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

3 files changed, 16 insertions, 21 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
index b5c87d89777b..575a6b735f39 100644
--- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
+++ b/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
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 766552f2cfae..7f45dd7dc3e5 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/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);
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index b2a6cb09c6e7..8da1bde442dd 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/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);
 }