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

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Message-ID: <CALvZod6neFJVCs+qwL5CLmaux3iPjRZY6vdvCt-aNsENnObe-w@mail.gmail.com>
Date:   Thu, 28 Apr 2022 06:16:09 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Yin Fengwei <fengwei.yin@...el.com>
Cc:     kernel test robot <oliver.sang@...el.com>,
        Yosry Ahmed <yosryahmed@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        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,
        kernel test robot <lkp@...el.com>,
        Huang Ying <ying.huang@...el.com>,
        Feng Tang <feng.tang@...el.com>,
        Xing Zhengjun <zhengjun.xing@...ux.intel.com>
Subject: Re: [memcg] a8c49af3be: hackbench.throughput -13.7% regression

On Wed, Apr 27, 2022 at 10:12 PM Yin Fengwei <fengwei.yin@...el.com> wrote:
>
> Hi Shakeel,
>
> On 4/27/2022 1:02 PM, Shakeel Butt wrote:
> > Can you to comment out the following block instead of the above line
> > and see if there is any impact?
>
> Changed the code as following:
>
> +static void memcg_account_kmem(struct mem_cgroup *memcg, int nr_pages)
> +{
> +       mod_memcg_state(memcg, MEMCG_KMEM, nr_pages);
> +
> +#if    0
> +       if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
> +               if (nr_pages > 0)
> +                       page_counter_charge(&memcg->kmem, nr_pages);
> +               else
> +                       page_counter_uncharge(&memcg->kmem, -nr_pages);
> +       }
> +#endif
> +}
> +
>
> The hackbench test result is 147% better:
>
> 086f694a75e1a283 cee08cab8eefaaffdec62343e8d
> ---------------- ---------------------------
>        fail:runs  %reproduction    fail:runs
>            |             |             |
>        8691:15      -52942%         750:6     dmesg.timestamp:last
>            :15          13%           2:6     last_state.booting
>            :15          13%           2:6     last_state.is_incomplete_run
>           1:15          -7%            :6     kmsg.common_interrupt:#No_irq_handler_for_vector
>           2:15         -18%            :6     kmsg.timestamp:common_interrupt:#No_irq_handler_for_vector
>        4656:15      -26039%         750:6     kmsg.timestamp:last
>          %stddev     %change         %stddev
>              \          |                \
>     143619 ±  4%    +147.0%     354807 ±  2%  hackbench.throughput   <------
>     475.91 ±  4%     -58.8%     196.09 ±  2%  hackbench.time.elapsed_time
>
>

Thanks for testing. We should spend time to deprecate memcg->kmem page
counter instead of optimizing MEMCG_KMEM.

Actually we can deprecate kmem page_counter usage, limit and failcnt
easily by replacing them with memcg_page_state(MEMCG_KMEM),
PAGE_COUNTER_MAX and 0. The kmem.max_usage_in_bytes would be a bit
tricky.