On Fri, 23 May 2025 11:16:13 +0800 Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
> On some large machines with a high number of CPUs running a 64K kernel,
What does 64K kernel means?
> we found that the 'RES' field is always 0 displayed by the top command
> for some processes, which will cause a lot of confusion for users.
>
> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> 875525 root 20 0 12480 0 0 R 0.3 0.0 0:00.08 top
> 1 root 20 0 172800 0 0 S 0.0 0.0 0:04.52 systemd
>
> The main reason is that the batch size of the percpu counter is quite large
> on these machines, caching a significant percpu value, since converting mm's
> rss stats into percpu_counter by commit f1a7941243c1 ("mm: convert mm's rss
> stats into percpu_counter"). Intuitively, the batch number should be optimized,
> but on some paths, performance may take precedence over statistical accuracy.
> Therefore, introducing a new interface to add the percpu statistical count
> and display it to users, which can remove the confusion. In addition, this
> change is not expected to be on a performance-critical path, so the modification
> should be acceptable.
>
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Acked-by: SeongJae Park <sj@xxxxxxxxxx>
Thanks,
SJ
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