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

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

drivers/gpu/drm/i915/intel_lrc.c

@@ -1093,6 +1093,7 @@ execlists_context_pin(struct intel_engine_cs *engine,
 		i915_ggtt_offset(ce->ring->vma);
 
 	ce->state->obj->mm.dirty = true;
+	ce->state->obj->pin_global++;
 
 	i915_gem_context_get(ctx);
 out:
@@ -1120,6 +1121,7 @@ static void execlists_context_unpin(struct intel_engine_cs *engine,
 
 	intel_ring_unpin(ce->ring);
 
+	ce->state->obj->pin_global--;
 	i915_gem_object_unpin_map(ce->state->obj);
 	i915_vma_unpin(ce->state);
 

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1244,6 +1244,8 @@ int intel_ring_pin(struct intel_ring *ring,
 	if (IS_ERR(addr))
 		goto err;
 
+	vma->obj->pin_global++;
+
 	ring->vaddr = addr;
 	return 0;
 
@@ -1275,6 +1277,7 @@ void intel_ring_unpin(struct intel_ring *ring)
 		i915_gem_object_unpin_map(ring->vma->obj);
 	ring->vaddr = NULL;
 
+	ring->vma->obj->pin_global--;
 	i915_vma_unpin(ring->vma);
 }
 
@@ -1439,6 +1442,7 @@ intel_ring_context_pin(struct intel_engine_cs *engine,
 			goto err;
 
 		ce->state->obj->mm.dirty = true;
+		ce->state->obj->pin_global++;
 	}
 
 	/* The kernel context is only used as a placeholder for flushing the
@@ -1473,8 +1477,10 @@ static void intel_ring_context_unpin(struct intel_engine_cs *engine,
 	if (--ce->pin_count)
 		return;
 
-	if (ce->state)
+	if (ce->state) {
+		ce->state->obj->pin_global--;
 		i915_vma_unpin(ce->state);
+	}
 
 	i915_gem_context_put(ctx);
 }