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Subject: Re: [PATCH 1/8] membarrier: Document why membarrier() works
To:     Peter Zijlstra <peterz@infradead.org>,
        Nicholas Piggin <npiggin@gmail.com>
Cc:     x86@kernel.org, Andrew Morton <akpm@linux-foundation.org>,
        Dave Hansen <dave.hansen@intel.com>,
        LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
References: <cover.1623813516.git.luto@kernel.org>
 <b648efcb72feb257b9fe004bd132f581805ec0d6.1623813516.git.luto@kernel.org>
 <1623814509.xcl6pmt93d.astroid@bobo.none>
 <YMmoqgLdMNu7KAV5@hirez.programming.kicks-ass.net>
From:   Andy Lutomirski <luto@kernel.org>
Message-ID: <b7102c74-18b0-150e-c103-85afa26a8b6a@kernel.org>
Date:   Thu, 17 Jun 2021 16:45:44 -0700
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On 6/16/21 12:30 AM, Peter Zijlstra wrote:
> On Wed, Jun 16, 2021 at 02:00:37PM +1000, Nicholas Piggin wrote:
>> Excerpts from Andy Lutomirski's message of June 16, 2021 1:21 pm:
>>> We had a nice comment at the top of membarrier.c explaining why membarrier
>>> worked in a handful of scenarios, but that consisted more of a list of
>>> things not to forget than an actual description of the algorithm and why it
>>> should be expected to work.
>>>
>>> Add a comment explaining my understanding of the algorithm.  This exposes a
>>> couple of implementation issues that I will hopefully fix up in subsequent
>>> patches.
>>>
>>> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
>>> Cc: Nicholas Piggin <npiggin@gmail.com>
>>> Cc: Peter Zijlstra <peterz@infradead.org>
>>> Signed-off-by: Andy Lutomirski <luto@kernel.org>
>>> ---
>>>  kernel/sched/membarrier.c | 55 +++++++++++++++++++++++++++++++++++++++
>>>  1 file changed, 55 insertions(+)
>>>
>>> diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
>>> index b5add64d9698..3173b063d358 100644
>>> --- a/kernel/sched/membarrier.c
>>> +++ b/kernel/sched/membarrier.c
>>> @@ -7,6 +7,61 @@
>>>  #include "sched.h"
>>>  
>>
>> Precisely describing the orderings is great, not a fan of the style of the
>> comment though.
> 
> I'm with Nick on that; I can't read it :/ It only makes things more
> confusing. If you want precision, English (or any natural language) is
> your enemy.
> 
> To describe ordering use the diagrams and/or litmus tests.
> 

I made some changes.  Maybe it's better now.