Re: [PATCH v3 3/3] mm/page_alloc: Introduce a new sysctl knob vm.pcp_batch_scale_max

[Yafang Shao <laoar.shao@gmail.com>]

On Mon, Aug 5, 2024 at 9:41 AM Huang, Ying <ying.huang@intel.com> wrote:
>
> Yafang Shao <laoar.shao@gmail.com> writes:
>
> [snip]
>
> >
> > Why introduce a systl knob?
> > ===========================
> >
> > From the above data, it's clear that different CPU types have varying
> > allocation latencies concerning zone->lock contention. Typically, people
> > don't release individual kernel packages for each type of x86_64 CPU.
> >
> > Furthermore, for latency-insensitive applications, we can keep the default
> > setting for better throughput.
>
> Do you have any data to prove that the default setting is better for
> throughput?  If so, that will be a strong support for your patch.

No, I don't. The primary reason we can't change the default value from
5 to 0 across our fleet of servers is that you initially set it to 5.
The sysadmins believe you had a strong reason for setting it to 5 by
default; otherwise, it would be considered careless for the upstream
kernel. I also believe you must have had a solid justification for
setting the default value to 5; otherwise, why would you have
submitted your patches?

>
> > In our production environment, we set this
> > value to 0 for applications running on Kubernetes servers while keeping it
> > at the default value of 5 for other applications like big data. It's not
> > common to release individual kernel packages for each application.
> >
>
> [snip]
>
> --
> Best Regards,
> Huang, Ying



--
Regards
Yafang