On Fri, Mar 05, 2021 at 04:19:01AM +0000, Matthew Wilcox (Oracle) wrote:

Cachefiles was relying on wait_page_key and wait_bit_key being the
same layout, which is fragile.  Now that wait_page_key is exposed in
the pagemap.h header, we can remove that fragility.  Also switch it
to use the folio directly instead of the page.

Yikes.  That fix itself is something that should go into mainline ASAP as
it fixes a massive landmine instead of mixing it up with the folio
conversion.