linux-kernel - Re: [PATCH v3 3/7] mm, page_alloc: remove setup

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Date:   Wed, 11 Nov 2020 11:23:48 +0100
From:   Pankaj Gupta <pankaj.gupta.linux@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v3 3/7] mm, page_alloc: remove setup_pageset()

> We initialize boot-time pagesets with setup_pageset(), which sets high and
> batch values that effectively disable pcplists.
>
> We can remove this wrapper if we just set these values for all pagesets in
> pageset_init(). Non-boot pagesets then subsequently update them to the proper
> values.
>
> No functional change.
>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> Reviewed-by: David Hildenbrand <david@...hat.com>
> Reviewed-by: Oscar Salvador <osalvador@...e.de>
> Acked-by: Michal Hocko <mhocko@...e.com>
> ---
>  mm/page_alloc.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2fa432762908..5a8ec7d94884 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5911,7 +5911,7 @@ static void build_zonelists(pg_data_t *pgdat)
>   * not check if the processor is online before following the pageset pointer.
>   * Other parts of the kernel may not check if the zone is available.
>   */
> -static void setup_pageset(struct per_cpu_pageset *p);
> +static void pageset_init(struct per_cpu_pageset *p);
>  static DEFINE_PER_CPU(struct per_cpu_pageset, boot_pageset);
>  static DEFINE_PER_CPU(struct per_cpu_nodestat, boot_nodestats);
>
> @@ -5979,7 +5979,7 @@ build_all_zonelists_init(void)
>          * (a chicken-egg dilemma).
>          */
>         for_each_possible_cpu(cpu)
> -               setup_pageset(&per_cpu(boot_pageset, cpu));
> +               pageset_init(&per_cpu(boot_pageset, cpu));
>
>         mminit_verify_zonelist();
>         cpuset_init_current_mems_allowed();
> @@ -6298,12 +6298,15 @@ static void pageset_init(struct per_cpu_pageset *p)
>         pcp = &p->pcp;
>         for (migratetype = 0; migratetype < MIGRATE_PCPTYPES; migratetype++)
>                 INIT_LIST_HEAD(&pcp->lists[migratetype]);
> -}
>
> -static void setup_pageset(struct per_cpu_pageset *p)
> -{
> -       pageset_init(p);
> -       pageset_update(&p->pcp, 0, 1);
> +       /*
> +        * Set batch and high values safe for a boot pageset. A true percpu
> +        * pageset's initialization will update them subsequently. Here we don't
> +        * need to be as careful as pageset_update() as nobody can access the
> +        * pageset yet.
> +        */
> +       pcp->high = 0;
> +       pcp->batch = 1;
>  }

 Acked-by: Pankaj Gupta <pankaj.gupta@...ud.ionos.com>