Re: [PATCH] locking/local_lock: Make the empty local_lock_*() function a macro.

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2022-01-05 22:34:31 [-0500], Waiman Long wrote:
> 
> I try out this patch and it indeed helps to reduce the object size of
> functions that use local_lock(). However, the extra code isn't an additional
> mov+add.
> 
> Using folio_add_lru() as an example,
> 
> Without the patch:
> 
> 466        local_lock(&lru_pvecs.lock);
>    0x00000000000032ee <+14>:    mov    $0x1,%edi
>    0x00000000000032f3 <+19>:    callq  0x32f8 <folio_add_lru+24>
>    0x00000000000032f8 <+24>:    callq  0x32fd <folio_add_lru+29>

The call here might be due to some debugging switches or compiler
optimisation. I have with no debug and gcc-11:
| # mm/swap.c:466:     local_lock(&lru_pvecs.lock);
|         movq    $lru_pvecs, %rbx        #, tmp135
|         movq    %rbx, %rax      # tmp135, tcp_ptr__
| #APP
| # 466 "mm/swap.c" 1
|         add %gs:this_cpu_off(%rip), %rax        # this_cpu_off, tcp_ptr__

so it is mov per-CPU variable, add per-CPU offset.

Sebastian