Preserving the mobility of ZONE

Preserving the mobility of ZONE_MOVABLE

Posted Jan 25, 2021 11:14 UTC (Mon) by amarao (guest, #87073)
In reply to: Preserving the mobility of ZONE_MOVABLE by zlynx
Parent article: Preserving the mobility of ZONE_MOVABLE

Can you elaborate this a bit further, please? What you've done and how you've notice it need to be done?

to post comments

Preserving the mobility of ZONE_MOVABLE

Posted Jan 25, 2021 17:26 UTC (Mon) by zlynx (guest, #2285) [Link]

Sure.

I built this desktop PC with 64 GiB of RAM. I wanted it to have plenty of THP (Transparent Huge Pages) available so I knew I needed to use ZONE_MOVABLE. I use them for Java and KVM virtual machines. And just for fun.

To create the movable zone, you give one of two command-line options to the kernel. You can use "kernelcore" or "movablecore." They are opposites of each other. I started out using "kernelcore=8G" which provides 8 GiB to the "kernel", but really for all non-movable memory needs.

I have a little script for THP settings I run at bootup as well:

> cd /sys/kernel/mm/transparent_hugepage || exit 1
> echo always > enabled
> echo defer+madvise > defrag
> echo within_size > shmem_enabled
> echo 500 > khugepaged/scan_sleep_millisecs
> echo 500 > khugepaged/alloc_sleep_millisecs

I noticed that playing Youtube videos would start to have strange sound gaps and tracked that to PulseAudio not running on schedule. Which is weird because it is set as real-time. I also noticed that games run from Steam would have sound and video hiccups as well.

I use the "atop" monitoring program a lot and I eventually noticed that when sound problems started to happen, the "slab" number in the memory monitoring would exceed 4G. Which was half of the non-movable RAM allocation.

I am still not exactly sure which kernel operation PulseAudio was hitting 10ms of latency on but when I increased kernelcore to 16G the problem disappeared.

Is this what you wanted to know?