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Subject: Re: [memcg] 0f12156dff: will-it-scale.per_process_ops -33.6%
 regression
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     kernel test robot <oliver.sang@intel.com>,
        Vasily Averin <vvs@virtuozzo.com>,
        Shakeel Butt <shakeelb@google.com>,
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        Yutian Yang <nglaive@gmail.com>,
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        kernel test robot <lkp@intel.com>,
        "Huang, Ying" <ying.huang@intel.com>,
        Feng Tang <feng.tang@intel.com>,
        Zhengjun Xing <zhengjun.xing@linux.intel.com>
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 <CAHk-=wgrF65BpP6P6_a6+k+C8V+JOBiEx0X-c9idiM87uk32FQ@mail.gmail.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <774dee70-69bd-9f95-d197-4cff83e4e633@kernel.dk>
Date:   Tue, 7 Sep 2021 10:43:46 -0600
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On 9/7/21 10:39 AM, Linus Torvalds wrote:
> On Tue, Sep 7, 2021 at 8:46 AM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> Are we at all worried about these? There's been a number of them
>> reported, basically for all the accounting enablements that have been
>> done in this merge window.
> 
> We are worried about them. I'm considering reverting several of them
> because I think the problems are
> 
>  (a) big
> 
>  (b) nontrivial
> 
> and the patches clearly weren't ready and people weren't aware of this issue.

I think that is prudent. When I first enabled it for io_uring it was a
bit of a shit show in terms of performance degradations, and some work
had to be done before it could get enabled in a sane fashion.

The accounting needs to be more efficient if we're seeing 30-50%
slowdowns simply by enabling it on a kmem cache.

-- 
Jens Axboe