mm/filemap: fix page cache removal for arbitrary sized THPs

Patch series "Remove assumptions of THP size".

There are a number of places in the VM which assume that a THP is a PMD in
size.  That's true today, and remains true after this patch series, but
this is a prerequisite for switching to arbitrary-sized THPs.
thp_nr_pages() still returns either HPAGE_PMD_NR or 1, but will be changed
later.

This patch (of 11):

page_cache_free_page() assumes THPs are PMD_SIZE; fix that assumption.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Huang Ying <ying.huang@intel.com>
Link: https://lkml.kernel.org/r/20200908195539.25896-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20200908195539.25896-2-willy@infradead.org


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>