linux-kernel - Re: [PATCH RFC 00/28] Eliminate Dying Memory Cgroup

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Message-ID: <38e443b1-582c-44ea-a7d4-6d2135414521@huaweicloud.com>
Date: Sat, 28 Jun 2025 17:21:55 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>, Kairui Song <ryncsn@...il.com>
Cc: Roman Gushchin <roman.gushchin@...ux.dev>,
 Muchun Song <muchun.song@...ux.dev>, Muchun Song <songmuchun@...edance.com>,
 hannes@...xchg.org, mhocko@...nel.org, akpm@...ux-foundation.org,
 david@...morbit.com, zhengqi.arch@...edance.com, yosry.ahmed@...ux.dev,
 nphamcs@...il.com, chengming.zhou@...ux.dev, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org, linux-mm@...ck.org,
 hamzamahfooz@...ux.microsoft.com, apais@...ux.microsoft.com,
 yuzhao@...gle.com
Subject: Re: [PATCH RFC 00/28] Eliminate Dying Memory Cgroup



On 2025/6/28 3:14, Shakeel Butt wrote:
> On Sat, Jun 28, 2025 at 02:54:10AM +0800, Kairui Song wrote:
>> On Fri, Jun 27, 2025 at 5:02 PM Chen Ridong <chenridong@...weicloud.com> wrote:
>>> On 2025/4/28 11:43, Kairui Song wrote:
>>>> On Fri, Apr 18, 2025 at 5:45 AM Roman Gushchin <roman.gushchin@...ux.dev> wrote:
>>>>>
>>>>> On Fri, Apr 18, 2025 at 02:22:12AM +0800, Kairui Song wrote:
>>>>>>
>>>>>> We currently have some workloads running with `nokmem` due to objcg
>>>>>> performance issues. I know there are efforts to improve them, but so
>>>>>> far it's still not painless to have. So I'm a bit worried about
>>>>>> this...
>>>>>
>>>>> Do you mind sharing more details here?
>>>>>
>>>>> Thanks!
>>>>
>>>> Hi,
>>>>
>>>> Sorry for the late response, I was busy with another series and other works.
>>>>
>>>> It's not hard to observe such slow down, for example a simple redis
>>>> test can expose it:
>>>>
>>>> Without nokmem:
>>>> redis-benchmark -h 127.0.0.1 -q -t set,get -n 80000 -c 1
>>>> SET: 16393.44 requests per second, p50=0.055 msec
>>>> GET: 16956.34 requests per second, p50=0.055 msec
>>>>
>>>> With nokmem:
>>>> redis-benchmark -h 127.0.0.1 -q -t set,get -n 80000 -c 1
>>>> SET: 17263.70 requests per second, p50=0.055 msec
>>>> GET: 17410.23 requests per second, p50=0.055 msec
>>>>
>>>> And I'm testing with latest kernel:
>>>> uname -a
>>>> Linux localhost 6.15.0-rc2+ #1594 SMP PREEMPT_DYNAMIC Sun Apr 27
>>>> 15:13:27 CST 2025 x86_64 GNU/Linux
>>>>
>>>> This is just an example. For redis, it can be a workaround by using
>>>> things like redis pipeline, but not all workloads can be adjusted
>>>> that flexibly.
>>>>
>>>> And the slowdown could be amplified in some cases.
>>>
>>> Hi Kairui,
>>>
>>> We've also encountered this issue in our Redis scenario. May I confirm
>>> whether your testing is based on cgroup v1 or v2?
>>>
>>> In our environment using cgroup v1, we've identified memcg_account_kmem
>>> as the critical performance bottleneck function - which, as you know, is
>>> specific to the v1 implementation.
>>>
>>> Best regards,
>>> Ridong
>>
>> Hi Ridong
>>
>> I can confirm I was testing using Cgroup V2, and I can still reproduce
>> it, it seems the performance gap is smaller with the latest upstream
>> though, but still easily observable.
>>
>> My previous observation is that the performance drain behaves
>> differently with different CPUs, my current test machine is an Intel
>> 8255C. I'll do a more detailed performance analysis of this when I
>> have time to work on this. Thanks for the tips!
> 
> Please try with the latest upstream kernel i.e. 6.16 as the charging
> code has changed a lot.

Thanks, I will try.