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

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Date:   Thu, 25 May 2023 21:03:29 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     "zhaoyang.huang" <zhaoyang.huang@...soc.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Minchan Kim <minchan@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Zhaoyang Huang <huangzhaoyang@...il.com>, ke.wang@...soc.com
Subject: Re: [PATCHv4] mm: skip CMA pages when they are not available

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.