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From: Andi Kleen <ak@linux.intel.com>
To: kemi <kemi.wang@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>, Jan Kara <jack@suse.cz>,
        Darrick J Wong <darrick.wong@oracle.com>,
        Eric Biggers <ebiggers@google.com>,
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        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>
Subject: Re: [PATCH] buffer: Avoid setting buffer bits that are already set
References: <1508772444-27879-1-git-send-email-kemi.wang@intel.com>
        <e2953a84-31d1-fdd2-faf8-62967a9f29c6@kernel.dk>
        <f475ae05-733d-b0a2-cadc-a5913f521153@intel.com>
Date: Mon, 23 Oct 2017 18:21:21 -0700
In-Reply-To: <f475ae05-733d-b0a2-cadc-a5913f521153@intel.com> (kemi's message
        of "Tue, 24 Oct 2017 08:52:22 +0800")
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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.

If you add special functions use a different variant that is only
atomic for the set.

-Andi