Re: [PATCH V8 1/2] mm: memcg softlimit reclaim rework

[Michal Hocko <mhocko@suse.cz>]

On Thu 02-08-12 14:24:18, Ying Han wrote:
[...]
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 3e0d0cd..88487b3 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1866,7 +1866,22 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
>  	do {
>  		struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
>  
> -		shrink_lruvec(lruvec, sc);
> +		/*
> +		 * Reclaim from mem_cgroup if any of these conditions are met:
> +		 * - this is a targetted reclaim ( not global reclaim)
> +		 * - reclaim priority is less than DEF_PRIORITY
> +		 * - mem_cgroup or its ancestor ( not including root cgroup)
> +		 * exceeds its soft limit
> +		 *
> +		 * Note: The priority check is a balance of how hard to
> +		 * preserve the pages under softlimit. If the memcgs of the
> +		 * zone having trouble to reclaim pages above their softlimit,
> +		 * we have to reclaim under softlimit instead of burning more
> +		 * cpu cycles.
> +		 */
> +		if (!global_reclaim(sc) || sc->priority < DEF_PRIORITY ||
> +				mem_cgroup_over_soft_limit(memcg))
> +			shrink_lruvec(lruvec, sc);
>  
>  		/*
>  		 * Limit reclaim has historically picked one memcg and

I am thinking that we could add a constant for the priority
limit. Something like
#define MEMCG_LOW_SOFTLIMIT_PRIORITY	DEF_PRIORITY

Although it doesn't seem necessary at the moment, because there is just
one location where it matters but it could help in the future.
What do you think?
-- 
Michal Hocko
SUSE Labs

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