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.
