drm/i915: Hide unshrinkable context objects from the shrinker

The shrinker cannot touch objects used by the contexts (logical state
and ring). Currently we mark those as "pin_global" to let the shrinker
skip over them, however, if we remove them from the shrinker lists
entirely, we don't event have to include them in our shrink accounting.

By keeping the unshrinkable objects in our shrinker tracking, we report
a large number of objects available to be shrunk, and leave the shrinker
deeply unsatisfied when we fail to reclaim those. The shrinker will
persist in trying to reclaim the unavailable objects, forcing the system
into a livelock (not even hitting the dread oomkiller).

v2: Extend unshrinkable protection for perma-pinned scratch and guc
allocations (Tvrtko)
v3: Notice that we should be pinned when marking unshrinkable and so the
link cannot be empty; merge duplicate paths.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190802212137.22207-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_object.c

@@ -63,6 +63,8 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj,
 	spin_lock_init(&obj->vma.lock);
 	INIT_LIST_HEAD(&obj->vma.list);
 
+	INIT_LIST_HEAD(&obj->mm.link);
+
 	INIT_LIST_HEAD(&obj->lut_list);
 	INIT_LIST_HEAD(&obj->batch_pool_link);
 
@@ -273,14 +275,7 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj)
 	 * or else we may oom whilst there are plenty of deferred
 	 * freed objects.
 	 */
-	if (i915_gem_object_has_pages(obj) &&
-	    i915_gem_object_is_shrinkable(obj)) {
-		unsigned long flags;
-
-		spin_lock_irqsave(&i915->mm.obj_lock, flags);
-		list_del_init(&obj->mm.link);
-		spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
-	}
+	i915_gem_object_make_unshrinkable(obj);
 
 	/*
 	 * Since we require blocking on struct_mutex to unbind the freed

drivers/gpu/drm/i915/gem/i915_gem_object.h

@@ -394,6 +394,10 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
 				     unsigned int flags);
 void i915_gem_object_unpin_from_display_plane(struct i915_vma *vma);
 
+void i915_gem_object_make_unshrinkable(struct drm_i915_gem_object *obj);
+void i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj);
+void i915_gem_object_make_purgeable(struct drm_i915_gem_object *obj);
+
 static inline bool cpu_write_needs_clflush(struct drm_i915_gem_object *obj)
 {
 	if (obj->cache_dirty)

drivers/gpu/drm/i915/gem/i915_gem_pages.c

@@ -153,24 +153,13 @@ static void __i915_gem_object_reset_page_iter(struct drm_i915_gem_object *obj)
 struct sg_table *
 __i915_gem_object_unset_pages(struct drm_i915_gem_object *obj)
 {
-	struct drm_i915_private *i915 = to_i915(obj->base.dev);
 	struct sg_table *pages;
 
 	pages = fetch_and_zero(&obj->mm.pages);
 	if (IS_ERR_OR_NULL(pages))
 		return pages;
 
-	if (i915_gem_object_is_shrinkable(obj)) {
-		unsigned long flags;
-
-		spin_lock_irqsave(&i915->mm.obj_lock, flags);
-
-		list_del(&obj->mm.link);
-		i915->mm.shrink_count--;
-		i915->mm.shrink_memory -= obj->base.size;
-
-		spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
-	}
+	i915_gem_object_make_unshrinkable(obj);
 
 	if (obj->mm.mapping) {
 		void *ptr;

drivers/gpu/drm/i915/gem/i915_gem_shrinker.c

@@ -530,3 +530,61 @@ void i915_gem_shrinker_taints_mutex(struct drm_i915_private *i915,
 	if (unlock)
 		mutex_release(&i915->drm.struct_mutex.dep_map, 0, _RET_IP_);
 }
+
+#define obj_to_i915(obj__) to_i915((obj__)->base.dev)
+
+void i915_gem_object_make_unshrinkable(struct drm_i915_gem_object *obj)
+{
+	/*
+	 * We can only be called while the pages are pinned or when
+	 * the pages are released. If pinned, we should only be called
+	 * from a single caller under controlled conditions; and on release
+	 * only one caller may release us. Neither the two may cross.
+	 */
+	if (!list_empty(&obj->mm.link)) { /* pinned by caller */
+		struct drm_i915_private *i915 = obj_to_i915(obj);
+		unsigned long flags;
+
+		spin_lock_irqsave(&i915->mm.obj_lock, flags);
+		GEM_BUG_ON(list_empty(&obj->mm.link));
+
+		list_del_init(&obj->mm.link);
+		i915->mm.shrink_count--;
+		i915->mm.shrink_memory -= obj->base.size;
+
+		spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
+	}
+}
+
+static void __i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj,
+					      struct list_head *head)
+{
+	GEM_BUG_ON(!i915_gem_object_has_pages(obj));
+	GEM_BUG_ON(!list_empty(&obj->mm.link));
+
+	if (i915_gem_object_is_shrinkable(obj)) {
+		struct drm_i915_private *i915 = obj_to_i915(obj);
+		unsigned long flags;
+
+		spin_lock_irqsave(&i915->mm.obj_lock, flags);
+		GEM_BUG_ON(!kref_read(&obj->base.refcount));
+
+		list_add_tail(&obj->mm.link, head);
+		i915->mm.shrink_count++;
+		i915->mm.shrink_memory += obj->base.size;
+
+		spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
+	}
+}
+
+void i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj)
+{
+	__i915_gem_object_make_shrinkable(obj,
+					  &obj_to_i915(obj)->mm.shrink_list);
+}
+
+void i915_gem_object_make_purgeable(struct drm_i915_gem_object *obj)
+{
+	__i915_gem_object_make_shrinkable(obj,
+					  &obj_to_i915(obj)->mm.purge_list);
+}

