Re: [PATCH v5 2/3] mm/compaction: add support for >0 order folio memory compaction.

[Zi Yan]

On 15 Feb 2024, at 11:57, Vlastimil Babka wrote:

> On 2/14/24 23:04, Zi Yan wrote:
>> @@ -1849,10 +1857,22 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
>>  static void compaction_free(struct folio *dst, unsigned long data)
>>  {
>>  	struct compact_control *cc = (struct compact_control *)data;
>> +	int order = folio_order(dst);
>> +	struct page *page = &dst->page;
>> +
>> +	if (folio_put_testzero(dst)) {
>> +		free_pages_prepare_fpi_none(page, order);
>> +
>> +		INIT_LIST_HEAD(&dst->lru);
>
> (is this even needed? I think the state of first parameter of list_add() is
> never expected to be in particular state?)

There is a __list_add_valid() performing list corruption checks.
>
>>
>> -	list_add(&dst->lru, &cc->freepages);
>> -	cc->nr_freepages++;
>> -	cc->nr_migratepages += 1 << folio_order(dst);
>> +		list_add(&dst->lru, &cc->freepages[order]);
>> +		cc->nr_freepages += 1 << order;
>> +		cc->nr_migratepages += 1 << order;
>
> Hm actually this increment of nr_migratepages should happen even if we lost
> the free page.

Because compaction_free() indicates the page is not migrated and nr_migratepages
should be increased regardless.

Will fix it. Thanks.

>> +	}
>> +	/*
>> +	 * someone else has referenced the page, we cannot take it back to our
>> +	 * free list.
>> +	 */
>>  }


--
Best Regards,
Yan, Zi

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