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

1 files changed, 9 insertions, 8 deletions

diff --git a/drivers/gpu/drm/i915/gt/intel_ringbuffer.c b/drivers/gpu/drm/i915/gt/intel_ringbuffer.c
index 8d24a49e5139..aa2f06b80961 100644
--- a/drivers/gpu/drm/i915/gt/intel_ringbuffer.c
+++ b/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);
 }