drivers/gpu/drm/i915/gt/intel_context.c

@@ -118,7 +118,7 @@ static int __context_pin_state(struct i915_vma *vma)
 	 * And mark it as a globally pinned object to let the shrinker know
 	 * it cannot reclaim the object until we release it.
 	 */
-	vma->obj->pin_global++;
+	i915_vma_make_unshrinkable(vma);
 	vma->obj->mm.dirty = true;
 
 	return 0;
@@ -126,8 +126,8 @@ static int __context_pin_state(struct i915_vma *vma)
 
 static void __context_unpin_state(struct i915_vma *vma)
 {
-	vma->obj->pin_global--;
 	__i915_vma_unpin(vma);
+	i915_vma_make_shrinkable(vma);
 }
 
 static void __intel_context_retire(struct i915_active *active)

drivers/gpu/drm/i915/gt/intel_gt.c

@@ -248,7 +248,8 @@ int intel_gt_init_scratch(struct intel_gt *gt, unsigned int size)
 	if (ret)
 		goto err_unref;
 
-	gt->scratch = vma;
+	gt->scratch = i915_vma_make_unshrinkable(vma);
+
 	return 0;
 
 err_unref:

drivers/gpu/drm/i915/gt/intel_ringbuffer.c

@@ -1222,7 +1222,7 @@ int intel_ring_pin(struct intel_ring *ring)
 		goto err_ring;
 	}
 
-	vma->obj->pin_global++;
+	i915_vma_make_unshrinkable(vma);
 
 	GEM_BUG_ON(ring->vaddr);
 	ring->vaddr = addr;
@@ -1251,6 +1251,8 @@ void intel_ring_reset(struct intel_ring *ring, u32 tail)
 
 void intel_ring_unpin(struct intel_ring *ring)
 {
+	struct i915_vma *vma = ring->vma;
+
 	if (!atomic_dec_and_test(&ring->pin_count))
 		return;
 
@@ -1259,18 +1261,17 @@ void intel_ring_unpin(struct intel_ring *ring)
 	/* Discard any unused bytes beyond that submitted to hw. */
 	intel_ring_reset(ring, ring->tail);
 
-	GEM_BUG_ON(!ring->vma);
-	i915_vma_unset_ggtt_write(ring->vma);
-	if (i915_vma_is_map_and_fenceable(ring->vma))
-		i915_vma_unpin_iomap(ring->vma);
+	i915_vma_unset_ggtt_write(vma);
+	if (i915_vma_is_map_and_fenceable(vma))
+		i915_vma_unpin_iomap(vma);
 	else
-		i915_gem_object_unpin_map(ring->vma->obj);
+		i915_gem_object_unpin_map(vma->obj);
 
 	GEM_BUG_ON(!ring->vaddr);
 	ring->vaddr = NULL;
 
-	ring->vma->obj->pin_global--;
-	i915_vma_unpin(ring->vma);
+	i915_vma_unpin(vma);
+	i915_vma_make_purgeable(vma);
 
 	intel_timeline_unpin(ring->timeline);
 }

drivers/gpu/drm/i915/gt/uc/intel_guc.c

@@ -626,7 +626,7 @@ struct i915_vma *intel_guc_allocate_vma(struct intel_guc *guc, u32 size)
 		goto err;
 	}
 
-	return vma;
+	return i915_vma_make_unshrinkable(vma);
 
 err:
 	i915_gem_object_put(obj);

drivers/gpu/drm/i915/i915_debugfs.c

@@ -363,8 +363,9 @@ static int i915_gem_object_info(struct seq_file *m, void *data)
 	struct drm_i915_private *i915 = node_to_i915(m->private);
 	int ret;
 
-	seq_printf(m, "%u shrinkable objects, %llu bytes\n",
+	seq_printf(m, "%u shrinkable [%u free] objects, %llu bytes\n",
 		   i915->mm.shrink_count,
+		   atomic_read(&i915->mm.free_count),
 		   i915->mm.shrink_memory);
 
 	seq_putc(m, '\n');

drivers/gpu/drm/i915/i915_vma.c

@@ -1017,6 +1017,22 @@ int i915_vma_unbind(struct i915_vma *vma)
 	return 0;
 }
 
+struct i915_vma *i915_vma_make_unshrinkable(struct i915_vma *vma)
+{
+	i915_gem_object_make_unshrinkable(vma->obj);
+	return vma;
+}
+
+void i915_vma_make_shrinkable(struct i915_vma *vma)
+{
+	i915_gem_object_make_shrinkable(vma->obj);
+}
+
+void i915_vma_make_purgeable(struct i915_vma *vma)
+{
+	i915_gem_object_make_purgeable(vma->obj);
+}
+
 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
 #include "selftests/i915_vma.c"
 #endif

drivers/gpu/drm/i915/i915_vma.h

@@ -459,4 +459,8 @@ void i915_vma_parked(struct drm_i915_private *i915);
 struct i915_vma *i915_vma_alloc(void);
 void i915_vma_free(struct i915_vma *vma);
 
+struct i915_vma *i915_vma_make_unshrinkable(struct i915_vma *vma);
+void i915_vma_make_shrinkable(struct i915_vma *vma);
+void i915_vma_make_purgeable(struct i915_vma *vma);
+
 #endif