >  	 * their count elevated by 1.
> >  	 */
> > -	get_page(page);
> > -	set_page_private(page, (unsigned long)iop);
> > -	SetPagePrivate(page);
> > -	return iop;
> > +	return (struct iomap_page *)set_fs_page_private(page, iop);
> >  }
> 
> This cast is unnecessary.  void * will be automatically cast to the
> appropriate pointer type.

I also find the pattern eather strange.  A:

	attach_page_private(page, iop);
	return iop;

explains the intent much better.