Merge branch 'anonvma'

* anonvma:
  anonvma: when setting up page->mapping, we need to pick the _oldest_ anonvma
  anon_vma: clone the anon_vma chain in the right order
  vma_adjust: fix the copying of anon_vma chains
  Simplify and comment on anon_vma re-use for anon_vma_prepare()