linux-kernel - Re: [PATCH v3 2/7] mm, page_alloc: calculate pageset high and batch once per zone

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Date:   Wed, 11 Nov 2020 11:19:43 +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 2/7] mm, page_alloc: calculate pageset high and batch
 once per zone

> We currently call pageset_set_high_and_batch() for each possible cpu, which
> repeats the same calculations of high and batch values.
>
> Instead call the function just once per zone, and make it apply the calculated
> values to all per-cpu pagesets of the zone.
>
> This also allows removing the zone_pageset_init() and __zone_pcp_update()
> wrappers.
>
> 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 | 42 ++++++++++++++++++------------------------
>  1 file changed, 18 insertions(+), 24 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3f1c57344e73..2fa432762908 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6307,13 +6307,14 @@ static void setup_pageset(struct per_cpu_pageset *p)
>  }
>
>  /*
> - * Calculate and set new high and batch values for given per-cpu pageset of a
> + * Calculate and set new high and batch values for all per-cpu pagesets of a
>   * zone, based on the zone's size and the percpu_pagelist_fraction sysctl.
>   */
> -static void pageset_set_high_and_batch(struct zone *zone,
> -                                      struct per_cpu_pageset *p)
> +static void zone_set_pageset_high_and_batch(struct zone *zone)
>  {
>         unsigned long new_high, new_batch;
> +       struct per_cpu_pageset *p;
> +       int cpu;
>
>         if (percpu_pagelist_fraction) {
>                 new_high = zone_managed_pages(zone) / percpu_pagelist_fraction;
> @@ -6325,23 +6326,25 @@ static void pageset_set_high_and_batch(struct zone *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)
> -{
> -       struct per_cpu_pageset *pcp = per_cpu_ptr(zone->pageset, cpu);
>
> -       pageset_init(pcp);
> -       pageset_set_high_and_batch(zone, pcp);
> +       for_each_possible_cpu(cpu) {
> +               p = per_cpu_ptr(zone->pageset, cpu);
> +               pageset_update(&p->pcp, new_high, new_batch);
> +       }
>  }
>
>  void __meminit setup_zone_pageset(struct zone *zone)
>  {
> +       struct per_cpu_pageset *p;
>         int cpu;
> +
>         zone->pageset = alloc_percpu(struct per_cpu_pageset);
> -       for_each_possible_cpu(cpu)
> -               zone_pageset_init(zone, cpu);
> +       for_each_possible_cpu(cpu) {
> +               p = per_cpu_ptr(zone->pageset, cpu);
> +               pageset_init(p);
> +       }
> +
> +       zone_set_pageset_high_and_batch(zone);
>  }
>
>  /*
> @@ -8080,15 +8083,6 @@ int lowmem_reserve_ratio_sysctl_handler(struct ctl_table *table, int write,
>         return 0;
>  }
>
> -static void __zone_pcp_update(struct zone *zone)
> -{
> -       unsigned int cpu;
> -
> -       for_each_possible_cpu(cpu)
> -               pageset_set_high_and_batch(zone,
> -                               per_cpu_ptr(zone->pageset, cpu));
> -}
> -
>  /*
>   * percpu_pagelist_fraction - changes the pcp->high for each zone on each
>   * cpu.  It is the fraction of total pages in each zone that a hot per cpu
> @@ -8121,7 +8115,7 @@ int percpu_pagelist_fraction_sysctl_handler(struct ctl_table *table, int write,
>                 goto out;
>
>         for_each_populated_zone(zone)
> -               __zone_pcp_update(zone);
> +               zone_set_pageset_high_and_batch(zone);
>  out:
>         mutex_unlock(&pcp_batch_high_lock);
>         return ret;
> @@ -8746,7 +8740,7 @@ EXPORT_SYMBOL(free_contig_range);
>  void __meminit zone_pcp_update(struct zone *zone)
>  {
>         mutex_lock(&pcp_batch_high_lock);
> -       __zone_pcp_update(zone);
> +       zone_set_pageset_high_and_batch(zone);
>         mutex_unlock(&pcp_batch_high_lock);
>  }

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