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bench: fit the anchor tree to vscode's node_modules, 4 KiB files - #38
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F0..F7 said nothing: reading a result meant looking the id up in registry.py. Each id now names the tree's shape and file count (balanced-58k, wide-51k, deep-58k, balanced-58k-4kib, large-1mib-files, tiny-125, balanced-333k, flat-58k). That's what pytest ids, chart file names and Bencher benchmarks show: demo/balanced-58k/warm/remmy@4. A test keeps each id's file count in step with its tree. Trees, tools, sampling and the decision rule are unchanged.
The anchor (585 dirs x 100 empty files) was mktree's defaults, with no source for calling it typical. Measured eight real node_modules trees (express to bitwarden/clients): every one has ~7-10 files per dir, not 100, and ~80% of files are <= 4 KiB, so each frees one block; none are empty. The anchor is now vscode's shape made uniform: fanout 4, depth 6, 7 files per dir (5,461 dirs, 38,227 files; vscode c17dab9 has 5,538 and 39,966). Every small-file tree uses 4 KiB files. The trees that vary one thing of the anchor follow it: wide-38k keeps its dirs and files at one level, flat-38k its file count in one dir, deep-36k a similar count. The huge tree is the anchor one level deeper (152k files, monorepo sized) instead of 333k, which at 4 KiB would write 1.3 GB per run. balanced-58k-4kib is gone: the anchor is that now.
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Stacked on #36.
Summary
The anchor tree (585 dirs × 100 empty files) was just
mktree's defaults; nothing backed calling it a typicalnode_modules. I measured real ones (npm ci --ignore-scripts, macOS arm64, 2026-09-28):7de40fec17dab9852b61cbac4c66Every real tree has ~7–10 files per dir (the anchor had 100, so it underweighted directory work ~12×), ~2.7 subdirs per non-leaf dir, and median file size ~1 KiB. No real tree is empty files: APFS and ext4 give each small file one 4 KiB block to free.
The trees, all 4 KiB files except the 1 MiB one:
balanced-58kbalanced-38kwide-51kwide-38kdeep-58kdeep-36kbalanced-58k-4kiblarge-1mib-filestiny-125tiny-125balanced-333kbalanced-152kflat-58kflat-38kA uniform tree isn't a perfect fit: 75% of its dirs are leaves (vscode: 63%), and files sit deeper. Good enough for a synthetic benchmark.
Bencher: new names again, so new series. README: its charts and "58,500-file tree" come from the old trees and need a new full run.
Test plan
ruff check,ruff format --check, 36 bench unit tests (one fewer fixture)--bench=fullcollection lists the new idsmktreebuilds each new tree (except the unchanged 1 MiB one) with exactly the expected dir and file counts (≤ 4 s each)