drm/ttm: Make NO_EVICT bos available to shrinkers pending destruction

NO_EVICT bos that are not idle when all references are dropped are put on
the delayed destroy list. However, since they are not on LRU lists, they
are not available to shrinkers at that point, and buffers on the delayed
destroy list are not checked very often for idle.

So when these buffers are put on the delayed destroy list, clear the
NO_EVICT flag and put them on the right LRU list. This way they are
immediately available for eviction or shrinkers and will not cause false
OOMS.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>

drivers/gpu/drm/ttm/ttm_bo.c

@@ -429,8 +429,20 @@ static void ttm_bo_cleanup_refs_or_queue(struct ttm_buffer_object *bo)
 		sync_obj = driver->sync_obj_ref(bo->sync_obj);
 	spin_unlock(&bdev->fence_lock);
 
-	if (!ret)
+	if (!ret) {
+
+		/*
+		 * Make NO_EVICT bos immediately available to
+		 * shrinkers, now that they are queued for
+		 * destruction.
+		 */
+		if (bo->mem.placement & TTM_PL_FLAG_NO_EVICT) {
+			bo->mem.placement &= ~TTM_PL_FLAG_NO_EVICT;
+			ttm_bo_add_to_lru(bo);
+		}
+
 		ww_mutex_unlock(&bo->resv->lock);
+	}
 
 	kref_get(&bo->list_kref);
 	list_add_tail(&bo->ddestroy, &bdev->ddestroy);