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

[Vlastimil Babka <vbabka@suse.cz>]

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?)

>  
> -	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.

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