drm/i915: wire up shrinkctl->nr_scanned

shrink_slab() allows us to report back the number of objects we
successfully scanned (out of the target shrinkctl->nr_to_scan).  As
report the number of pages owned by each GEM object as a separate item
to the shrinker, we cannot precisely control the number of shrinker
objects we scan on each pass; and indeed may free more than requested.
If we fail to tell the shrinker about the number of objects we process,
it will continue to hold a grudge against us as any objects left
unscanned are added to the next reclaim -- and so we will keep on
"unfairly" shrinking our own slab in comparison to other slabs.

Link: http://lkml.kernel.org/r/20170822135325.9191-2-chris@chris-wilson.co.uk
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Shaohua Li <shli@fb.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -4308,10 +4308,10 @@ i915_drop_caches_set(void *data, u64 val)
 
 	fs_reclaim_acquire(GFP_KERNEL);
 	if (val & DROP_BOUND)
-		i915_gem_shrink(dev_priv, LONG_MAX, I915_SHRINK_BOUND);
+		i915_gem_shrink(dev_priv, LONG_MAX, NULL, I915_SHRINK_BOUND);
 
 	if (val & DROP_UNBOUND)
-		i915_gem_shrink(dev_priv, LONG_MAX, I915_SHRINK_UNBOUND);
+		i915_gem_shrink(dev_priv, LONG_MAX, NULL, I915_SHRINK_UNBOUND);
 
 	if (val & DROP_SHRINK_ALL)
 		i915_gem_shrink_all(dev_priv);

drivers/gpu/drm/i915/i915_drv.h

@@ -3742,6 +3742,7 @@ i915_gem_object_create_internal(struct drm_i915_private *dev_priv,
 /* i915_gem_shrinker.c */
 unsigned long i915_gem_shrink(struct drm_i915_private *dev_priv,
 			      unsigned long target,
+			      unsigned long *nr_scanned,
 			      unsigned flags);
 #define I915_SHRINK_PURGEABLE 0x1
 #define I915_SHRINK_UNBOUND 0x2

drivers/gpu/drm/i915/i915_gem.c

@@ -2354,7 +2354,7 @@ rebuild_st:
 				goto err_sg;
 			}
 
-			i915_gem_shrink(dev_priv, 2 * page_count, *s++);
+			i915_gem_shrink(dev_priv, 2 * page_count, NULL, *s++);
 			cond_resched();
 
 			/* We've tried hard to allocate the memory by reaping
@@ -5015,7 +5015,7 @@ int i915_gem_freeze_late(struct drm_i915_private *dev_priv)
 	 * the objects as well, see i915_gem_freeze()
 	 */
 
-	i915_gem_shrink(dev_priv, -1UL, I915_SHRINK_UNBOUND);
+	i915_gem_shrink(dev_priv, -1UL, NULL, I915_SHRINK_UNBOUND);
 	i915_gem_drain_freed_objects(dev_priv);
 
 	mutex_lock(&dev_priv->drm.struct_mutex);

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -2062,7 +2062,7 @@ int i915_gem_gtt_prepare_pages(struct drm_i915_gem_object *obj,
 		 */
 		GEM_BUG_ON(obj->mm.pages == pages);
 	} while (i915_gem_shrink(to_i915(obj->base.dev),
-				 obj->base.size >> PAGE_SHIFT,
+				 obj->base.size >> PAGE_SHIFT, NULL,
 				 I915_SHRINK_BOUND |
 				 I915_SHRINK_UNBOUND |
 				 I915_SHRINK_ACTIVE));

