drm/i915: Use a separate slab for vmas

vma are more frequently allocated than objects and so should equally
benefit from having a dedicated slab.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 20a6176..a57fdd9 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4612,7 +4612,7 @@
 
 	list_del(&vma->vma_link);
 
-	kfree(vma);
+	kmem_cache_free(to_i915(vma->obj->base.dev)->vmas, vma);
 }
 
 static void
@@ -4991,6 +4991,11 @@
 				  sizeof(struct drm_i915_gem_object), 0,
 				  SLAB_HWCACHE_ALIGN,
 				  NULL);
+	dev_priv->vmas =
+		kmem_cache_create("i915_gem_vma",
+				  sizeof(struct i915_vma), 0,
+				  SLAB_HWCACHE_ALIGN,
+				  NULL);
 	dev_priv->requests =
 		kmem_cache_create("i915_gem_request",
 				  sizeof(struct drm_i915_gem_request), 0,