Otherwise we are doing redundant work. Especially since the 'unbind'
and 'unpopulate' have been merged and nouveau driver ends up calling
it quite excessivly. On a GeForce 8600 GT with Gnome Shell (GNOME 3)
we end up spending about 54% CPU time in __change_page_attr_set_clr
checking the page flags.

The callgraph (annotated) looks as so before this patch:

    53.29%  gnome-shell  [kernel.kallsyms]                   [k] static_protections
            |
            --- static_protections
               |
               |--91.80%-- __change_page_attr_set_clr
               |          change_page_attr_set_clr
               |          set_pages_array_wb
               |          |
               |          |--96.55%-- ttm_dma_unpopulate
               |          |          nouveau_ttm_tt_unpopulate
               |          |          ttm_tt_destroy
               |          |          ttm_bo_cleanup_memtype_use
               |          |          ttm_bo_release
               |          |          kref_put
               |          |          ttm_bo_unref
               |          |          nouveau_gem_object_del
               |          |          drm_gem_object_free
               |          |          kref_put
               |          |          drm_gem_object_unreference_unlocked
               |          |          drm_gem_object_handle_unreference_unlocked.part.1
               |          |          drm_gem_handle_delete
               |          |          drm_gem_close_ioctl
               |          |          drm_ioctl
               |          |          do_vfs_ioctl
               |          |          sys_ioctl
               |          |          system_call_fastpath
               |          |          __GI___ioctl
               |          |
               |           --3.45%-- ttm_dma_pages_put
               |                     ttm_dma_page_pool_free
               |                     ttm_dma_unpopulate
               |                     nouveau_ttm_tt_unpopulate
               |                     ttm_tt_destroy
               |                     ttm_bo_cleanup_memtype_use
               |                     ttm_bo_release
               |                     kref_put
               |                     ttm_bo_unref
               |                     nouveau_gem_object_del
               |                     drm_gem_object_free
               |                     kref_put
               |                     drm_gem_object_unreference_unlocked
               |                     drm_gem_object_handle_unreference_unlocked.part.1
               |                     drm_gem_handle_delete
               |                     drm_gem_close_ioctl
               |                     drm_ioctl
               |                     do_vfs_ioctl
               |                     sys_ioctl
               |                     system_call_fastpath
               |                     __GI___ioctl
               |
                --8.20%-- change_page_attr_set_clr
                          set_pages_array_wb
                          |
                          |--93.76%-- ttm_dma_unpopulate
                          |          nouveau_ttm_tt_unpopulate
                          |          ttm_tt_destroy
                          |          ttm_bo_cleanup_memtype_use
                          |          ttm_bo_release
                          |          kref_put
                          |          ttm_bo_unref
                          |          nouveau_gem_object_del
                          |          drm_gem_object_free
                          |          kref_put
                          |          drm_gem_object_unreference_unlocked
                          |          drm_gem_object_handle_unreference_unlocked.part.1
                          |          drm_gem_handle_delete
                          |          drm_gem_close_ioctl
                          |          drm_ioctl
                          |          do_vfs_ioctl
                          |          sys_ioctl
                          |          system_call_fastpath
                          |          __GI___ioctl
                          |
                           --6.24%-- ttm_dma_pages_put
                                     ttm_dma_page_pool_free
                                     ttm_dma_unpopulate
                                     nouveau_ttm_tt_unpopulate
                                     ttm_tt_destroy
                                     ttm_bo_cleanup_memtype_use
                                     ttm_bo_release
                                     kref_put
                                     ttm_bo_unref
                                     nouveau_gem_object_del
                                     drm_gem_object_free
                                     kref_put
                                     drm_gem_object_unreference_unlocked
                                     drm_gem_object_handle_unreference_unlocked.part.1
                                     drm_gem_handle_delete
                                     drm_gem_close_ioctl
                                     drm_ioctl
                                     do_vfs_ioctl
                                     sys_ioctl
                                     system_call_fastpath
                                     __GI___ioctl

and after this patch all of that disappears.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>