Strange condition in invalidate_mapping_pages()

[Jan Kara <jack@suse.cz>]

Hi Kirill,

in commit fc127da085c26 "truncate: handle file thp" you've added the
following to invalidate_mapping_pages():

          /* Middle of THP: skip */
          if (PageTransTail(page)) {
                  unlock_page(page);
                  continue;
          } else if (PageTransHuge(page)) {
                  index += HPAGE_PMD_NR - 1;
                  i += HPAGE_PMD_NR - 1;
                  /* 'end' is in the middle of THP */
                  if (index ==  round_down(end, HPAGE_PMD_NR))
                          continue;
          }

Now how can ever condition "if (index ==  round_down(end,
HPAGE_PMD_NR))" be true? We have just added HPAGE_PMD_NR - 1 to 'index'
so it will not be a multiple of HPAGE_PMD_NR. Presumably you wanted to
check whether the current THP is the one containing 'end' here which would
be something like 'round_down(index, HPAGE_PMD_NR) == round_down(end,
HPAGE_PMD_NR)' but then I still miss why you'd like to avoid invalidating
the partial THP at the end of file... Can you please enlighten me? Thanks!

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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