linux-kernel - Re: [PATCH 4/8] mm/vmscan: save a bit of stack space in shrink

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Date:   Wed, 30 Mar 2022 09:59:51 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/8] mm/vmscan: save a bit of stack space in shrink_lruvec

On 2022/3/29 22:00, Christoph Hellwig wrote:
> On Tue, Mar 29, 2022 at 09:26:15PM +0800, Miaohe Lin wrote:
>> LRU_UNEVICTABLE is not taken into account when shrink lruvec. So we can
>> save a bit of stack space by shrinking the array size of nr and targets
>> to NR_LRU_LISTS - 1. No functional change intended.
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>> ---
>>  mm/vmscan.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index a6e60c78d058..ebd8ffb63673 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -2862,8 +2862,9 @@ static bool can_age_anon_pages(struct pglist_data *pgdat,
>>  
>>  static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
>>  {
>> -	unsigned long nr[NR_LRU_LISTS];
>> -	unsigned long targets[NR_LRU_LISTS];
>> +	/* LRU_UNEVICTABLE is not taken into account. */
>> +	unsigned long nr[NR_LRU_LISTS - 1];
>> +	unsigned long targets[NR_LRU_LISTS - 1];
> 
> This looks like a problem waiting to happen..

IIUC, I am changing the array size to what it exactly uses now. And LRU_UNEVICTABLE won't be
used anyway. Could you please tell me what kind of problem is waiting to happen ? If this
will result in actual risk, I will drop this patch.

Thanks.

> 
> .
>