drm/i915: mark a newly-created GEM object dirty when filled with data

When creating a new (pageable) GEM object and filling it with data, we
must mark it as 'dirty', i.e. backing store is out-of-date w.r.t. the
newly-written content. This ensures that if the object is evicted under
memory pressure, its pages in the pagecache will be written to backing
store rather than discarded.

Based on an original version by Alex Dai.
Signed-off-by: NAlex Dai <yu.dai@intel.com>
Signed-off-by: NDave Gordon <david.s.gordon@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1449773486-30822-3-git-send-email-david.s.gordon@intel.comReviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -5225,6 +5225,7 @@ i915_gem_object_create_from_data(struct drm_device *dev,
 	i915_gem_object_pin_pages(obj);
 	sg = obj->pages;
 	bytes = sg_copy_from_buffer(sg->sgl, sg->nents, (void *)data, size);
+	obj->dirty = 1;		/* Backing store is now out of date */
 	i915_gem_object_unpin_pages(obj);
 
 	if (WARN_ON(bytes != size)) {