[PATCH] mm/vmscan: simplify the nr assignment logic for pages to scan

[PATCH] mm/vmscan: simplify the nr assignment logic for pages to scan

[Chao Xu]

By default the assignment logic of anonymouns or file inactive
pages and active pages to scan using the same duplicated code
snippet. To simplify the logic, merge the same part.

Signed-off-by: Chao Xu <Chao.Xu9@zeekrlife.com>
---
 mm/vmscan.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 04d8b88e5216..df3c0cbe381f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5932,14 +5932,11 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 		 * scan target and the percentage scanning already complete
 		 */
 		lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
-		nr_scanned = targets[lru] - nr[lru];
-		nr[lru] = targets[lru] * (100 - percentage) / 100;
-		nr[lru] -= min(nr[lru], nr_scanned);
-
-		lru += LRU_ACTIVE;
-		nr_scanned = targets[lru] - nr[lru];
-		nr[lru] = targets[lru] * (100 - percentage) / 100;
-		nr[lru] -= min(nr[lru], nr_scanned);
+		for ( ; lru <= lru + LRU_ACTIVE; lru++) {
+			nr_scanned = targets[lru] - nr[lru];
+			nr[lru] = targets[lru] * (100 - percentage) / 100;
+			nr[lru] -= min(nr[lru], nr_scanned);
+		}
 
 		scan_adjusted = true;
 	}
-- 
2.34.1

Re: [PATCH] mm/vmscan: simplify the nr assignment logic for pages to scan

[Andrew Morton]

On Wed,  9 Nov 2022 15:04:16 +0800 Chao Xu <amos.xuchao@gmail.com> wrote:

> By default the assignment logic of anonymouns or file inactive
> pages and active pages to scan using the same duplicated code
> snippet. To simplify the logic, merge the same part.
> 
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -5932,14 +5932,11 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
>  		 * scan target and the percentage scanning already complete
>  		 */
>  		lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
> -		nr_scanned = targets[lru] - nr[lru];
> -		nr[lru] = targets[lru] * (100 - percentage) / 100;
> -		nr[lru] -= min(nr[lru], nr_scanned);
> -
> -		lru += LRU_ACTIVE;
> -		nr_scanned = targets[lru] - nr[lru];
> -		nr[lru] = targets[lru] * (100 - percentage) / 100;
> -		nr[lru] -= min(nr[lru], nr_scanned);
> +		for ( ; lru <= lru + LRU_ACTIVE; lru++) {

The "lru++" implicitly assumes that LRU_ACTIVE=1.  That happens to be
the case, but a more accurate translation of the existing code would
use "lru += LRU_ACTIVE" here, yes?

> +			nr_scanned = targets[lru] - nr[lru];
> +			nr[lru] = targets[lru] * (100 - percentage) / 100;
> +			nr[lru] -= min(nr[lru], nr_scanned);
> +		}
>  
>  		scan_adjusted = true;
>  	}

Re: [PATCH] mm/vmscan: simplify the nr assignment logic for pages to scan

[Chao Xu]

在 2022/11/10 9:19, Andrew Morton 写道:
> On Wed,  9 Nov 2022 15:04:16 +0800 Chao Xu <amos.xuchao@gmail.com> wrote:
>
>> By default the assignment logic of anonymouns or file inactive
>> pages and active pages to scan using the same duplicated code
>> snippet. To simplify the logic, merge the same part.
>>
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -5932,14 +5932,11 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
>>   		 * scan target and the percentage scanning already complete
>>   		 */
>>   		lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
>> -		nr_scanned = targets[lru] - nr[lru];
>> -		nr[lru] = targets[lru] * (100 - percentage) / 100;
>> -		nr[lru] -= min(nr[lru], nr_scanned);
>> -
>> -		lru += LRU_ACTIVE;
>> -		nr_scanned = targets[lru] - nr[lru];
>> -		nr[lru] = targets[lru] * (100 - percentage) / 100;
>> -		nr[lru] -= min(nr[lru], nr_scanned);
>> +		for ( ; lru <= lru + LRU_ACTIVE; lru++) {
> The "lru++" implicitly assumes that LRU_ACTIVE=1.  That happens to be
> the case, but a more accurate translation of the existing code would
> use "lru += LRU_ACTIVE" here, yes?
By default the value of LRU_ACTIVE is 1，but if someone change it one day, I
use "lru++" maybe facing some exceptions, which is not robust. So I 
agree with
that "lru += LRU_ACTIVE" is appropriate instead of "lru++". I will send 
a new patch.
>> +			nr_scanned = targets[lru] - nr[lru];
>> +			nr[lru] = targets[lru] * (100 - percentage) / 100;
>> +			nr[lru] -= min(nr[lru], nr_scanned);
>> +		}
>>   
>>   		scan_adjusted = true;
>>   	}