linux-kernel - Re: [Resend PATCHv2] mm: skip CMA pages when they are not available

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Message-Id: <20230519145839.3b5193e6accf3b13fd619a07@linux-foundation.org>
Date:   Fri, 19 May 2023 14:58:39 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     "zhaoyang.huang" <zhaoyang.huang@...soc.com>,
        Matthew Wilcox <willy@...radead.org>,
        Minchan Kim <minchan@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, ke.wang@...soc.com
Subject: Re: [Resend PATCHv2] mm: skip CMA pages when they are not available

On Fri, 19 May 2023 16:41:41 +0800 Zhaoyang Huang <huangzhaoyang@...il.com> wrote:

> any comments?

Have any of the regular CMA developers commented on a version of this?


I have a couple of little complaints:

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index bd6637f..19fb445 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2225,10 +2225,16 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan,
>         unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
>         unsigned long skipped = 0;
>         unsigned long scan, total_scan, nr_pages;
> +       bool cma_cap = true;
> +       struct page *page;
>         LIST_HEAD(folios_skipped);
>
>         total_scan = 0;
>         scan = 0;
> +       if ((IS_ENABLED(CONFIG_CMA)) && !current_is_kswapd()
> +               && (gfp_migratetype(sc->gfp_mask) != MIGRATE_MOVABLE))
> +               cma_cap = false;
> +

A code comment above this alteration would be good.  Tell the reader
why we're doing this.


>         while (scan < nr_to_scan && !list_empty(src)) {
>                 struct list_head *move_to = src;
>                 struct folio *folio;
> @@ -2239,12 +2245,17 @@ 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) {
> +               page = &folio->page;
> +
> +               if ((folio_zonenum(folio) > sc->reclaim_idx)
> +#ifdef CONFIG_CMA
> +                       || (get_pageblock_migratetype(page) == MIGRATE_CMA && !cma_cap)
> +#endif
> +               ) {
>                         nr_skipped[folio_zonenum(folio)] += nr_pages;
>                         move_to = &folios_skipped;
>                         goto move;
>                 }

That's pretty ugly.  Can we use IS_ENABLED(CONFIG_CMA) here to avoid
the ifdef?