Re: [RFC PATCH 3/9] btrfs: use set/clear_fs_page_private

[Christoph Hellwig]

On Mon, Apr 27, 2020 at 08:20:54AM +1000, Dave Chinner wrote:
> >  void set_page_extent_mapped(struct page *page)
> >  {
> > -	if (!PagePrivate(page)) {
> > -		SetPagePrivate(page);
> > -		get_page(page);
> > -		set_page_private(page, EXTENT_PAGE_PRIVATE);
> > -	}
> > +	if (!PagePrivate(page))
> > +		set_fs_page_private(page, (void *)EXTENT_PAGE_PRIVATE);
> 
> Change the definition of EXTENT_PAGE_PRIVATE so the cast is not
> needed? Nothing ever reads EXTENT_PAGE_PRIVATE; it's only there to
> set the private flag for other code to check and release the extent
> mapping reference to the page...

IIRC there as a patch on the btrfs list to remove EXTENT_PAGE_PRIVATE,
it might be better to not bother changing it.  Maybe the btrfs
maintainers remember this better.