drm/i915: Leave vma intact as they are discarded

If we find ourselves trying to reuse a misplaced but active vma, we
currently try to discard it to avoid having to wait to unbind it
(upsetting the current user fo the vma). An alternative to marking it as
a dicarded vma and keeping it in both the obj->vma.list and
obj->vma.tree, is to simply remove it from the lookup rbtree.

While it remains in the list of vma, it will be unbound under eviction
pressure and freed along with the object. We will never reuse it again
for new instances. As before, with no pruning, the list may continually
grow, but eventually we will have the most constrained version of the
ggtt view that meets all requirements -- so the list of vma should not
grow without bound.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2012
Fixes: 9bdcaa5e3a2f ("drm/i915: Discard a misplaced GGTT vma")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200611180421.23262-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 41553e9e57a9e5595d7ce81c5f1465a066b19c22..9aa3066cb75d901e22f733530e424088eb563bce 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -933,44 +933,16 @@ void i915_gem_runtime_suspend(struct drm_i915_private *i915)
        }
 }
 
-static bool
-discard_ggtt_vma(struct i915_vma *vma, const struct i915_ggtt_view *view)
+static void discard_ggtt_vma(struct i915_vma *vma)
 {
-       const struct i915_ggtt_view discard = {
-               .type = I915_GGTT_VIEW_PARTIAL,
-       };
        struct drm_i915_gem_object *obj = vma->obj;
 
        spin_lock(&obj->vma.lock);
-       if (i915_vma_compare(vma, vma->vm, &discard)) {
-               struct rb_node *rb, **p;
-
+       if (!RB_EMPTY_NODE(&vma->obj_node)) {
                rb_erase(&vma->obj_node, &obj->vma.tree);
-               vma->ggtt_view = discard;
-               GEM_BUG_ON(i915_vma_compare(vma, vma->vm, &discard));
-               GEM_BUG_ON(i915_vma_compare(vma, vma->vm, view) == 0);
-
-               rb = NULL;
-               p = &obj->vma.tree.rb_node;
-               while (*p) {
-                       struct i915_vma *pos;
-                       long cmp;
-
-                       rb = *p;
-                       pos = rb_entry(rb, struct i915_vma, obj_node);
-
-                       cmp = i915_vma_compare(pos, vma->vm, &discard);
-                       if (cmp < 0)
-                               p = &rb->rb_right;
-                       else
-                               p = &rb->rb_left;
-               }
-               rb_link_node(&vma->obj_node, rb, p);
-               rb_insert_color(&vma->obj_node, &obj->vma.tree);
+               RB_CLEAR_NODE(&vma->obj_node);
        }
        spin_unlock(&obj->vma.lock);
-
-       return i915_vma_compare(vma, vma->vm, view);
 }
 
 struct i915_vma *
@@ -1035,8 +1007,8 @@ new_vma:
                }
 
                if (i915_vma_is_pinned(vma) || i915_vma_is_active(vma)) {
-                       if (discard_ggtt_vma(vma, view))
-                               goto new_vma;
+                       discard_ggtt_vma(vma);
+                       goto new_vma;
                }
 
                ret = i915_vma_unbind(vma);

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index 9b30ddc49e4bcac8960267e3e99b2635a57bffed..1f63c4a1f055a323e754cd2718a8aaff7e1b8a5b 100644 (file)
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -1087,7 +1087,8 @@ void i915_vma_release(struct kref *ref)
 
                spin_lock(&obj->vma.lock);
                list_del(&vma->obj_link);
-               rb_erase(&vma->obj_node, &obj->vma.tree);
+               if (!RB_EMPTY_NODE(&vma->obj_node))
+                       rb_erase(&vma->obj_node, &obj->vma.tree);
                spin_unlock(&obj->vma.lock);
        }