Add page size system features by RossComputerGuy · Pull Request #12446 · NixOS/nix

RossComputerGuy · 2025-02-11T06:34:17Z

Motivation

Context

Prevents issues like NixOS/nixpkgs#348660 from occurring by adding system features which describe the page size. This has the added benefit of systems with multiple builders of utilizing only compatible page sizes.

Testing this PR involves building this PR and running Nix to build any derivation inside this branch of nixpkgs: https://github.com/RossComputerGuy/nixpkgs/tree/feat/page-size

It should not fail with this error:

error: a 'aarch64-linux' with features {pages-16k, pages-32k, pages-4k, pages-64k, pages-8k} is required to build '/nix/store/njf0b0lzfs9gdyylpdyb8gg6s9x0kq35-bootstrap-stage0-glibc-bootstrapFiles.drv', but I am a 'aarch64-linux' with features {benchmark, big-parallel, gccarch-armv8-a, kvm, nixos-test}

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roberth

This might lead to a mandatoryRejectedSystemFeatures option and machine parameter, or that could be over-engineered.

roberth · 2025-02-15T16:31:55Z


+- [`rejectSystemFeatures`]{#adv-attr-rejectSystemFeatures}\
+
+  If a derivation has the `rejectSystemFeatures` attribute, then Nix will only build it on a machine that does not has the corresponding features set in its [`system-features` configuration](@docroot@/command-ref/conf-file.md#conf-system-features).


Suggested change

If a derivation has the `rejectSystemFeatures` attribute, then Nix will only build it on a machine that does not has the corresponding features set in its [`system-features` configuration](@docroot@/command-ref/conf-file.md#conf-system-features).

If a derivation has the `rejectSystemFeatures` attribute, then Nix will only build it on a machine that does not have the corresponding features set in its [`system-features` configuration](@docroot@/command-ref/conf-file.md#conf-system-features).

Thanks for catching that, it's fixed now.

roberth · 2025-02-15T16:32:10Z

+  rejectSystemFeatures = [ "pages-16k" ];
+  ```
+
+  ensures that the derivation can only be built on a machine which do not have the `pages-16k` feature.


Suggested change

ensures that the derivation can only be built on a machine which do not have the `pages-16k` feature.

ensures that the derivation can only be built on a machine which does not have the `pages-16k` feature.

roberth · 2025-02-15T16:36:45Z

    /* Right platform? */
    if (!parsedDrv->canBuildLocally(worker.store))
-        throw Error("a '%s' with features {%s} is required to build '%s', but I am a '%s' with features {%s}",
+        throw Error("a '%s' with features {%s} & not {%s} is required to build '%s', but I am a '%s' with features {%s}",


Not pretty when empty, but that was already the case for required ones.

Yeah, I'm curious how we should handle things when it's empty.

roberth · 2025-02-15T16:43:34Z

 echo "$output" | grepQuiet builder-build-remote-input-3.sh
 unset output

+# Ensure that input4 was built on store4 due to the required feature.


This isn't obvious from the code below. Could you add assertions that simply check what you're saying here?

I tried getting a test here which would reject builds in the proper way but I'm not confident with the testing framework so I might need guidance.

roberth · 2025-02-19T09:21:16Z

It seems that #12292 introduced a conflict.
@Ericson2314 what is the status of #12410?

Ericson2314

I'm late to this, but I don't think "reject system features" is a good framing of this. I think it's better to keep "positive" rather than "negative reasoning.

For the case of page size, there is set if page sizes which are allowed, and the system is required to have its page sizes be in the set.

RossComputerGuy · 2025-03-18T05:28:58Z

The problem I had with requiredSystemFeatures and the page size was that it applies to all derivations. This would make ranges difficult since then it'll be an & and not || like it should be since the ranges will be different. Reject system features would reject a build when the builder has a specific page size which simplified how this would apply.

A good example of this is if the minimum page size is 16 but a derivation supports the minimum of 4k, the builder would not have the 4k page size feature and would fail saying that it doesn't have the feature.

Ericson2314 · 2025-03-18T18:14:25Z

Yes, it is better to add "or" than "not".

RossComputerGuy · 2025-03-18T18:16:16Z

The problem is how to do an || with system features, the not is much simpler imo.

Ericson2314 · 2025-03-18T18:22:21Z

@RossComputerGuy I don't want to delay this too much, but with structured attrs that gets much easier.

nixos-discourse · 2025-06-04T22:05:21Z

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2025-05-04-nix-team-meeting-minutes-230/65206/1

RossComputerGuy requested a review from Ericson2314 as a code owner February 11, 2025 06:34

RossComputerGuy mentioned this pull request Feb 11, 2025

Add a page size system feature #12426

Open

2 tasks

RossComputerGuy force-pushed the feat/page-size branch from bcb4839 to 0fc68c3 Compare February 11, 2025 07:15

RossComputerGuy marked this pull request as draft February 11, 2025 07:17

github-actions Bot added the with-tests Issues related to testing. PRs with tests have some priority label Feb 14, 2025

RossComputerGuy force-pushed the feat/page-size branch from 1fe2463 to 18057a7 Compare February 14, 2025 20:32

RossComputerGuy marked this pull request as ready for review February 14, 2025 20:40

github-actions Bot added the documentation label Feb 14, 2025

RossComputerGuy requested review from edolstra and fricklerhandwerk as code owners February 14, 2025 20:40

roberth reviewed Feb 15, 2025

View reviewed changes

RossComputerGuy force-pushed the feat/page-size branch from 92050c6 to c4a6266 Compare February 16, 2025 03:11

Add page size system features

6483d40

RossComputerGuy force-pushed the feat/page-size branch 2 times, most recently from 75a730b to 0bcf588 Compare February 19, 2025 14:59

RossComputerGuy added 3 commits February 19, 2025 07:13

Add rejectSystemFeatures to derivations

fb661f2

tests/functional: add reject features test

36c3ae8

Document the reject systems feature

589fe7d

RossComputerGuy force-pushed the feat/page-size branch from 0bcf588 to 589fe7d Compare February 19, 2025 15:13

RossComputerGuy mentioned this pull request Feb 20, 2025

lib.systems: add page size NixOS/nixpkgs#383756

Open

13 tasks

Mic92 added this to Nix team Mar 12, 2025

github-project-automation Bot moved this to To triage in Nix team Mar 12, 2025

Ericson2314 requested changes Mar 18, 2025

View reviewed changes

saghen mentioned this pull request May 13, 2025

nix: fix jemalloc on 16k pages saghen/blink.cmp#1759

Merged

tomberek moved this from To triage to ⚖ To discuss in Nix team Jun 4, 2025


		- [`rejectSystemFeatures`]{#adv-attr-rejectSystemFeatures}\

		If a derivation has the `rejectSystemFeatures` attribute, then Nix will only build it on a machine that does not has the corresponding features set in its [`system-features` configuration](@docroot@/command-ref/conf-file.md#conf-system-features).

	ensures that the derivation can only be built on a machine which do not have the `pages-16k` feature.
	ensures that the derivation can only be built on a machine which does not have the `pages-16k` feature.

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RossComputerGuy commented Feb 11, 2025

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roberth commented Feb 19, 2025

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RossComputerGuy commented Mar 18, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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nixos-discourse commented Jun 4, 2025

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RossComputerGuy commented Mar 18, 2025 •

edited

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