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From: Konstantin Khlebnikov <koct9i@gmail.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
	linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Michal Hocko <mhocko@suse.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v2] mm/huge_memory.c: reorder operations in __split_huge_page_tail()
Date: Sun, 11 Feb 2018 18:32:10 +0300
Message-ID: <CALYGNiMjuW4BM2tSUOUmJUu7kX0HEL1EN-YFi=cvtstQi3YeHQ@mail.gmail.com> (raw)
In-Reply-To: <20180211151433.xvza2mugfybyocoi@node.shutemov.name>

On Sun, Feb 11, 2018 at 6:14 PM, Kirill A. Shutemov
<kirill@shutemov.name> 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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Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-11 10:35 [PATCH] mm/huge_memory.c: split should clone page flags before unfreezing pageref Konstantin Khlebnikov
2018-02-11 11:07 ` Kirill A. Shutemov
2018-02-11 13:13   ` Konstantin Khlebnikov
2018-02-11 14:29     ` [PATCH v2] mm/huge_memory.c: reorder operations in __split_huge_page_tail() Konstantin Khlebnikov
2018-02-11 15:14       ` Kirill A. Shutemov
2018-02-11 15:32         ` Konstantin Khlebnikov [this message]
2018-02-11 15:47           ` Kirill A. Shutemov
2018-02-11 15:55             ` Konstantin Khlebnikov
2018-02-11 20:09       ` Matthew Wilcox
2018-02-12 13:58     ` [PATCH v3 1/2] mm/page_ref: use atomic_set_release in page_ref_unfreeze Konstantin Khlebnikov
2018-02-12 14:07       ` Kirill A. Shutemov
2018-02-12 13:58     ` [PATCH v3 2/2] mm/huge_memory.c: reorder operations in __split_huge_page_tail() Konstantin Khlebnikov
2018-02-12 14:11       ` Kirill A. Shutemov

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