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mapuo/debian_ksm.md

Last active Nov 27, 2020
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Enable KSM (Kernel Same-Page Merging) on boot in Debian

Enable KSM (Kernel Same-Page Merging) on boot in Debian

I have installed and run Netdata on my Debian based home server and I wanted to enable KSM after Netdata installer suggested it could save some RAM.

To enable the KSM on boot in Debian you I executed these steps:

  1. Install ksmtuned without all the QEMU dependencies:
sudo apt-get install ksmtuned --no-install-recommends
  1. I actually don't need the ksmtuned.service and I did disabled it:
sudo systemctl stop ksmtuned.service
sudo systemctl disable ksmtuned.service
  1. Finally if:
sudo cat /sys/kernel/mm/ksm/run

returns 0 restart the ksm.service:

sudo systemctl restart ksm.service
@andyforceno

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@andyforceno andyforceno commented Jun 20, 2020

How does it start on boot without the service? Anyway, even using this, with the service enabled, the setting doesn't seem to persist across reboots for me, on either of my Ubuntu (should work the same as Debian) devices. Probably unique to my systems, but I've yet to figure out the issue.

@mapuo

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@mapuo mapuo commented Jun 24, 2020

The service that does the work is ksm.service and it should be enabled by default.
If it isn't you can do enable it by running: sudo systemctl enable --now ksm.service.

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@andyforceno andyforceno commented Jun 24, 2020

Thanks. I don't have that service for some reason, despite following your steps and everything appeared to proceed without an issue (though I am running Arch, not Debian). I found that not having the ksm service is not a problem. In case anyone else runs into this and wants a different solution: you can use systemd's temporary files system to enable ksm at boot time (you will need to reboot or echo 1 > /sys/kernel/mm/ksm/run to enable it, though).

Create /etc/tmpfiles.d/ksm.conf with the contents:

w /sys/kernel/mm/ksm/run - - - - 1

Also, you can verify KSM is working by checking /sys/kernel/mm/ksm/pages_shared. If the output of that is a non-zero number, you are good to go.

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