Re: [PATCH 1/6] mm/page_io: use a folio in __end_swap_bio_read()

[Christoph Hellwig]

On Tue, Jul 18, 2023 at 05:16:15PM +0100, Matthew Wilcox wrote:
> How does _this_ folio end up in btrfs's write_dev_supers()?  This is a
> swap read.  The only folios which are swapped are anonymous and tmpfs.
> btrfs takes care of doing its own I/O.  wait_dev_supers() is looking
> for the error set in btrfs_end_super_write() which is the completion
> routine for write_dev_supers().  The pages involved there are attached
> to a btrfs address_space, not shmem or anon.

It actually operates on the block_device inode.  That does not matter
for this series, but complicates things in other ways.