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Subject: Re: [PATCH] buffer: Avoid setting buffer bits that are already set
To: kemi <kemi.wang@intel.com>, Andi Kleen <ak@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>, Darrick J Wong <darrick.wong@oracle.com>,
        Eric Biggers <ebiggers@google.com>,
        Andreas Gruenbacher <agruenba@redhat.com>,
        Jeff Layton <jlayton@redhat.com>, Dave <dave.hansen@linux.intel.com>,
        Andi Kleen <andi.kleen@intel.com>, Tim Chen <tim.c.chen@intel.com>,
        Ying Huang <ying.huang@intel.com>, Aaron Lu <aaron.lu@intel.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>
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From: Jens Axboe <axboe@kernel.dk>
Message-ID: <5677e6be-38ab-edb3-36db-094452c61d1e@kernel.dk>
Date: Tue, 24 Oct 2017 07:50:27 -0600
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On 10/23/2017 07:25 PM, kemi wrote:
> 
> 
> On 2017年10月24日 09:21, Andi Kleen wrote:
>> kemi <kemi.wang@intel.com> writes:
>>>
>>> I'll see if I can find some
>>>> time to implement the above in a nice way.
>>>
>>> Agree. Maybe something like test_and_set_bit() would be more suitable.
>>
>> test_and_set_bit is a very different operation for the CPU because
>> it is atomic for both. But we want the initial read to not
>> be atomic.
>>
> 
> I meant to express the meaning of test before setting bit.
> Apologize to make you confused.

That's why I suggested something like set_bit_if_not_set(),
test_and_set_bit() is both already used and has entirely
different semantics.

-- 
Jens Axboe