On Sat, 24 May 2025 09:59:53 +0800 Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
> On some large machines with a high number of CPUs running a 64K pagesize
> kernel, 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.
>
> Fixes: f1a7941243c1 ("mm: convert mm's rss stats into percpu_counter")
Three years ago.
> Tested-by Donet Tom <donettom@xxxxxxxxxxxxx>
> Reviewed-by: Aboorva Devarajan <aboorvad@xxxxxxxxxxxxx>
> Tested-by: Aboorva Devarajan <aboorvad@xxxxxxxxxxxxx>
> Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
> Acked-by: SeongJae Park <sj@xxxxxxxxxx>
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Thanks, I added cc:stable to this.
