linux-kernel - Re: [PATCH 1/8] mm: vmscan: simplify lruvec_lru

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Date:   Wed, 23 Oct 2019 15:48:24 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 1/8] mm: vmscan: simplify lruvec_lru_size()

On Tue 22-10-19 10:47:56, Johannes Weiner wrote:
> This function currently takes the node or lruvec size and subtracts
> the zones that are excluded by the classzone index of the
> allocation. It uses four different types of counters to do this.
> 
> Just add up the eligible zones.

The original intention was to optimize this for GFP_KERNEL like
allocations by reducing the number of zones to reduce. But considering
this is not called from hot paths I do agree that a simpler code is more
preferable.
 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/vmscan.c | 21 +++++----------------
>  1 file changed, 5 insertions(+), 16 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 1154b3a2b637..57f533b808f2 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -351,32 +351,21 @@ unsigned long zone_reclaimable_pages(struct zone *zone)
>   */
>  unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone_idx)
>  {
> -	unsigned long lru_size = 0;
> +	unsigned long size = 0;
>  	int zid;
>  
> -	if (!mem_cgroup_disabled()) {
> -		for (zid = 0; zid < MAX_NR_ZONES; zid++)
> -			lru_size += mem_cgroup_get_zone_lru_size(lruvec, lru, zid);
> -	} else
> -		lru_size = node_page_state(lruvec_pgdat(lruvec), NR_LRU_BASE + lru);
> -
> -	for (zid = zone_idx + 1; zid < MAX_NR_ZONES; zid++) {
> +	for (zid = 0; zid <= zone_idx; zid++) {
>  		struct zone *zone = &lruvec_pgdat(lruvec)->node_zones[zid];
> -		unsigned long size;
>  
>  		if (!managed_zone(zone))
>  			continue;
>  
>  		if (!mem_cgroup_disabled())
> -			size = mem_cgroup_get_zone_lru_size(lruvec, lru, zid);
> +			size += mem_cgroup_get_zone_lru_size(lruvec, lru, zid);
>  		else
> -			size = zone_page_state(&lruvec_pgdat(lruvec)->node_zones[zid],
> -				       NR_ZONE_LRU_BASE + lru);
> -		lru_size -= min(size, lru_size);
> +			size += zone_page_state(zone, NR_ZONE_LRU_BASE + lru);
>  	}
> -
> -	return lru_size;
> -
> +	return size;
>  }
>  
>  /*
> -- 
> 2.23.0

-- 
Michal Hocko
SUSE Labs