Re: [PATCH v2] mm: fix the inaccurate memory statistics issue for users

[Vlastimil Babka]

On 6/9/25 10:52 AM, Vlastimil Babka wrote:
> On 6/9/25 10:31 AM, Ritesh Harjani (IBM) wrote:
>> Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:
>>
>>> On 2025/6/9 15:35, Michal Hocko wrote:
>>>> On Mon 09-06-25 10:57:41, Ritesh Harjani wrote:
>>>>>
>>>>> Any reason why we dropped the Fixes tag? I see there were a series of
>>>>> discussion on v1 and it got concluded that the fix was correct, then why
>>>>> drop the fixes tag?
>>>>
>>>> This seems more like an improvement than a bug fix.
>>>
>>> Yes. I don't have a strong opinion on this, but we (Alibaba) will 
>>> backport it manually,
>>>
>>> because some of user-space monitoring tools depend 
>>> on these statistics.
>>
>> That sounds like a regression then, isn't it?
> 
> Hm if counters were accurate before f1a7941243c1 and not afterwards, and
> this is making them accurate again, and some userspace depends on it,
> then Fixes: and stable is probably warranted then. If this was just a
> perf improvement, then not. But AFAIU f1a7941243c1 was the perf
> improvement...

Dang, should have re-read the commit log of f1a7941243c1 first. It seems
like the error margin due to batching existed also before f1a7941243c1.

" This patch converts the rss_stats into percpu_counter to convert the
error  margin from (nr_threads * 64) to approximately (nr_cpus ^ 2)."

so if on some systems this means worse margin than before, the above
"if" chain of thought might still hold.

> 
>> -ritesh
>