linux-kernel - Re: [PATCH 10/12] writeback: only allow one inflight and pending full flush

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Message-ID: <CA+55aFw14cHWfcqi_4HpMserCDLX97kbnV2X+L+fio3wRHpkig@mail.gmail.com>
Date:   Thu, 28 Sep 2017 14:44:15 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH 10/12] writeback: only allow one inflight and pending full flush

On Thu, Sep 28, 2017 at 2:41 PM, Andrew Morton
<akpm@...ux-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.

               Linus