Re: [PATCH 03/10] hugetlb: Use LIST_HEAD() to define a list head

[Miaohe Lin]

On 2022/8/27 10:48, Muchun Song wrote:
> 
> 
>> On Aug 27, 2022, at 10:27, Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:
>>
>> On 2022/8/27 9:47, Muchun Song wrote:
>>>
>>>
>>>> On Aug 26, 2022, at 17:24, Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:
>>>>
>>>> We can avoid unneeded WRITE_ONCE() overhead by using LIST_HEAD() to define
>>>> a list head.
>>>
>>> IIUC, the overhead doesn’t change. Right?
>>
>> I think the overhead is changed. LIST_HEAD is initialized without using WRITE_ONCE():
> 
> I think there is no special difference with "WRITE_ONCE(var, 0)" vs "var = 0” in

It's not write var to 0 indeed. But there seems are no special difference.

> assembly code. Both code of line will be compiled to a mov or movq instruction.
> I didn’t confirm if the assembly code is different (I tend to think it is similar).
> Just some analysis from me.

I checked the generated code in x86, they're almost same. And in aarch64, there's difference
between one "stp" instruction vs two "str" instruction. So I think you're right. Thanks for
pointing this out. I should tweak the commit log in next version.

Thanks a lot,
Miaohe Lin