A question about the patch(commit :c777e2a8b654 powerpc/mm: Fix Multi hit ERAT cause by recent THP update)

[zhong jiang <zhongjiang@xxxxxxxxxx>]

Hi  Aneesh

                CPU0                            CPU1
    shrink_page_list()
      add_to_swap()
        split_huge_page_to_list()
          __split_huge_pmd_locked()
            pmdp_huge_clear_flush_notify()
        // pmd_none() == true
                                        exit_mmap()
                                          unmap_vmas()
                                            zap_pmd_range()
                                              // no action on pmd since pmd_none() == true
        pmd_populate()


the mm should be the last user  when CPU1 process is exiting,  CPU0 must be a own mm .
two different process  should not be influenced each other.  in a words , they should not
have race.

I want to know if I missing the point.

Thanks
zhongjiang

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