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

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Date:   Mon, 27 Nov 2023 17:58:24 -0800
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Oliver Sang <oliver.sang@...el.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
Subject: Re: [PATCH v3 3/5] mm: memcg: make stats flushing threshold per-memcg

On Mon, Nov 27, 2023 at 5:46 PM Oliver Sang <oliver.sang@...el.com> wrote:
>
> 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?

I think it would be useful to know if there are
regressions/improvements in other microbenchmarks, at least to
investigate whether they represent real regressions.