Re: [PATCH 1/9] mm/compaction: use correct list in move_freelist_{head}/{tail}

[Kemeng Shi]

on 8/6/2023 1:11 AM, Andrew Morton wrote:
> On Sat,  5 Aug 2023 19:07:03 +0800 Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx> wrote:
> 
>> The freepage is chained with buddy_list in freelist head. Use buddy_list
>> instead of lru to correct the list operation.
>>
>> ...
>>
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -1395,8 +1395,8 @@ move_freelist_head(struct list_head *freelist, struct page *freepage)
>>  {
>>  	LIST_HEAD(sublist);
>>  
>> -	if (!list_is_last(freelist, &freepage->lru)) {
>> -		list_cut_before(&sublist, freelist, &freepage->lru);
>> +	if (!list_is_last(freelist, &freepage->buddy_list)) {
>> +		list_cut_before(&sublist, freelist, &freepage->buddy_list);
>>  		list_splice_tail(&sublist, freelist);
>>  	}
>>  }
>> @@ -1412,8 +1412,8 @@ move_freelist_tail(struct list_head *freelist, struct page *freepage)
>>  {
>>  	LIST_HEAD(sublist);
>>  
>> -	if (!list_is_first(freelist, &freepage->lru)) {
>> -		list_cut_position(&sublist, freelist, &freepage->lru);
>> +	if (!list_is_first(freelist, &freepage->buddy_list)) {
>> +		list_cut_position(&sublist, freelist, &freepage->buddy_list);
>>  		list_splice_tail(&sublist, freelist);
>>  	}
>>  }
> 
> This looks like a significant error.  Can we speculate about the
> possible runtime effects?
> 
> 
> It seems no runtime effects for now as lru and buddy_list share
the same memory address in a union.