netdev - Re: [PATCH v2 2/3] mm: page_counter: rearrange struct page

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Date:   Wed, 24 Aug 2022 17:33:30 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <songmuchun@...edance.com>,
        =?ISO-8859-1?Q? "Michal_Koutn=FD" ?= <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>, 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 2/3] mm: page_counter: rearrange struct page_counter
 fields

On Thu, 25 Aug 2022 00:05:05 +0000 Shakeel Butt <shakeelb@...gle.com> wrote:

> With memcg v2 enabled, memcg->memory.usage is a very hot member for
> the workloads doing memcg charging on multiple CPUs concurrently.
> Particularly the network intensive workloads. In addition, there is a
> false cache sharing between memory.usage and memory.high on the charge
> path. This patch moves the usage into a separate cacheline and move all
> the read most fields into separate cacheline.
> 
> 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		12413.7 Mbps (18.4% improvement)
> 
> With the patch, the throughput improved by 18.4%.
> 
> One side-effect of this patch is the increase in the size of struct
> mem_cgroup. For example with this patch on 64 bit build, the size of
> struct mem_cgroup increased from 4032 bytes to 4416 bytes. However for
> the performance improvement, this additional size is worth it. In
> addition there are opportunities to reduce the size of struct
> mem_cgroup like deprecation of kmem and tcpmem page counters and
> better packing.

Did you evaluate the effects of using a per-cpu counter of some form?