pagecache_write_end
err = pagecache_write_end(obj->base.filp, mapping,
err = pagecache_write_end(obj->base.filp, NULL,
err = pagecache_write_end(file, file->f_mapping,
err = pagecache_write_end(file, NULL,
int pagecache_write_end(struct vm_object *obj, struct address_space *mapping,