thp: increase split_huge_page() success rate

thp: increase split_huge_page() success rate

During freeze_page(), we remove the page from rmap.  It munlocks the
page if it was mlocked.  clear_page_mlock() uses thelru cache, which
temporary pins the page.

Let's drain the lru cache before checking page's count vs.  mapcount.
The change makes mlocked page split on first attempt, if it was not
pinned by somebody else.

Signed-off-by: Kirill A. Shutemov <[email protected]>
Cc: Sasha Levin <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>