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1fe66852ff
since `up` and `values` are both pointer-aligned the type field will
also be pointer-aligned, wasting 48 bits of space on most machines. we
can get away with removing the type field altogether by encoding some
information into the `with` expr that created the env to begin with,
reducing the GC load for the absolutely massive amount of single-entry
envs we create for lambdas. this reduces memory usage of system eval by
quite a bit (reducing heap size of our system eval from 8.4GB to 8.23GB)
and gives similar savings in eval time.
running `nix eval --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'`
before:
Time (mean ± σ): 5.576 s ± 0.003 s [User: 5.197 s, System: 0.378 s]
Range (min … max): 5.572 s … 5.581 s 10 runs
after:
Time (mean ± σ): 5.408 s ± 0.002 s [User: 5.019 s, System: 0.388 s]
Range (min … max): 5.405 s … 5.411 s 10 runs
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| .. | ||
| allowed-uris-can-now-match-whole-schemes.md | ||
| cgroup-stats.md | ||
| config | ||
| env-size-reduction.md | ||
| eval-system.md | ||
| hash-format-nix32.md | ||
| mounted-ssh-store.md | ||
| nix-config-show.md | ||
| nix-env-json-drv-path.md | ||
| nix-hash-convert.md | ||
| nix-profile-names.md | ||
| source-positions-in-errors.md | ||
| with-error-reporting.md | ||