drivers/gpu/drm/i915/i915_gem_shrinker.c

@@ -136,6 +136,7 @@ static bool unsafe_drop_pages(struct drm_i915_gem_object *obj)
  * i915_gem_shrink - Shrink buffer object caches
  * @dev_priv: i915 device
  * @target: amount of memory to make available, in pages
+ * @nr_scanned: optional output for number of pages scanned (incremental)
  * @flags: control flags for selecting cache types
  *
  * This function is the main interface to the shrinker. It will try to release
@@ -158,7 +159,9 @@ static bool unsafe_drop_pages(struct drm_i915_gem_object *obj)
  */
 unsigned long
 i915_gem_shrink(struct drm_i915_private *dev_priv,
-		unsigned long target, unsigned flags)
+		unsigned long target,
+		unsigned long *nr_scanned,
+		unsigned flags)
 {
 	const struct {
 		struct list_head *list;
@@ -169,6 +172,7 @@ i915_gem_shrink(struct drm_i915_private *dev_priv,
 		{ NULL, 0 },
 	}, *phase;
 	unsigned long count = 0;
+	unsigned long scanned = 0;
 	bool unlock;
 
 	if (!shrinker_lock(dev_priv, &unlock))
@@ -249,6 +253,7 @@ i915_gem_shrink(struct drm_i915_private *dev_priv,
 					count += obj->base.size >> PAGE_SHIFT;
 				}
 				mutex_unlock(&obj->mm.lock);
+				scanned += obj->base.size >> PAGE_SHIFT;
 			}
 		}
 		list_splice_tail(&still_in_list, phase->list);
@@ -261,6 +266,8 @@ i915_gem_shrink(struct drm_i915_private *dev_priv,
 
 	shrinker_unlock(dev_priv, unlock);
 
+	if (nr_scanned)
+		*nr_scanned += scanned;
 	return count;
 }
 
@@ -283,7 +290,7 @@ unsigned long i915_gem_shrink_all(struct drm_i915_private *dev_priv)
 	unsigned long freed;
 
 	intel_runtime_pm_get(dev_priv);
-	freed = i915_gem_shrink(dev_priv, -1UL,
+	freed = i915_gem_shrink(dev_priv, -1UL, NULL,
 				I915_SHRINK_BOUND |
 				I915_SHRINK_UNBOUND |
 				I915_SHRINK_ACTIVE);
@@ -329,23 +336,28 @@ i915_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 	unsigned long freed;
 	bool unlock;
 
+	sc->nr_scanned = 0;
+
 	if (!shrinker_lock(dev_priv, &unlock))
 		return SHRINK_STOP;
 
 	freed = i915_gem_shrink(dev_priv,
 				sc->nr_to_scan,
+				&sc->nr_scanned,
 				I915_SHRINK_BOUND |
 				I915_SHRINK_UNBOUND |
 				I915_SHRINK_PURGEABLE);
 	if (freed < sc->nr_to_scan)
 		freed += i915_gem_shrink(dev_priv,
-					 sc->nr_to_scan - freed,
+					 sc->nr_to_scan - sc->nr_scanned,
+					 &sc->nr_scanned,
 					 I915_SHRINK_BOUND |
 					 I915_SHRINK_UNBOUND);
 	if (freed < sc->nr_to_scan && current_is_kswapd()) {
 		intel_runtime_pm_get(dev_priv);
 		freed += i915_gem_shrink(dev_priv,
-					 sc->nr_to_scan - freed,
+					 sc->nr_to_scan - sc->nr_scanned,
+					 &sc->nr_scanned,
 					 I915_SHRINK_ACTIVE |
 					 I915_SHRINK_BOUND |
 					 I915_SHRINK_UNBOUND);
@@ -354,7 +366,7 @@ i915_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 
 	shrinker_unlock(dev_priv, unlock);
 
-	return freed;
+	return sc->nr_scanned ? freed : SHRINK_STOP;
 }
 
 static bool
@@ -453,7 +465,7 @@ i915_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr
 		goto out;
 
 	intel_runtime_pm_get(dev_priv);
-	freed_pages += i915_gem_shrink(dev_priv, -1UL,
+	freed_pages += i915_gem_shrink(dev_priv, -1UL, NULL,
 				       I915_SHRINK_BOUND |
 				       I915_SHRINK_UNBOUND |
 				       I915_SHRINK_ACTIVE |