linux-kernel - Re: [memcg] a8c49af3be: hackbench.throughput -13.7% regression

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Message-ID: <1971eb3a-d689-8b35-e500-8a60f41765db@intel.com>
Date:   Wed, 27 Apr 2022 12:59:20 +0800
From:   Yin Fengwei <fengwei.yin@...el.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
CC:     kernel test robot <oliver.sang@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        "Johannes Weiner" <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, <lkp@...ts.01.org>,
        <lkp@...el.com>, Ying <ying.huang@...el.com>,
        <feng.tang@...el.com>, <zhengjun.xing@...ux.intel.com>
Subject: Re: [memcg] a8c49af3be: hackbench.throughput -13.7% regression

Hi Yosry,

On 4/27/2022 12:34 PM, Yosry Ahmed wrote:
> I am not sure why this specific callsite causes regression, there are
> many callsites that modify stats similarly (whether through
> mod_memcg_state() directly or through other variants like
> mod_lruvec_state()). Maybe the kmem call path is exercised more
> heavily in this benchmark than other call paths that update stats.
perf data didn't show the function commented out either. No idea how
it impact the hackbench.

> 
> The only seemingly expensive operation in the mod_memcg_state() path
> is the call to cgroup_rstat_updated() (through memcg_rstat_updated()).
> One idea off the top of my head is to batch calls to
> cgroup_rstat_updated(), similar to what 11192d9c124d ("memcg: flush
> stats only if updated") did on the flush side. I am interested to see
> what memcg maintainers think about this problem (and the proposed
> solution).
OK. Let's wait.


Regards
Yin, Fengwei