[PATCH 7/8] drm/i915/ttm: make evicted shmem pages visible to the shrinker

[Matthew Auld]

We currently just evict lmem objects to system memory when under memory
pressure. For this case we lack the usual object mm.pages, which
effectively hides the pages from the i915-gem shrinker, until we
actually "attach" the TT to the object, or in the case of lmem-only
objects it just gets migrated back the lmem. For such cases we can make
the object visible as soon as we populate the TT with shmem pages, and
then hide it again when doing the unpopulate.

Signed-off-by: Matthew Auld <matthew.auld at intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_object.h   |  1 +
 drivers/gpu/drm/i915/gem/i915_gem_shrinker.c | 21 +++++++++++++-------
 drivers/gpu/drm/i915/gem/i915_gem_ttm.c      | 13 ++++++++++++
 3 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
index 305caded7a2a..c88b881a6b98 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
@@ -540,6 +540,7 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
 
 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_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)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
index ea5811f38e0d..6fa2db4fe8c9 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
@@ -469,13 +469,12 @@ void i915_gem_object_make_unshrinkable(struct drm_i915_gem_object *obj)
 	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)
+static void ___i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj,
+					       struct list_head *head)
 {
 	struct drm_i915_private *i915 = obj_to_i915(obj);
 	unsigned long flags;
 
-	GEM_BUG_ON(!i915_gem_object_has_pages(obj));
 	if (!i915_gem_object_is_shrinkable(obj))
 		return;
 
@@ -494,14 +493,22 @@ static void __i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj,
 	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_shrinkable(struct drm_i915_gem_object *obj)
 {
-	__i915_gem_object_make_shrinkable(obj,
-					  &obj_to_i915(obj)->mm.shrink_list);
+	GEM_BUG_ON(!i915_gem_object_has_pages(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);
+	GEM_BUG_ON(!i915_gem_object_has_pages(obj));
+	___i915_gem_object_make_shrinkable(obj,
+					   &obj_to_i915(obj)->mm.purge_list);
 }
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
index 50df890f7b68..992581ef1297 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
@@ -227,6 +227,17 @@ static int i915_ttm_tt_shmem_populate(struct ttm_device *bdev,
 	if (ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)
 		ttm->page_flags &= ~TTM_PAGE_FLAG_SWAPPED;
 
+	GEM_BUG_ON(obj->mm.madv != I915_MADV_WILLNEED);
+
+	/*
+	 * Even if we lack mm.pages for this object(which will be the case when
+	 * something is evicted to system memory by TTM), we still want to make
+	 * this object visible to the shrinker, since the underlying ttm_tt
+	 * still has the real shmem pages. When unpopulating the tt(possibly due
+	 * to shrinking) we hide it again from the shrinker.
+	 */
+	__i915_gem_object_make_shrinkable(obj);
+
 	i915_tt->cached_st = st;
 	return 0;
 
@@ -241,6 +252,8 @@ static void i915_ttm_tt_shmem_unpopulate(struct ttm_tt *ttm)
 	struct drm_i915_gem_object *obj = i915_tt->obj;
 	bool backup = ttm->page_flags & TTM_PAGE_FLAG_SWAPPED;
 
+	i915_gem_object_make_unshrinkable(obj);
+
 	if (obj->mm.madv == I915_MADV_DONTNEED)
 		obj->mm.dirty = false;
 
-- 
2.26.3