nixos/qemu-vm: Use disposable EROFS for store when writableStore = false#181746
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roberth merged 4 commits intoNixOS:masterfrom Aug 14, 2022
Merged
nixos/qemu-vm: Use disposable EROFS for store when writableStore = false#181746roberth merged 4 commits intoNixOS:masterfrom
roberth merged 4 commits intoNixOS:masterfrom
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@ofborg test gitlab discourse simple installer.simple |
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viraptor
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This avoids putting a large disk image in the store (and possibly in a binary cache), while improving runtime performance. Assuming you're running an SSD, and/or with plenty of cache (?) it is feasible to preempt the virtualization overhead before VM start, in single-digit seconds. For some tests that perform many reads on the store, the improved performance of EROFS is sufficient that not only the image creation overhead is compensated for, but is actually faster. Stats for nixosTests.gitlab: Baseline without useNixStoreImage: >1000s Baseline with useNixStoreImage without writableStore = false ext4 image in store: 277 seconds + significant image build time and/or disk space Disposable erofs image: 249 seconds _including_ image build time Custom erofs overlay on 9p host store: 391 seconds; presumably because the overlay still performs too many 9p accesses, or perhaps some other overhead. This solution had no obvious performance advantage, while requiring extra options to work, so it was discarded.
knedlsepp
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Aug 14, 2022
| for more frequent garbage collection. | ||
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| If you really need this combination, you can set ${opt.writableStore} | ||
| explicitly to false, incur the cost and make this warning go away. |
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I'm confused about the message. Shouldn't it say "explicitly to true"? This paragraph essentially says "set it to false to incur the cost, otherwise we recommend to set it to false", no?
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This pull request has been mentioned on NixOS Discourse. There might be relevant details there: |
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This avoids putting a large disk image in the store (and possibly
in a binary cache), while improving runtime performance.
Assuming you're running an SSD, and/or with plenty of cache (?)
it is feasible to preempt the virtualization overhead before
VM start, in single-digit seconds.
For some tests that perform many reads on the store, the improved
performance of EROFS is sufficient that not only the image creation
overhead is compensated for, but is actually faster.
Stats for nixosTests.gitlab:
Baseline without useNixStoreImage: >1000s
Baseline with useNixStoreImage without writableStore = false
ext4 image in store: 277 seconds
+ significant image build time and/or disk space
Disposable erofs image: 249 seconds including image build time
Custom erofs overlay on 9p host store: 391 seconds; presumably
because the overlay still performs too many 9p accesses, or perhaps
some other overhead. This solution had no obvious performance
advantage, while requiring extra options to work, so it was
discarded.
Description of changes
Things done
sandbox = trueset innix.conf? (See Nix manual)nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage./result/bin/)nixos/doc/manual/md-to-db.shto update generated release notes