linux-kernel - Re: [PATCH 6/6] writeback: remove unneeded GDTC_INIT_NO

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Date: Thu, 21 Mar 2024 15:12:21 +0800
From: Kemeng Shi <shikemeng@...weicloud.com>
To: Tejun Heo <tj@...nel.org>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 willy@...radead.org, bfoster@...hat.com, jack@...e.cz, dsterba@...e.com,
 mjguzik@...il.com, dhowells@...hat.com, peterz@...radead.org
Subject: Re: [PATCH 6/6] writeback: remove unneeded GDTC_INIT_NO_WB



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@...weicloud.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!

> 
> Thanks.
>