linux-kernel - Re: [PATCH 2/9] mm, page_alloc: calculate pageset high and batch once per zone

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Message-ID: <20201005125247.GX4555@dhcp22.suse.cz>
Date:   Mon, 5 Oct 2020 14:52:47 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 2/9] mm, page_alloc: calculate pageset high and batch
 once per zone

On Tue 22-09-20 16:37:05, Vlastimil Babka wrote:
> 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>

I like this. One question below
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 a163c5e561f2..26069c8d1b19 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6219,13 +6219,14 @@ 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;
> @@ -6237,23 +6238,25 @@ 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);

I hope I am not misreading the diff but it seems that setup_zone_pageset
is calling pageset_init which is then done again by
zone_set_pageset_high_and_batch as a part of pageset_update

-- 
Michal Hocko
SUSE Labs