drm/i915: Split batch pool into size buckets

Now with the trimmed memcpy before the command parser, we try to
allocate many different sizes of batches, predominantly one or two
pages. We can therefore speed up searching for a good sized batch by
keeping the objects of buckets of roughly the same size.

v2: Add a comment about bucket sizes

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index c839b57..6e0a0ae 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1910,7 +1910,7 @@
 	/** Used in execbuf to temporarily hold a ref */
 	struct list_head obj_exec_link;
 
-	struct list_head batch_pool_list;
+	struct list_head batch_pool_link;
 
 	/**
 	 * This is set if the object is on the active lists (has pending