How to interpret address_space struct in `# define __percpu __attribute__((noderef, address_space(3)))`

问题

I am looking scheduling algorithm in

static void __sched notrace __schedule(bool preempt) (__schedule)

Along the way, I find # define __percpu __attribute__((noderef, address_space(3))) (address_space)

However, I cannot understand why struct address_space can be initialized by using round brackets( ) since I look through struct syntax in c language.

How to initialize a struct in accordance with C programming language standards. struct should be initialized by { } for each filed.

So, what does address_space(3) mean?

来源：https://stackoverflow.com/questions/46591635/how-to-interpret-address-space-struct-in-define-percpu-attribute-noder