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

[Chen Ridong]

On 2025/4/28 11:43, Kairui Song wrote:
> On Fri, Apr 18, 2025 at 5:45 AM Roman Gushchin <roman.gushchin@xxxxxxxxx> 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