[Intel-gfx] [PATCH] drm/i915: Only free the oldest stale object before a fresh allocation

[Chris Wilson]

Inspired by Tvrtko's critique of the reaping of the stale contexts
before allocating a new one, also limit the freed object reaping to the
oldest stale object before allocating a fresh object. Unlike contexts,
objects may have radically different sizes of backing storage, but
similar to contexts, whilst we want to prevent starvation due to
excessive freed lists, we also want do not want to delay fresh
allocations for too long. Only freeing the oldest on the freed object
list before each allocation is a reasonable compromise.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/i915_gem.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 91145c39cd43..2048532c9cae 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4473,9 +4473,13 @@ static void i915_gem_flush_free_objects(struct drm_i915_private *i915)
 {
 	struct llist_node *freed;
 
-	freed = llist_del_all(&i915->mm.free_list);
-	if (unlikely(freed))
+	freed = NULL;
+	if (!llist_empty(&i915->mm.free_list))
+		freed = llist_del_first(&i915->mm.free_list);
+	if (unlikely(freed)) {
+		freed->next = NULL;
 		__i915_gem_free_objects(i915, freed);
+	}
 }
 
 static void __i915_gem_free_work(struct work_struct *work)
-- 
2.13.2