Pull device mapper updates from Mike Snitzer:
- Adjust various DM structure members to improve alignment relative to
4.18 block's mempool_t and bioset changes.
- Add DM writecache target that offers writeback caching to persistent
memory or SSD.
- Small DM core error message change to give context for why a DM table
type transition wasn't allowed.
* tag 'for-4.18/dm-changes-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm:
dm: add writecache target
dm: adjust structure members to improve alignment
dm: report which conflicting type caused error during table_load()