Subject: Re: [PATCH 10/12] writeback: only allow one inflight and pending full
 flush
To: Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>, Jan Kara <jack@suse.cz>
References: <1506543239-31470-1-git-send-email-axboe@kernel.dk>
 <1506543239-31470-11-git-send-email-axboe@kernel.dk>
 <20170928144100.e11801ef742521e0e3f4b8df@linux-foundation.org>
 <CA+55aFw14cHWfcqi_4HpMserCDLX97kbnV2X+L+fio3wRHpkig@mail.gmail.com>
From: Jens Axboe <axboe@kernel.dk>
Message-ID: <552d4502-0b0a-87fc-7b16-6b322c3af3ed@kernel.dk>
Date: Fri, 29 Sep 2017 02:17:32 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.3.0
MIME-Version: 1.0
In-Reply-To: <CA+55aFw14cHWfcqi_4HpMserCDLX97kbnV2X+L+fio3wRHpkig@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 873
Lines: 24

On 09/28/2017 11:44 PM, Linus Torvalds wrote:
> On Thu, Sep 28, 2017 at 2:41 PM, Andrew Morton
> <akpm@linux-foundation.org> wrote:
>>
>> test_and_set_bit()?
> 
> If there aren't any atomicity concerns (either because of higher-level
> locking, or because racing and having two people set the bit is fine),
> it can be better to do them separately if the test_bit() is the common
> case and you can avoid dirtying a cacheline that way.
> 
> But yeah, if that is the case, it might be worth documenting, because
> test_and_set_bit() is the more obviously appropriate "there can be
> only one" model.

It is documented though, but maybe not well enough...

I've actually had to document/explain it enough times now, that it
might be worth making a general construct. Though it has to be
used carefully, so perhaps it's better contained as separate use
cases.

-- 
Jens Axboe