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

[Konstantin Khlebnikov]

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,

>
> You need at least explain why it's safe now.
>
> I would rather leave page_ref_inc()/page_ref_add() + explcit
> smp_mb__before_atomic().
>
> --
>  Kirill A. Shutemov
>
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