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

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Date: Mon, 25 Mar 2024 10:26:20 -1000
From: Tejun Heo <tj@...nel.org>
To: Kemeng Shi <shikemeng@...weicloud.com>
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 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@...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!

Ah, I see. In that case, the proposed change of removing GDTC_INIT_NO_WB
looks good to me.

Thanks.

-- 
tejun