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Subject: Re: [PATCH] f2fs: change to use rwsem for cp_mutex
To:     David Laight <David.Laight@ACULAB.COM>,
        'Sahitya Tummala' <stummala@codeaurora.org>,
        Jaegeuk Kim <jaegeuk@kernel.org>,
        "linux-f2fs-devel@lists.sourceforge.net" 
        <linux-f2fs-devel@lists.sourceforge.net>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <1606109312-1944-1-git-send-email-stummala@codeaurora.org>
 <7f5213fb9b334d1290f019ab8ed6ee71@AcuMS.aculab.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <a1b9a134-97a8-6fb7-2fdc-d4de91dff849@huawei.com>
Date:   Tue, 24 Nov 2020 11:12:14 +0800
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On 2020/11/24 1:05, David Laight wrote:
> From: Sahitya Tummala
>> Sent: 23 November 2020 05:29
>>
>> Use rwsem to ensure serialization of the callers and to avoid
>> starvation of high priority tasks, when the system is under
>> heavy IO workload.
> 
> I can't see any read lock requests.
> 
> So why the change?

Hi David,

You can check the context of this patch in below link:

https://lore.kernel.org/linux-f2fs-devel/8e094021b958f9fe01df1183a2677882@codeaurora.org/T/#t

BTW, the root cause here is that mutex lock won't serialize callers, so there
could be potential starvation problem when this lock is always grabbed by high
priority tasks.

Thanks,