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

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Date:   Thu, 10 Nov 2022 10:48:24 +0800
From:   Chao Xu <amos.xuchao@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Chao Xu <Chao.Xu9@...krlife.com>
Subject: Re: [PATCH] mm/vmscan: simplify the nr assignment logic for pages to
 scan


在 2022/11/10 9:19, Andrew Morton 写道:
> On Wed,  9 Nov 2022 15:04:16 +0800 Chao Xu <amos.xuchao@...il.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;
>>   	}