linux-kernel - Re: [PATCH v2] mm/huge_memory.c: reorder operations in __split_huge_page

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Message-ID: <20180211151433.xvza2mugfybyocoi@node.shutemov.name>
Date:   Sun, 11 Feb 2018 18:14:33 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Nicholas Piggin <npiggin@...il.com>
Subject: Re: [PATCH v2] mm/huge_memory.c: reorder operations in
 __split_huge_page_tail()

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.

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