drm/i915: Remove walk over obj->vma_list for the shrinker

In the next patch, we want to reduce the lock coverage within the
shrinker, and one of the dangerous walks we have is over obj->vma_list.
We are only walking the obj->vma_list in order to check whether it has
been permanently pinned by HW access, typically via use on the scanout.
But we have a couple of other long term pins, the context objects for
which we currently have to check the individual vma pin_count. If we
instead mark these using obj->pin_display, we can forgo the dangerous
and sometimes slow list iteration.

v2: Rearrange code to try and avoid confusion from false associations
due to arrangement of whitespace along with rebasing on obj->pin_global.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171013202621.7276-4-chris@chris-wilson.co.uk

1 files changed, 7 insertions, 20 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
index b5c87d89777b..575a6b735f39 100644
--- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
@@ -71,25 +71,6 @@ static void shrinker_unlock(struct drm_i915_private *dev_priv, bool unlock)
 	mutex_unlock(&dev_priv->drm.struct_mutex);
 }
 
-static bool any_vma_pinned(struct drm_i915_gem_object *obj)
-{
-	struct i915_vma *vma;
-
-	list_for_each_entry(vma, &obj->vma_list, obj_link) {
-		/* Only GGTT vma may be permanently pinned, and are always
-		 * at the start of the list. We can stop hunting as soon
-		 * as we see a ppGTT vma.
-		 */
-		if (!i915_vma_is_ggtt(vma))
-			break;
-
-		if (i915_vma_is_pinned(vma))
-			return true;
-	}
-
-	return false;
-}
-
 static bool swap_available(void)
 {
 	return get_nr_swap_pages() > 0;
@@ -115,7 +96,13 @@ static bool can_release_pages(struct drm_i915_gem_object *obj)
 	if (atomic_read(&obj->mm.pages_pin_count) > obj->bind_count)
 		return false;
 
-	if (any_vma_pinned(obj))
+	/* If any vma are "permanently" pinned, it will prevent us from
+	 * reclaiming the obj->mm.pages. We only allow scanout objects to claim
+	 * a permanent pin, along with a few others like the context objects.
+	 * To simplify the scan, and to avoid walking the list of vma under the
+	 * object, we just check the count of its permanently pinned.
+	 */
+	if (obj->pin_global)
 		return false;
 
 	/* We can only return physical pages to the system if we can either