uprobe: collapse THP pmd after removing all uprobes

uprobe: collapse THP pmd after removing all uprobes

After all uprobes are removed from the huge page (with PTE pgtable), it is
possible to collapse the pmd and benefit from THP again.  This patch does
the collapse by calling collapse_pte_mapped_thp().

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Song Liu <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Reported-by: kbuild test robot <[email protected]>
Reviewed-by: Oleg Nesterov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>