Avoid down_write of the mmap_sem in madvise when we can help it.
Acked-by: NHugh Dickins <hugh@veritas.com>
Signed-off-by: NNick Piggin <npiggin@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>