netdev - Re: [PATCH v2 3/3] memcg: increase MEMCG_CHARGE

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Date:   Thu, 25 Aug 2022 08:49:05 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <songmuchun@...edance.com>,
        Michal Koutný <mkoutny@...e.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Feng Tang <feng.tang@...el.com>,
        Oliver Sang <oliver.sang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>, lkp@...ts.01.org,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] memcg: increase MEMCG_CHARGE_BATCH to 64

On Thu 25-08-22 00:05:06, Shakeel Butt wrote:
> For several years, MEMCG_CHARGE_BATCH was kept at 32 but with bigger
> machines and the network intensive workloads requiring througput in
> Gbps, 32 is too small and makes the memcg charging path a bottleneck.
> For now, increase it to 64 for easy acceptance to 6.0. We will need to
> revisit this in future for ever increasing demand of higher performance.
> 
> Please note that the memcg charge path drain the per-cpu memcg charge
> stock, so there should not be any oom behavior change. Though it does
> have impact on rstat flushing and high limit reclaim backoff.
> 
> To evaluate the impact of this optimization, on a 72 CPUs machine, we
> ran the following workload in a three level of cgroup hierarchy.
> 
>  $ netserver -6
>  # 36 instances of netperf with following params
>  $ netperf -6 -H ::1 -l 60 -t TCP_SENDFILE -- -m 10K
> 
> Results (average throughput of netperf):
> Without (6.0-rc1)       10482.7 Mbps
> With patch              17064.7 Mbps (62.7% improvement)
> 
> With the patch, the throughput improved by 62.7%.
> 
> Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
> Reported-by: kernel test robot <oliver.sang@...el.com>
> Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> Reviewed-by: Feng Tang <feng.tang@...el.com>
> Acked-by: Roman Gushchin <roman.gushchin@...ux.dev>

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

> ---
> Changes since v1:
> - Updated commit message
> 
>  include/linux/memcontrol.h | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 4d31ce55b1c0..70ae91188e16 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -354,10 +354,11 @@ struct mem_cgroup {
>  };
>  
>  /*
> - * size of first charge trial. "32" comes from vmscan.c's magic value.
> - * TODO: maybe necessary to use big numbers in big irons.
> + * size of first charge trial.
> + * TODO: maybe necessary to use big numbers in big irons or dynamic based of the
> + * workload.
>   */
> -#define MEMCG_CHARGE_BATCH 32U
> +#define MEMCG_CHARGE_BATCH 64U
>  
>  extern struct mem_cgroup *root_mem_cgroup;
>  
> -- 
> 2.37.1.595.g718a3a8f04-goog

-- 
Michal Hocko
SUSE Labs