linux-kernel - Re: [PATCH v3] writeback: factor out balance_wb

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Date: Thu, 13 Jun 2024 16:51:20 +0800
From: Kemeng Shi <shikemeng@...weicloud.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: willy@...radead.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] writeback: factor out balance_wb_limits to remove
 repeated code



on 6/12/2024 5:52 AM, Andrew Morton wrote:
> On Thu,  6 Jun 2024 11:35:47 +0800 Kemeng Shi <shikemeng@...weicloud.com> wrote:
> 
>> Factor out balance_wb_limits to remove repeated code
>>
>> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
>> ---
>>  mm/page-writeback.c | 25 +++++++++++++++++--------
>>  1 file changed, 17 insertions(+), 8 deletions(-)
>>
>> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
>> index bf050abd9053..f611272d3c5b 100644
>> --- a/mm/page-writeback.c
>> +++ b/mm/page-writeback.c
>> @@ -1783,6 +1783,21 @@ static inline void wb_dirty_exceeded(struct dirty_throttle_control *dtc,
>>  		((dtc->dirty > dtc->thresh) || strictlimit);
>>  }
>>  
>> +/*
>> + * The limits fileds dirty_exceeded and pos_ratio won't be updated if wb is
>> + * in freerun state. Please don't use these invalid fileds in freerun case.
> 
> s/fileds/fields/.  I queued a fix for this.
Thanks for fixing this.
> 
>> + */
>> +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);
>> +}
>> +
>>  /*
>>   * balance_dirty_pages() must be called by processes which are generating dirty
>>   * data.  It looks at the number of dirty pages in the machine and will force
>> @@ -1869,12 +1884,9 @@ 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;
> 
> Would it be neater to do
> 
> 		if (balance_wb_limits(...))
> 			goto free_running;
> 
> ?
Here are two reasons why I retrieve freerun info from dtc:
1. Retrieve freerun and other calculated info from balance_domain_limits and
balance_wb_limits in the same way. Personly think it's cleaner.
2. It's more clear that we stop to limit pages because of freerun state of
wb.
> 
> That would require a balance_wb_limits() comment update and probably
> name change.  Just a thought.
> 
>