Re: [PATCH 6/6] writeback: remove unneeded GDTC_INIT_NO_WB

From: Kemeng Shi <shikemeng@huaweicloud.com>
To: Tejun Heo <tj@kernel.org>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	willy@infradead.org, bfoster@redhat.com, jack@suse.cz,
	dsterba@suse.com, mjguzik@gmail.com, dhowells@redhat.com,
	peterz@infradead.org
Subject: Re: [PATCH 6/6] writeback: remove unneeded GDTC_INIT_NO_WB
Date: Tue, 26 Mar 2024 21:17:37 +0800	[thread overview]
Message-ID: <82ade435-3ad8-7628-4c1d-09399ebdec49@huaweicloud.com> (raw)
In-Reply-To: <ZgHd7GcUslrBEeoi@slm.duckdns.org>


on 3/26/2024 4:26 AM, Tejun Heo wrote:
> On Thu, Mar 21, 2024 at 03:12:21PM +0800, Kemeng Shi wrote:
>>
>>
>> on 3/20/2024 11:15 PM, Tejun Heo wrote:
>>> Hello,
>>>
>>> On Wed, Mar 20, 2024 at 07:02:22PM +0800, Kemeng Shi wrote:
>>>> We never use gdtc->dom set with GDTC_INIT_NO_WB, just remove unneeded
>>>> GDTC_INIT_NO_WB
>>>>
>>>> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
>>> ...
>>>>  void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
>>>>  {
>>>> -	struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
>>>> +	struct dirty_throttle_control gdtc = { };
>>>
>>> Even if it's currently not referenced, wouldn't it still be better to always
>>> guarantee that a dtc's dom is always initialized? I'm not sure what we get
>>> by removing this.
>> As we explicitly use GDTC_INIT_NO_WB to set global_wb_domain before
>> calculating dirty limit with domain_dirty_limits, I intuitively think the dirty
>> limit calculation in domain_dirty_limits is related to global_wb_domain when
>> CONFIG_WRITEBACK_CGROUP is enabled while the truth is not. So this is a little
>> confusing to me.
>> Would it be acceptable to you that we keep useing GDTC_INIT_NO_WB but
>> define GDTC_INIT_NO_WB to null fow now and redefine GDTC_INIT_NO_WB when some
>> member of gdtc is really needed.
>> Of couse I'm not insistent on this. Would like to hear you suggestion. Thanks!
> 
> Ah, I see. In that case, the proposed change of removing GDTC_INIT_NO_WB
> looks good to me.
Sure, will do it in next version. Thanks!
> 
> Thanks.
>