Re: [PATCH mm-new v3] mm/memcontrol: Add memory.stat_refresh for on-demand stats flushing

[Leon Huang Fu <leon.huangfu@shopee.com>]

On Tue, Nov 11, 2025 at 9:00 AM Chen Ridong <chenridong@huaweicloud.com> wrote:
>
>
>
> On 2025/11/10 21:50, Michal Koutný wrote:
>> Hello Leon.

Hi Ridong,

>>
>> On Mon, Nov 10, 2025 at 06:19:48PM +0800, Leon Huang Fu <leon.huangfu@shopee.com> wrote:
>>> Memory cgroup statistics are updated asynchronously with periodic
>>> flushing to reduce overhead. The current implementation uses a flush
>>> threshold calculated as MEMCG_CHARGE_BATCH * num_online_cpus() for
>>> determining when to aggregate per-CPU memory cgroup statistics. On
>>> systems with high core counts, this threshold can become very large
>>> (e.g., 64 * 256 = 16,384 on a 256-core system), leading to stale
>>> statistics when userspace reads memory.stat files.
>>>
>
> We have encountered this problem multiple times when running LTP tests. It can easily occur when
> using a 64K page size.
>
> error:
>         memcg_stat_rss 10 TFAIL: rss is 0, 266240 expected
>

Have you encountered this problem in real world?

>>> This is particularly problematic for monitoring and management tools
>>> that rely on reasonably fresh statistics, as they may observe data
>>> that is thousands of updates out of date.
>>>
>>> Introduce a new write-only file, memory.stat_refresh, that allows
>>> userspace to explicitly trigger an immediate flush of memory statistics.
>>
[...]
>>
>> Next, v1 and v2 haven't been consistent since introduction of v2 (unlike
>> some other controllers that share code or even cftypes between v1 and
>> v2). So I'd avoid introducing a new file to V1 API.
>>
>
> We encountered this problem in v1, I think this is a common problem should be fixed.

Thanks for pointing that out.

Thanks,
Leon

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