Re: [PATCH v2] mm/huge_memory.c: reorder operations in __split_huge_page_tail()

[Konstantin Khlebnikov]

On Sun, Feb 11, 2018 at 6:47 PM, Kirill A. Shutemov
<kirill@xxxxxxxxxxxxx> wrote:
> On Sun, Feb 11, 2018 at 06:32:10PM +0300, Konstantin Khlebnikov wrote:
>> On Sun, Feb 11, 2018 at 6:14 PM, Kirill A. Shutemov
>> <kirill@xxxxxxxxxxxxx> wrote:
>> > On Sun, Feb 11, 2018 at 05:29:37PM +0300, Konstantin Khlebnikov wrote:
>> >> And replace page_ref_inc()/page_ref_add() with page_ref_unfreeze() which
>> >> is made especially for that and has semantic of smp_store_release().
>> >
>> > Nak on this part.
>> >
>> > page_ref_unfreeze() uses atomic_set() which neglects the situation in the
>> > comment you're removing.
>>
>> Why? look into x86 smp_store_release
>> for PPro it use same sequence smp_wb + WRITE_ONCE
>> As I see spin_unlock uses exactly this macro.
>>
>> Anyway if page_ref_unfreeze cannot handle races with
>> get_page_unless_zero() then it completely useless,
>
> Okay, fair enough.
>
> But please call it out it the commit message.

OK, I'll review this yet again and resend tomorrow.