I got lots of NULL pointer dereference Oops when compiling kernel on ceph.
The bug is because the kernel page migration routine replaces some pages
in the page cache with new pages, these new pages' private can be non-zero.
Signed-off-by: NZheng Yan <zheng.z.yan@intel.com>
Signed-off-by: NSage Weil <sage@inktank.com>
(cherry picked from commit 28c0254e)