linux-kernel - Re: [PATCH v3 1/7] mm, page_alloc: clean up pageset high and batch update

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Date:   Wed, 11 Nov 2020 10:55:04 +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 1/7] mm, page_alloc: clean up pageset high and batch update

> The updates to pcplists' high and batch values are handled by multiple
> functions that make the calculations hard to follow. Consolidate everything
> to pageset_set_high_and_batch() and remove pageset_set_batch() and
> pageset_set_high() wrappers.
>
> The only special case using one of the removed wrappers was:
> build_all_zonelists_init()
>   setup_pageset()
>     pageset_set_batch()
> which was hardcoding batch as 0, so we can just open-code a call to
> pageset_update() with constant parameters instead.
>
> No functional change.
>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> Reviewed-by: Oscar Salvador <osalvador@...e.de>
> Reviewed-by: David Hildenbrand <david@...hat.com>
> Acked-by: Michal Hocko <mhocko@...e.com>
> ---
>  mm/page_alloc.c | 49 ++++++++++++++++++++-----------------------------
>  1 file changed, 20 insertions(+), 29 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7560240fcf7d..3f1c57344e73 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, unsigned long batch);
> +static void setup_pageset(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), 0);
> +               setup_pageset(&per_cpu(boot_pageset, cpu));
>
>         mminit_verify_zonelist();
>         cpuset_init_current_mems_allowed();
> @@ -6288,12 +6288,6 @@ static void pageset_update(struct per_cpu_pages *pcp, unsigned long high,
>         pcp->batch = batch;
>  }
>
> -/* a companion to pageset_set_high() */
> -static void pageset_set_batch(struct per_cpu_pageset *p, unsigned long batch)
> -{
> -       pageset_update(&p->pcp, 6 * batch, max(1UL, 1 * batch));
> -}
> -
>  static void pageset_init(struct per_cpu_pageset *p)
>  {
>         struct per_cpu_pages *pcp;
> @@ -6306,35 +6300,32 @@ static void pageset_init(struct per_cpu_pageset *p)
>                 INIT_LIST_HEAD(&pcp->lists[migratetype]);
>  }
>
> -static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
> +static void setup_pageset(struct per_cpu_pageset *p)
>  {
>         pageset_init(p);
> -       pageset_set_batch(p, batch);
> +       pageset_update(&p->pcp, 0, 1);
>  }
>
>  /*
> - * pageset_set_high() sets the high water mark for hot per_cpu_pagelist
> - * to the value high for the pageset p.
> + * Calculate and set new high and batch values for given per-cpu pageset of a
> + * zone, based on the zone's size and the percpu_pagelist_fraction sysctl.
>   */
> -static void pageset_set_high(struct per_cpu_pageset *p,
> -                               unsigned long high)
> -{
> -       unsigned long batch = max(1UL, high / 4);
> -       if ((high / 4) > (PAGE_SHIFT * 8))
> -               batch = PAGE_SHIFT * 8;
> -
> -       pageset_update(&p->pcp, high, batch);
> -}
> -
>  static void pageset_set_high_and_batch(struct zone *zone,
> -                                      struct per_cpu_pageset *pcp)
> +                                      struct per_cpu_pageset *p)
>  {
> -       if (percpu_pagelist_fraction)
> -               pageset_set_high(pcp,
> -                       (zone_managed_pages(zone) /
> -                               percpu_pagelist_fraction));
> -       else
> -               pageset_set_batch(pcp, zone_batchsize(zone));
> +       unsigned long new_high, new_batch;
> +
> +       if (percpu_pagelist_fraction) {
> +               new_high = zone_managed_pages(zone) / percpu_pagelist_fraction;
> +               new_batch = max(1UL, new_high / 4);
> +               if ((new_high / 4) > (PAGE_SHIFT * 8))
> +                       new_batch = PAGE_SHIFT * 8;
> +       } else {
> +               new_batch = zone_batchsize(zone);
> +               new_high = 6 * new_batch;
> +               new_batch = max(1UL, 1 * new_batch);
> +       }
> +       pageset_update(&p->pcp, new_high, new_batch);
>  }
>
>  static void __meminit zone_pageset_init(struct zone *zone, int cpu)

Looks good to me.
Acked-by: Pankaj Gupta <pankaj.gupta@...ud.ionos.com>