Re: [PATCH 1/9] mm, page_alloc: clean up pageset high and batch update

[Michal Hocko]

On Tue 22-09-20 16:37:04, Vlastimil Babka wrote:
> The updates to pcplists' high and batch valued 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@xxxxxxx>
> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>

yes this looks better, the original code was really hard to follow.

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  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 60a0e94645a6..a163c5e561f2 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5823,7 +5823,7 @@ 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);
>  
> @@ -5891,7 +5891,7 @@ 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();
> @@ -6200,12 +6200,6 @@ 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;
> @@ -6218,35 +6212,32 @@ 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)
> -- 
> 2.28.0

-- 
Michal Hocko
SUSE Labs