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Date:   Fri, 31 Aug 2018 08:58:39 -0700
From:   Dave Hansen <>
To:     Yu-cheng Yu <>,
        Peter Zijlstra <>,
        Jann Horn <>
Cc:     the arch/x86 maintainers <>,
        "H . Peter Anvin" <>,
        Thomas Gleixner <>,
        Ingo Molnar <>,
        kernel list <>,, Linux-MM <>,
        linux-arch <>,
        Linux API <>,
        Arnd Bergmann <>,
        Andy Lutomirski <>,
        Balbir Singh <>,
        Cyrill Gorcunov <>,
        Florian Weimer <>,,
        Jonathan Corbet <>,,
        Mike Kravetz <>,
        Nadav Amit <>,
        Oleg Nesterov <>, Pavel Machek <>,,
Subject: Re: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and
 pmdp_set_wrprotect for _PAGE_DIRTY_SW

On 08/31/2018 08:48 AM, Yu-cheng Yu wrote:
> To trigger a race in ptep_set_wrprotect(), we need to fork from one of
> three pthread siblings.
> Or do we measure only how much this affects fork?
> If there is no racing, the effect should be minimal.

We don't need a race.

I think the cmpxchg will be slower, even without a race, than the code
that was there before.  The cmpxchg is a simple, straightforward
solution, but we're putting it in place of a plain memory write, which
is suboptimal.

But, before I nitpick the performance, I wanted to see if we could even
detect a delta.

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