earlyoom service: Cannot configure second part of -m/-s parameters

[nh2]

Issue description

The earlyoom module requires type = int:

nixpkgs/nixos/modules/services/system/earlyoom.nix

Lines 20 to 29 in 7401afc

	freeMemThreshold = mkOption {
	type = types.int;
	default = 10;
	description = ''
	Minimum of availabe memory (in percent).
	If the free memory falls below this threshold and the analog is true for
	<option>services.earlyoom.freeSwapThreshold</option>
	the killing begins.
	'';
	};

but in fact it can be given docs

  -m PERCENT[,KILL_PERCENT] set available memory minimum to PERCENT of total
                            (default 10 %).
                            earlyoom sends SIGTERM once below PERCENT, then
                            SIGKILL once below KILL_PERCENT (default PERCENT/2).
  -s PERCENT[,KILL_PERCENT] set free swap minimum to PERCENT of total (default
                            10 %).
                            Note: both memory and swap must be below minimum for
                            earlyoom to act.

so e.g. -m 10,5 to configure KILL_PERCENT.

That means the KILL_PERCENT setting is currently not configurable in NixOS.

It is very important to configure it, because as written:

both memory and swap must be below minimum for earlyoom to act.

That means earlyoom will only start terminating processes after a large amount of swap is full, which can take forever to happen, thus defeating a major point of earlyoom. (You can work around that by completely disabling swap, but then you can't suspend-to-disk either.)

Even if you set freeSwapThreshold = 100, that will translate to to -s 100,50 by default, so that's 50% of swap filled!

This is why we need to allow the user to configure KILL_PERCENT, so that they can set it to an impactful value like -s 100,100.

We will have to change away from type = int, probably to accept both int and string for backwards compatibility.

Steps to reproduce

Set up earlyoom with swap, run out of memory, see your system freeze.

Technical details

19.09 (same for current master).

---

CC @wedens @ljli as past contributors.

[ljli]

It seems they changed the behavior of the flag: rfjakob/earlyoom@bcd1ad4.
Previously it only accepted one value and always SIGKILL'd, now it still uses the limit in case one value is passed but tries SIGTERM instead of SIGKILL.
Personally I would like freeMemThreshold and freeSwapThreshold to be used in both tuple components to restore the original behavior.
The new flag behavior could be covered with new options freeMemThreshold{SigKill,SigTerm} respective freeSwapThreshold{SigKill,SigTerm} that would be mutually exclusive with freeMemThreshold respective freeSwapThreshold.
On the other hand the changed behavior was introduced some time ago in e5508a4, so theoretical someone could rely on the new behavior.

[nh2]

@ljli I also liked the old behaviour much better, but I think it would be extra confusing to deviate from upstream's defaults.

Would you be up to implementing

The new flag behavior could be covered with new options freeMemThreshold{SigKill,SigTerm} respective freeSwapThreshold{SigKill,SigTerm} that would be mutually exclusive with freeMemThreshold respective freeSwapThreshold.

? And then we would add extra documentation to highlight

both memory and swap must be below minimum for earlyoom to act.

and point out what you have to set to get the old behaviour back.

[stale]

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[nh2]

Still relevant

[stale]

I marked this as stale due to inactivity. → More info