linux-kernel - Re: [mm] 2d146aa3aa: vm-scalability.throughput -36.4% regression

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Date:   Tue, 31 Aug 2021 11:23:04 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        andi.kleen@...el.com, kernel test robot <oliver.sang@...el.com>,
        Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...e.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Balbir Singh <bsingharora@...il.com>,
        Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        kernel test robot <lkp@...el.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        Zhengjun Xing <zhengjun.xing@...ux.intel.com>
Subject: Re: [mm] 2d146aa3aa: vm-scalability.throughput -36.4% regression

On Tue, Aug 31, 2021 at 02:30:36PM +0800, Feng Tang <feng.tang@...el.com> wrote:
> Yes, I tried many re-arrangement of the members of cgroup_subsys_state,
> and even close members of memcg, but there were no obvious changes.
> What can recover the regresion is adding 128 bytes padding in the css,
> no matter at the start, end or in the middle.

Do you mean the padding added outside the .cgroup--.refcnt members area
also restores the benchmark results? (Or you refer to paddings that move
.cgroup and .refcnt across a cacheline border ?) I'm asking to be sure
we have correct understanding of what members are contended (what's the
frequent writer).

Thanks,
Michal