Merge branch 'md-next' of https://git.kernel.org/pub/scm/linux/kernel/git/song/md...

Pull MD updates from Song.

* 'md-next' of https://git.kernel.org/pub/scm/linux/kernel/git/song/md:
  md/raid10: improve discard request for far layout
  md/raid10: improve raid10 discard request
  md/raid10: pull codes that wait for blocked dev into one function
  md/raid10: extend r10bio devs to raid disks
  md: add md_submit_discard_bio() for submitting discard bio
  md: Simplify code with existing definition RESYNC_SECTORS in raid10.c
  md/raid5: reallocate page array after setting new stripe_size
  md/raid5: resize stripe_head when reshape array
  md/raid5: let multiple devices of stripe_head share page
  md/raid6: let async recovery function support different page offset
  md/raid6: let syndrome computor support different page offset
  md/raid5: convert to new xor compution interface
  md/raid5: add new xor function to support different page offset
  md/raid5: make async_copy_data() to support different page offset
  md/raid5: add a new member of offset into r5dev
  md: only calculate blocksize once and use i_blocksize()