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[Due for payment 2026-09-02] [No QA] Prevent sticky disks from growing unboundedly #98593
Description
Problem
A Blacksmith sticky disk is an ext4 block device, not a tarball, and the sticky disk action commits the mount in its post-job phase. Every job therefore snapshots whatever it wrote into node_modules before it ended — ESLint/Babel/rspack caches in node_modules/.cache, and Gradle/CMake output for native React Native libraries in node_modules/<lib>/android/build and .cxx. Because commit defaults to true, each run layered its generated files onto the previous snapshot and the next run started from that fatter disk.
The growth compounds worse than the file listing suggests: freed ext4 blocks are never returned to the storage layer, because fstrim on a sticky disk mount fails with the discard operation is not supported. A node_modules that is 3.8 GB after a clean npm ci reported 30 GB of live files and 103 GB of allocated blocks after about 3 weeks on the same key. At $0.50/GB/month, one key cost roughly $50/month.
Solution
Separate who produces the snapshot from who consumes it. setupNode gains a SEED_STICKY_DISKS input that selects the commit mode of the node_modules disks. A new seedStickyDisks.yml workflow passes SEED_STICKY_DISKS: 'true' to get commit: if-missing, installs dependencies and does nothing else, so its snapshot is a clean npm ci result by construction. It runs on every pull request and every push to main, and is a no-op once a key already has a snapshot.
Every other workflow keeps the default and mounts with commit: false. Jobs still read node_modules from the snapshot and may write caches, Gradle output and .cxx into their own clone, but the clone is discarded on unmount instead of committed, so disks stay at clean-install size permanently. The ~/.npm disk keeps committing with commit: on-change, since its key carries no hash and it must absorb new tarballs across lockfile bumps. Cache-hit detection is unchanged: the node_modules/.stickydisk-installed marker is written at the end of setupNode, so it lands in the seed snapshot and consumers skip npm ci when they see it.
Activity
[-][No QA] Prevent sticky disks from growing unboundedly[/-][+][Due for payment 2026-08-28] [No QA] Prevent sticky disks from growing unboundedly[/+]melvin-bot commentedon Aug 21, 2026
@mountiny @collectioneur
The solution for this issue has been 🚀 deployed to production 🚀 in version 9.4.57-3 and is now subject to a 7-day regression period 📆. Here is the list of pull requests that resolve this issue:
If no regressions arise, payment will be issued on 2026-08-28. 🎊
The following checklist (instructions) will need to be completed before the issue can be closed. Please copy/paste the Contributor+ Checklist from here into a new comment on this GH and complete it. If you have the K2 extension, you can simply click: [this button]. If no checklist is needed for this issue, you can click: [no checklist button]
[-][Due for payment 2026-08-28] [No QA] Prevent sticky disks from growing unboundedly[/-][+][No QA] Prevent sticky disks from growing unboundedly[/+]mountiny commentedon Aug 21, 2026
We still need to follow up
melvin-bot commentedon Aug 24, 2026
@collectioneur Uh oh! This issue is overdue by 2 days. Don't forget to update your issues!
[-][No QA] Prevent sticky disks from growing unboundedly[/-][+][Due for payment 2026-09-02] [No QA] Prevent sticky disks from growing unboundedly[/+]melvin-bot commentedon Aug 26, 2026
@mountiny @collectioneur
The solution for this issue has been 🚀 deployed to production 🚀 in version 9.4.61-4 and is now subject to a 7-day regression period 📆. Here is the list of pull requests that resolve this issue:
If no regressions arise, payment will be issued on 2026-09-02. 🎊
The following checklist (instructions) will need to be completed before the issue can be closed. Please copy/paste the Contributor+ Checklist from here into a new comment on this GH and complete it. If you have the K2 extension, you can simply click: [this button]. If no checklist is needed for this issue, you can click: [no checklist button]