Pull device mapper updates from Mike Snitzer:

 - DM core cleanups:

     * blk-mq request-based DM no longer uses any mempools now that
       partial completions are no longer handled as part of cloned
       requests

 - DM raid cleanups and support for MD raid0

 - DM cache core advances and a new stochastic-multi-queue (smq) cache
   replacement policy

     * smq is the new default dm-cache policy

 - DM thinp cleanups and much more efficient large discard support

 - DM statistics support for request-based DM and nanosecond resolution
   timestamps

 - Fixes to DM stripe, DM log-writes, DM raid1 and DM crypt

* tag 'dm-4.2-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm: (39 commits)
  dm stats: add support for request-based DM devices
  dm stats: collect and report histogram of IO latencies
  dm stats: support precise timestamps
  dm stats: fix divide by zero if 'number_of_areas' arg is zero
  dm cache: switch the "default" cache replacement policy from mq to smq
  dm space map metadata: fix occasional leak of a metadata block on resize
  dm thin metadata: fix a race when entering fail mode
  dm thin: fail messages with EOPNOTSUPP when pool cannot handle messages
  dm thin: range discard support
  dm thin metadata: add dm_thin_remove_range()
  dm thin metadata: add dm_thin_find_mapped_range()
  dm btree: add dm_btree_remove_leaves()
  dm stats: Use kvfree() in dm_kvfree()
  dm cache: age and write back cache entries even without active IO
  dm cache: prefix all DMERR and DMINFO messages with cache device name
  dm cache: add fail io mode and needs_check flag
  dm cache: wake the worker thread every time we free a migration object
  dm cache: add stochastic-multi-queue (smq) policy
  dm cache: boost promotion of blocks that will be overwritten
  dm cache: defer whole cells
  ...