Re: [PATCH v6 7/7] mm/memcg: use vm_swappiness from target memory cgroup

[Michal Hocko <mhocko@suse.cz>]

On Fri 23-03-12 01:56:43, Konstantin Khlebnikov wrote:
> Use vm_swappiness from memory cgroup which is triggered this memory reclaim.
> This is more reasonable and allows to kill one argument.

Could you be more specific why is this more reasonable? 
I am afraid this might lead to an unexpected behavior when the target
memcg has quite high swappiness while other groups in the hierarchy have
it 0 so we would end up swapping even from those groups.

> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujtisu.com>
> ---
>  mm/vmscan.c |    9 ++++-----
>  1 files changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 9de66be..5e2906d 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1840,12 +1840,11 @@ static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
>  	return shrink_inactive_list(nr_to_scan, mz, sc, priority, lru);
>  }
>  
> -static int vmscan_swappiness(struct mem_cgroup_zone *mz,
> -			     struct scan_control *sc)
> +static int vmscan_swappiness(struct scan_control *sc)
>  {
>  	if (global_reclaim(sc))
>  		return vm_swappiness;
> -	return mem_cgroup_swappiness(mz->mem_cgroup);
> +	return mem_cgroup_swappiness(sc->target_mem_cgroup);
>  }
>  
>  /*
> @@ -1913,8 +1912,8 @@ static void get_scan_count(struct mem_cgroup_zone *mz, struct scan_control *sc,
>  	 * With swappiness at 100, anonymous and file have the same priority.
>  	 * This scanning priority is essentially the inverse of IO cost.
>  	 */
> -	anon_prio = vmscan_swappiness(mz, sc);
> -	file_prio = 200 - vmscan_swappiness(mz, sc);
> +	anon_prio = vmscan_swappiness(sc);
> +	file_prio = 200 - vmscan_swappiness(sc);
>  
>  	/*
>  	 * OK, so we have swap space and a fair amount of page cache
> 
> --
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-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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