linux-kernel - Re: [PATCH v3 3/5] mm: memcg: make stats flushing threshold per-memcg

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Message-ID: <ZWVGS2rNgueGH8uU@xsang-OptiPlex-9020>
Date:   Tue, 28 Nov 2023 09:45:47 +0800
From:   Oliver Sang <oliver.sang@...el.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
CC:     <oe-lkp@...ts.linux.dev>, <lkp@...el.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Domenico Cerasuolo <cerasuolodomenico@...il.com>,
        <cgroups@...r.kernel.org>, <linux-mm@...ck.org>,
        <ying.huang@...el.com>, <feng.tang@...el.com>,
        <fengwei.yin@...el.com>, Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Ivan Babrou <ivan@...udflare.com>, Tejun Heo <tj@...nel.org>,
        Michal Koutný <mkoutny@...e.com>,
        "Waiman Long" <longman@...hat.com>, <kernel-team@...udflare.com>,
        Wei Xu <weixugc@...gle.com>, Greg Thelen <gthelen@...gle.com>,
        <linux-kernel@...r.kernel.org>, <oliver.sang@...el.com>
Subject: Re: [PATCH v3 3/5] mm: memcg: make stats flushing threshold per-memcg

hi, Yosry Ahmed,

On Mon, Nov 27, 2023 at 01:13:44PM -0800, Yosry Ahmed wrote:
> On Wed, Nov 22, 2023 at 5:54 AM kernel test robot <oliver.sang@...el.com> wrote:
> >
> >
> >
> > Hello,
> >
> > kernel test robot noticed a -30.2% regression of will-it-scale.per_thread_ops on:
> >
> >
> > commit: c7fbfc7b4e089c4a9b292b1973a42a5761c1342f ("[PATCH v3 3/5] mm: memcg: make stats flushing threshold per-memcg")
> > url: https://github.com/intel-lab-lkp/linux/commits/Yosry-Ahmed/mm-memcg-change-flush_next_time-to-flush_last_time/20231116-103300
> > base: https://git.kernel.org/cgit/linux/kernel/git/akpm/mm.git mm-everything
> > patch link: https://lore.kernel.org/all/20231116022411.2250072-4-yosryahmed@google.com/
> > patch subject: [PATCH v3 3/5] mm: memcg: make stats flushing threshold per-memcg
> >
> > testcase: will-it-scale
> > test machine: 104 threads 2 sockets (Skylake) with 192G memory
> > parameters:
> >
> >         nr_task: 50%
> >         mode: thread
> >         test: fallocate2
> >         cpufreq_governor: performance
> >
> >
> 
> This regression was also reported in v2, and I explicitly mention it
> in the cover letter here:
> https://lore.kernel.org/lkml/20231116022411.2250072-1-yosryahmed@google.com/

got it. this also reminds us to read cover letter for a patch set in the
future. Thanks!

> 
> In a nutshell, I think this microbenchmark regression does not
> represent real workloads. On the other hand, there are demonstrated
> benefits on real workloads from this series in terms of stats reading
> time.
> 

ok, if there are future versions of this patch, or when it is merged, we will
ignore similar results.

just a small question, since we focus on microbenchmark, if we found other
regression (or improvement) on tests other than will-it-scale::fallocate,
do you want us to send report or just ignore them, either?