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

Michal Hocko
2020-10-05T13:03:44Z

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@suse.cz>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Reviewed-by: David Hildenbrand <david@redhat.com>

I like this. One question below
Acked-by: Michal Hocko <mhocko@suse.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