Re: [PATCHv4] mm: skip CMA pages when they are not available

[Matthew Wilcox <willy@infradead.org>]

On Mon, May 22, 2023 at 02:36:03PM +0800, zhaoyang.huang wrote:
> +#ifdef CONFIG_CMA
> +/*
> + * It is waste of effort to scan and reclaim CMA pages if it is not available
> + * for current allocation context
> + */
> +static bool skip_cma(struct folio *folio, struct scan_control *sc)
> +{
> +	if (!current_is_kswapd() &&
> +			gfp_migratetype(sc->gfp_mask) != MIGRATE_MOVABLE &&
> +			get_pageblock_migratetype(&folio->page) == MIGRATE_CMA)
> +		return true;
> +	return false;
> +}
> +#else
> +static bool skip_cma(struct folio *folio, struct scan_control *sc)
> +{
> +	return false;
> +}
> +#endif
> +
>  /*
>   * Isolating page from the lruvec to fill in @dst list by nr_to_scan times.
>   *
> @@ -2239,7 +2259,8 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan,
>  		nr_pages = folio_nr_pages(folio);
>  		total_scan += nr_pages;
>  
> -		if (folio_zonenum(folio) > sc->reclaim_idx) {
> +		if (folio_zonenum(folio) > sc->reclaim_idx ||
> +				skip_cma(folio, sc)) {
>  			nr_skipped[folio_zonenum(folio)] += nr_pages;
>  			move_to = &folios_skipped;
>  			goto move;

I have no idea if what this patch is trying to accomplish is correct,
but I no longer object to how it is doing it.