bui := BucketUsageInfo{
			Size:                    uint64(flat.Size),
			VersionsCount:           flat.Versions,
			ObjectsCount:            flat.Objects,
			DeleteMarkersCount:      flat.DeleteMarkers,
			ObjectSizesHistogram:    flat.ObjSizes.toMap(),
			ObjectVersionsHistogram: flat.ObjVersions.toMap(),
		}
		dst[bucket.Name] = bui
	}
	return dst
}

// sizeRecursive returns the path as a flattened entry.