Building ISO takes excessive amounts of time+memory

[Slabity]

Issue description

When trying to build an ISO image, my system memory (~12GB) and swap space (~16GB) gets completely filled. The build seems to freeze on the following:

evaluating file '/nix/store/*/nixos/lib/systems/platform.nix'

Steps to reproduce

Using the following system configuration (file named iso.nix):

{config, pkgs, ...}:
{
  imports = [
    <nixpkgs/nixos/modules/installer/cd-dvd/installation-cd-graphical-gnome.nix>
    <nixpkgs/nixos/modules/installer/cd-dvd/channel.nix>
  ];

  nixpkgs.overlays = [
    (self: super: { inherit (super.pkgsi686Linux) grub2_efi; })
  ];
}

Then run the following:

nix-build '<nixpkgs/nixos>' -A config.system.build.isoImage -I nixos-config=iso.nix

Technical details

• system: "x86_64-linux"
• host os: Linux 5.0.2, NixOS, 19.09pre173080.1222e289b50 (Loris)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.2

Appears to affect 19.03 channel as well.

[tilpner]

This occurs here too. ulimit seems ineffective in preventing the freeze, but SysRq+F (may need SysRq+R too) is useful to invoke the OOM-killer manually.

I tested it against nixos-19.03, so it's not particular to nixos-unstable.

[matthewbauer]

Can you try out 18.09 to see if this has been introduced recently?

[tilpner]

• Instantiation is sufficient to cause this
• Instantiation of config.system.build.toplevel has the same effect as config.system.build.isoImage
• It also happens with 18.09
• The last line of -vv output differs:
  • nixos-19.03: evaluating file '/nix/store/4wngdg5ri4n6950smk3swgxgrzpshqhd-source/lib/systems/platforms.nix'
  • nixos-18.09: evaluating file '/nix/store/qv6wc1js0fqmjmvkn9qh8xxhx3f43wcm-source/pkgs/tools/filesystems/jfsutils/default.nix'

[Slabity]

So I just tried this on an EC2 m5a.24xlarge instance to see if it would actually complete.

It maxed out all 371GB of memory and only used a single core. After about ~30 minutes it finally crashed from a stack overflow.

I should also note that the issue does not occur if the overlay line is removed from the configuration.

[matthewbauer]

Ah ok! It's probably an issue in pkgsi686Linux.

[danbst]

This can be resolved with this simple patch:

diff --git a/pkgs/top-level/stage.nix b/pkgs/top-level/stage.nix
index 0ee5c25b010..0ef7cd4341e 100644
--- a/pkgs/top-level/stage.nix
+++ b/pkgs/top-level/stage.nix
@@ -151,6 +151,9 @@ let
     # All packages built for i686 Linux.
     # Used by wine, firefox with debugging version of Flash, ...
     pkgsi686Linux = if stdenv.hostPlatform.isLinux && stdenv.hostPlatform.isx86 then nixpkgsFun {
+      overlays = [ (self': super': {
+        pkgsi686Linux = super';
+      })] ++ overlays;
       ${if stdenv.hostPlatform == stdenv.buildPlatform
         then "localSystem" else "crossSystem"} = {
         parsed = stdenv.hostPlatform.parsed // {

but I'd like to hear also @oxij's opinion, as he was last to touch this code.

[danbst]

Hey @Slabity! The issue is fixed in nixpkgs master and 19.03, but if you need it on 18.09, there is workaround:

  nixpkgs.overlays = [
    (self: super: super.lib.optionalAttrs (super.system != "i686-linux")  
       { inherit (super.pkgsi686Linux) grub2_efi; })
  ];