Re: [PATCH 3/5] mm: memcg detect no memcgs above softlimit under zone reclaim.

[Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

(2012/06/07 3:23), Ying Han wrote:
> In memcg kernel, cgroup under its softlimit is not targeted under global
> reclaim. It could be possible that all memcgs are under their softlimit for
> a particular zone. If that is the case, the current implementation will
> burn extra cpu cycles without making forward progress.
> 
> The idea is from LSF discussion where we detect it after the first round of
> scanning and restart the reclaim by not looking at softlimit at all. This
> allows us to make forward progress on shrink_zone().
> 
> Signed-off-by: Ying Han<yinghan@google.com>

Hm, how about adding sc->ignore_softlimit and preserve the result among priority loops ?

Is it better to check 'ignore_softlimit' at every priority updates ?

Thanks,
-Kame

> ---
>   mm/vmscan.c |   18 ++++++++++++++++--
>   1 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 0560783..5d036f5 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2142,6 +2142,10 @@ static void shrink_zone(int priority, struct zone *zone,
>   		.priority = priority,
>   	};
>   	struct mem_cgroup *memcg;
> +	bool over_softlimit, ignore_softlimit = false;
> +
> +restart:
> +	over_softlimit = false;
> 
>   	memcg = mem_cgroup_iter(root, NULL,&reclaim);
>   	do {
> @@ -2163,9 +2167,14 @@ static void shrink_zone(int priority, struct zone *zone,
>   		 * we have to reclaim under softlimit instead of burning more
>   		 * cpu cycles.
>   		 */
> -		if (!global_reclaim(sc) || priority<  DEF_PRIORITY - 2 ||
> -				should_reclaim_mem_cgroup(memcg))
> +		if (ignore_softlimit || !global_reclaim(sc) ||
> +				priority<  DEF_PRIORITY - 2 ||
> +				should_reclaim_mem_cgroup(memcg)) {
>   			shrink_mem_cgroup_zone(priority,&mz, sc);
> +
> +			over_softlimit = true;
> +		}
> +
>   		/*
>   		 * Limit reclaim has historically picked one memcg and
>   		 * scanned it with decreasing priority levels until
> @@ -2182,6 +2191,11 @@ static void shrink_zone(int priority, struct zone *zone,
>   		}
>   		memcg = mem_cgroup_iter(root, memcg,&reclaim);
>   	} while (memcg);
> +
> +	if (!over_softlimit) {
> +		ignore_softlimit = true;
> +		goto restart;
> +	}
>   }
> 
>   /* Returns true if compaction should go ahead for a high-order request */


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