[PATCH v2] drm/i915: Shrink the GEM kmem_caches upon idling

[Chris Wilson <chris@chris-wilson.co.uk>]

When we finally decide the gpu is idle, that is a good time to shrink
our kmem_caches.

v2: Comment upon the random sprinkling of rcu_barrier() inside the idle
worker.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 335731c93b4a..61b13fdfaa71 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4716,6 +4716,21 @@ i915_gem_retire_work_handler(struct work_struct *work)
 	}
 }
 
+static void shrink_caches(struct drm_i915_private *i915)
+{
+	/*
+	 * kmem_cache_shrink() discards empty slabs and reorders partially
+	 * filled slabs to prioritise allocating from the mostly full slabs,
+	 * with the aim of reducing fragmentation.
+	 */
+	kmem_cache_shrink(i915->priorities);
+	kmem_cache_shrink(i915->dependencies);
+	kmem_cache_shrink(i915->requests);
+	kmem_cache_shrink(i915->luts);
+	kmem_cache_shrink(i915->vmas);
+	kmem_cache_shrink(i915->objects);
+}
+
 static inline bool
 new_requests_since_last_retire(const struct drm_i915_private *i915)
 {
@@ -4803,6 +4818,21 @@ i915_gem_idle_work_handler(struct work_struct *work)
 		GEM_BUG_ON(!dev_priv->gt.awake);
 		i915_queue_hangcheck(dev_priv);
 	}
+
+	/*
+	 * We use magical TYPESAFE_BY_RCU kmem_caches whose pages are not
+	 * returned to the system imediately but only after an RCU grace
+	 * period. We want to encourage such pages to be returned and so
+	 * incorporate a RCU barrier here to provide some rate limiting
+	 * of the driver and flush the old pages before we free a new batch
+	 * from the next round of shrinking.
+	 */
+	rcu_barrier();
+
+	if (!new_requests_since_last_retire(dev_priv)) {
+		__i915_gem_free_work(&dev_priv->mm.free_work);
+		shrink_caches(dev_priv);
+	}
 }
 
 int i915_gem_suspend(struct drm_i915_private *dev_priv)
-- 
2.15.1

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