Received-SPF: pass (google.com: domain of linux-kernel+bounces-51970-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Precedence: bulk
MIME-Version: 1.0
References: <20240204125404.2112384-1-hezhongkun.hzk@bytedance.com> <Zb_bhO8Z_d7VUCdJ@casper.infradead.org>
In-Reply-To: <Zb_bhO8Z_d7VUCdJ@casper.infradead.org>
From: Zhongkun He <hezhongkun.hzk@bytedance.com>
Date: Mon, 5 Feb 2024 09:08:05 +0800
Message-ID: <CACSyD1MEM+KnNMimmbdSFXOsok9S=vN=DxzS9x90_6+pt5qjFA@mail.gmail.com>
Subject: Re: [External] Re: [PATCH] mm/z3fold: remove unneeded spinlock
To: Matthew Wilcox <willy@infradead.org>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org, 
	linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Mon, Feb 5, 2024 at 2:46=E2=80=AFAM Matthew Wilcox <willy@infradead.org>=
 wrote:
>
> On Sun, Feb 04, 2024 at 08:54:04PM +0800, Zhongkun He wrote:
> > There is no need to use spinlock in this section, so
> > remove it.
>
> I don't know this code at all, but the idiom is (relatively) common.
> It waits until anybody _currently_ holding the lock has released it.
>
> That would, eg, make it safe to free the 'pool' memory.
>
> > -     spin_lock(&pool->lock);
> > -     spin_unlock(&pool->lock);
>

no,  please see the commit 'e774a7bc7f0adb'.

        spin_lock(&pool->lock);
-       if (!list_empty(&page->lru))
-               list_del_init(&page->lru);
        spin_unlock(&pool->lock);

The original purpose of this lock was to protect  page->lru,
which was removed now, so the spinlock is unnecessary.

Thanks for your time.