linux-kernel - Re: [RFC 4/5] mm, page_alloc: cache pageset high and batch in struct zone

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Message-ID: <20200910113046.GA5848@linux>
Date:   Thu, 10 Sep 2020 13:30:50 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...nel.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        David Hildenbrand <david@...hat.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [RFC 4/5] mm, page_alloc: cache pageset high and batch in struct
 zone

On Mon, Sep 07, 2020 at 06:36:27PM +0200, Vlastimil Babka wrote:
   */
> -static void setup_pageset(struct per_cpu_pageset *p);
> +static void pageset_init(struct per_cpu_pageset *p);

this belongs to the respective patches

> -static void zone_set_pageset_high_and_batch(struct zone *zone)
> +static void zone_set_pageset_high_and_batch(struct zone *zone, bool force_update)
>  {
>  	unsigned long new_high;
>  	unsigned long new_batch;
> @@ -6256,6 +6256,14 @@ static void zone_set_pageset_high_and_batch(struct zone *zone)
>  		new_batch = max(1UL, 1 * new_batch);
>  	}
>  
> +	if (zone->pageset_high != new_high ||
> +	    zone->pageset_batch != new_batch) {
> +		zone->pageset_high = new_high;
> +		zone->pageset_batch = new_batch;
> +	} else if (!force_update) {
> +		return;
> +	}

I am probably missimg something obvious, so sorry, but why do we need
force_update here?
AFAICS, we only want to call pageset_update() in case zone->pageset_high/batch
and the new computed high/batch differs, so if everything is equal, why do we want
to call it anyways?

-- 
Oscar Salvador
SUSE L3