Received-SPF: pass (google.com: domain of linux-kernel+bounces-198663-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Subject: Re: [PATCH v2 8/8] writeback: factor out balance_wb_limits to remove
 repeated code
To: Tejun Heo <tj@kernel.org>
Cc: willy@infradead.org, akpm@linux-foundation.org,
 linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
 linux-kernel@vger.kernel.org
References: <20240514125254.142203-1-shikemeng@huaweicloud.com>
 <20240514125254.142203-9-shikemeng@huaweicloud.com>
 <ZljGiunxmVAlW6EE@slm.duckdns.org>
From: Kemeng Shi <shikemeng@huaweicloud.com>
Message-ID: <cfbbcc80-7db1-8277-98ab-1f32c3a629ab@huaweicloud.com>
Date: Mon, 3 Jun 2024 14:39:18 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
 Thunderbird/60.5.0
Precedence: bulk
MIME-Version: 1.0
In-Reply-To: <ZljGiunxmVAlW6EE@slm.duckdns.org>
Content-Type: text/plain; charset=gbk
Content-Transfer-Encoding: 7bit


Hello,
on 5/31/2024 2:33 AM, Tejun Heo wrote:
> Hello,
> 
> On Tue, May 14, 2024 at 08:52:54PM +0800, Kemeng Shi wrote:
>> +static void balance_wb_limits(struct dirty_throttle_control *dtc,
>> +			      bool strictlimit)
>> +{
>> +	wb_dirty_freerun(dtc, strictlimit);
>> +	if (dtc->freerun)
>> +		return;
>> +
>> +	wb_dirty_exceeded(dtc, strictlimit);
>> +	wb_position_ratio(dtc);
>> +}
> ...
>> @@ -1869,12 +1880,9 @@ static int balance_dirty_pages(struct bdi_writeback *wb,
>>  		 * Calculate global domain's pos_ratio and select the
>>  		 * global dtc by default.
>>  		 */
>> -		wb_dirty_freerun(gdtc, strictlimit);
>> +		balance_wb_limits(gdtc, strictlimit);
>>  		if (gdtc->freerun)
>>  			goto free_running;
>> -
>> -		wb_dirty_exceeded(gdtc, strictlimit);
>> -		wb_position_ratio(gdtc);
>>  		sdtc = gdtc;
> 
> Isn't this a bit nasty? The helper skips updating states because it knows
> the caller is not going to use them? I'm not sure the slight code reduction
> justifies the added subtlety.

It's a general rule that wb should not be limited if the wb is in freerun state.
So I think it's intuitive to obey the rule in both balance_wb_limits and it's
caller in which case balance_wb_limits and it's caller should stop to do anything
when freerun state of wb is first seen.
But no insistant on this...

Thanks.
> 
> Thanks.
>