[PATCH v3] writeback: factor out balance_wb_limits to remove repeated code

[PATCH v3] writeback: factor out balance_wb_limits to remove repeated code

[Kemeng Shi]

Factor out balance_wb_limits to remove repeated code

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.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.
+ */
+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;
-
-		wb_dirty_exceeded(gdtc, strictlimit);
-		wb_position_ratio(gdtc);
 		sdtc = gdtc;
 
 		if (mdtc) {
@@ -1884,12 +1896,9 @@ static int balance_dirty_pages(struct bdi_writeback *wb,
 			 * both global and memcg domains.  Choose the one
 			 * w/ lower pos_ratio.
 			 */
-			wb_dirty_freerun(mdtc, strictlimit);
+			balance_wb_limits(mdtc, strictlimit);
 			if (mdtc->freerun)
 				goto free_running;
-
-			wb_dirty_exceeded(mdtc, strictlimit);
-			wb_position_ratio(mdtc);
 			if (mdtc->pos_ratio < gdtc->pos_ratio)
 				sdtc = mdtc;
 		}
-- 
2.30.0

Re: [PATCH v3] writeback: factor out balance_wb_limits to remove repeated code

[Andrew Morton]

On Thu,  6 Jun 2024 11:35:47 +0800 Kemeng Shi <shikemeng@huaweicloud.com> wrote:

> Factor out balance_wb_limits to remove repeated code
> 
> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.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.

> + */
> +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;

?

That would require a balance_wb_limits() comment update and probably
name change.  Just a thought.

Re: [PATCH v3] writeback: factor out balance_wb_limits to remove repeated code

[Kemeng Shi]

on 6/12/2024 5:52 AM, Andrew Morton wrote:
> On Thu,  6 Jun 2024 11:35:47 +0800 Kemeng Shi <shikemeng@huaweicloud.com> wrote:
> 
>> Factor out balance_wb_limits to remove repeated code
>>
>> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.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.
> 
>